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API

This part of the documentation covers all the interfaces of Flask. For parts where Flask depends on external libraries, we document the most important right here and provide links to the canonical documentation.

Application Object

class flask.Flask(import_name: str, static_url_path: Optional[str] = None, static_folder: Optional[Union[str, os.PathLike]] = 'static', static_host: Optional[str] = None, host_matching: bool = False, subdomain_matching: bool = False, template_folder: Optional[str] = 'templates', instance_path: Optional[str] = None, instance_relative_config: bool = False, root_path: Optional[str] = None)

The flask object implements a WSGI application and acts as the central object. It is passed the name of the module or package of the application. Once it is created it will act as a central registry for the view functions, the URL rules, template configuration and much more.

The name of the package is used to resolve resources from inside the package or the folder the module is contained in depending on if the package parameter resolves to an actual python package (a folder with an __init__.py file inside) or a standard module (just a .py file).

For more information about resource loading, see open_resource().

Usually you create a Flask instance in your main module or in the __init__.py file of your package like this:

from flask import Flask
app = Flask(__name__)

About the First Parameter

The idea of the first parameter is to give Flask an idea of what belongs to your application. This name is used to find resources on the filesystem, can be used by extensions to improve debugging information and a lot more.

So it’s important what you provide there. If you are using a single module, __name__ is always the correct value. If you however are using a package, it’s usually recommended to hardcode the name of your package there.

For example if your application is defined in yourapplication/app.py you should create it with one of the two versions below:

app = Flask('yourapplication')
app = Flask(__name__.split('.')[0])

Why is that? The application will work even with __name__, thanks to how resources are looked up. However it will make debugging more painful. Certain extensions can make assumptions based on the import name of your application. For example the Flask-SQLAlchemy extension will look for the code in your application that triggered an SQL query in debug mode. If the import name is not properly set up, that debugging information is lost. (For example it would only pick up SQL queries in yourapplication.app and not yourapplication.views.frontend)

New in version 0.7: The static_url_path, static_folder, and template_folder parameters were added.

New in version 0.8: The instance_path and instance_relative_config parameters were added.

New in version 0.11: The root_path parameter was added.

New in version 1.0: The host_matching and static_host parameters were added.

New in version 1.0: The subdomain_matching parameter was added. Subdomain matching needs to be enabled manually now. Setting SERVER_NAME does not implicitly enable it.

Parameters
  • import_name – the name of the application package

  • static_url_path – can be used to specify a different path for the static files on the web. Defaults to the name of the static_folder folder.

  • static_folder – The folder with static files that is served at static_url_path. Relative to the application root_path or an absolute path. Defaults to 'static'.

  • static_host – the host to use when adding the static route. Defaults to None. Required when using host_matching=True with a static_folder configured.

  • host_matching – set url_map.host_matching attribute. Defaults to False.

  • subdomain_matching – consider the subdomain relative to SERVER_NAME when matching routes. Defaults to False.

  • template_folder – the folder that contains the templates that should be used by the application. Defaults to 'templates' folder in the root path of the application.

  • instance_path – An alternative instance path for the application. By default the folder 'instance' next to the package or module is assumed to be the instance path.

  • instance_relative_config – if set to True relative filenames for loading the config are assumed to be relative to the instance path instead of the application root.

  • root_path – The path to the root of the application files. This should only be set manually when it can’t be detected automatically, such as for namespace packages.

add_template_filter(f: Callable[[...], Any], name: Optional[str] = None) None

Register a custom template filter. Works exactly like the template_filter() decorator.

Parameters

name – the optional name of the filter, otherwise the function name will be used.

add_template_global(f: Callable[[...], Any], name: Optional[str] = None) None

Register a custom template global function. Works exactly like the template_global() decorator.

New in version 0.10.

Parameters

name – the optional name of the global function, otherwise the function name will be used.

add_template_test(f: Callable[[...], bool], name: Optional[str] = None) None

Register a custom template test. Works exactly like the template_test() decorator.

New in version 0.10.

Parameters

name – the optional name of the test, otherwise the function name will be used.

add_url_rule(rule: str, endpoint: Optional[str] = None, view_func: Optional[Callable] = None, provide_automatic_options: Optional[bool] = None, **options: Any) None

Register a rule for routing incoming requests and building URLs. The route() decorator is a shortcut to call this with the view_func argument. These are equivalent:

@app.route("/")
def index():
    ...
def index():
    ...

app.add_url_rule("/", view_func=index)

See URL Route Registrations.

The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed. An error will be raised if a function has already been registered for the endpoint.

The methods parameter defaults to ["GET"]. HEAD is always added automatically, and OPTIONS is added automatically by default.

view_func does not necessarily need to be passed, but if the rule should participate in routing an endpoint name must be associated with a view function at some point with the endpoint() decorator.

app.add_url_rule("/", endpoint="index")

@app.endpoint("index")
def index():
    ...

If view_func has a required_methods attribute, those methods are added to the passed and automatic methods. If it has a provide_automatic_methods attribute, it is used as the default if the parameter is not passed.

Parameters
  • rule – The URL rule string.

  • endpoint – The endpoint name to associate with the rule and view function. Used when routing and building URLs. Defaults to view_func.__name__.

  • view_func – The view function to associate with the endpoint name.

  • provide_automatic_options – Add the OPTIONS method and respond to OPTIONS requests automatically.

  • options – Extra options passed to the Rule object.

after_request(f: Callable[[Response], Response]) Callable[[Response], Response]

Register a function to run after each request to this object.

The function is called with the response object, and must return a response object. This allows the functions to modify or replace the response before it is sent.

If a function raises an exception, any remaining after_request functions will not be called. Therefore, this should not be used for actions that must execute, such as to close resources. Use teardown_request() for that.

after_request_funcs: t.Dict[AppOrBlueprintKey, t.List[AfterRequestCallable]]

A data structure of functions to call at the end of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the after_request() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

app_context() flask.ctx.AppContext

Create an AppContext. Use as a with block to push the context, which will make current_app point at this application.

An application context is automatically pushed by RequestContext.push() when handling a request, and when running a CLI command. Use this to manually create a context outside of these situations.

with app.app_context():
    init_db()

See The Application Context.

New in version 0.9.

app_ctx_globals_class

alias of flask.ctx._AppCtxGlobals

async_to_sync(func: Callable[[...], Coroutine]) Callable[[...], Any]

Return a sync function that will run the coroutine function.

result = app.async_to_sync(func)(*args, **kwargs)

Override this method to change how the app converts async code to be synchronously callable.

New in version 2.0.

auto_find_instance_path() str

Tries to locate the instance path if it was not provided to the constructor of the application class. It will basically calculate the path to a folder named instance next to your main file or the package.

New in version 0.8.

before_first_request(f: Callable[[], None]) Callable[[], None]

Registers a function to be run before the first request to this instance of the application.

The function will be called without any arguments and its return value is ignored.

New in version 0.8.

before_first_request_funcs: t.List[BeforeFirstRequestCallable]

A list of functions that will be called at the beginning of the first request to this instance. To register a function, use the before_first_request() decorator.

New in version 0.8.

before_request(f: Callable[[], Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]]) Callable[[], Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]]

Register a function to run before each request.

For example, this can be used to open a database connection, or to load the logged in user from the session.

@app.before_request
def load_user():
    if "user_id" in session:
        g.user = db.session.get(session["user_id"])

The function will be called without any arguments. If it returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.

before_request_funcs: t.Dict[AppOrBlueprintKey, t.List[BeforeRequestCallable]]

A data structure of functions to call at the beginning of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the before_request() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

blueprints: t.Dict[str, 'Blueprint']

Maps registered blueprint names to blueprint objects. The dict retains the order the blueprints were registered in. Blueprints can be registered multiple times, this dict does not track how often they were attached.

New in version 0.7.

cli

The Click command group for registering CLI commands for this object. The commands are available from the flask command once the application has been discovered and blueprints have been registered.

config

The configuration dictionary as Config. This behaves exactly like a regular dictionary but supports additional methods to load a config from files.

config_class

alias of flask.config.Config

context_processor(f: Callable[[], Dict[str, Any]]) Callable[[], Dict[str, Any]]

Registers a template context processor function.

create_global_jinja_loader() flask.templating.DispatchingJinjaLoader

Creates the loader for the Jinja2 environment. Can be used to override just the loader and keeping the rest unchanged. It’s discouraged to override this function. Instead one should override the jinja_loader() function instead.

The global loader dispatches between the loaders of the application and the individual blueprints.

New in version 0.7.

create_jinja_environment() flask.templating.Environment

Create the Jinja environment based on jinja_options and the various Jinja-related methods of the app. Changing jinja_options after this will have no effect. Also adds Flask-related globals and filters to the environment.

Changed in version 0.11: Environment.auto_reload set in accordance with TEMPLATES_AUTO_RELOAD configuration option.

New in version 0.5.

create_url_adapter(request: Optional[flask.wrappers.Request]) Optional[werkzeug.routing.MapAdapter]

Creates a URL adapter for the given request. The URL adapter is created at a point where the request context is not yet set up so the request is passed explicitly.

New in version 0.6.

Changed in version 0.9: This can now also be called without a request object when the URL adapter is created for the application context.

Changed in version 1.0: SERVER_NAME no longer implicitly enables subdomain matching. Use subdomain_matching instead.

property debug: bool

Whether debug mode is enabled. When using flask run to start the development server, an interactive debugger will be shown for unhandled exceptions, and the server will be reloaded when code changes. This maps to the DEBUG config key. This is enabled when env is 'development' and is overridden by the FLASK_DEBUG environment variable. It may not behave as expected if set in code.

Do not enable debug mode when deploying in production.

Default: True if env is 'development', or False otherwise.

default_config = {'APPLICATION_ROOT': '/', 'DEBUG': None, 'ENV': None, 'EXPLAIN_TEMPLATE_LOADING': False, 'JSONIFY_MIMETYPE': 'application/json', 'JSONIFY_PRETTYPRINT_REGULAR': False, 'JSON_AS_ASCII': True, 'JSON_SORT_KEYS': True, 'MAX_CONTENT_LENGTH': None, 'MAX_COOKIE_SIZE': 4093, 'PERMANENT_SESSION_LIFETIME': datetime.timedelta(days=31), 'PREFERRED_URL_SCHEME': 'http', 'PRESERVE_CONTEXT_ON_EXCEPTION': None, 'PROPAGATE_EXCEPTIONS': None, 'SECRET_KEY': None, 'SEND_FILE_MAX_AGE_DEFAULT': None, 'SERVER_NAME': None, 'SESSION_COOKIE_DOMAIN': None, 'SESSION_COOKIE_HTTPONLY': True, 'SESSION_COOKIE_NAME': 'session', 'SESSION_COOKIE_PATH': None, 'SESSION_COOKIE_SAMESITE': None, 'SESSION_COOKIE_SECURE': False, 'SESSION_REFRESH_EACH_REQUEST': True, 'TEMPLATES_AUTO_RELOAD': None, 'TESTING': False, 'TRAP_BAD_REQUEST_ERRORS': None, 'TRAP_HTTP_EXCEPTIONS': False, 'USE_X_SENDFILE': False}

Default configuration parameters.

delete(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["DELETE"].

New in version 2.0.

dispatch_request() Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]

Does the request dispatching. Matches the URL and returns the return value of the view or error handler. This does not have to be a response object. In order to convert the return value to a proper response object, call make_response().

Changed in version 0.7: This no longer does the exception handling, this code was moved to the new full_dispatch_request().

do_teardown_appcontext(exc: typing.Optional[BaseException] = <object object>) None

Called right before the application context is popped.

When handling a request, the application context is popped after the request context. See do_teardown_request().

This calls all functions decorated with teardown_appcontext(). Then the appcontext_tearing_down signal is sent.

This is called by AppContext.pop().

New in version 0.9.

do_teardown_request(exc: typing.Optional[BaseException] = <object object>) None

Called after the request is dispatched and the response is returned, right before the request context is popped.

This calls all functions decorated with teardown_request(), and Blueprint.teardown_request() if a blueprint handled the request. Finally, the request_tearing_down signal is sent.

This is called by RequestContext.pop(), which may be delayed during testing to maintain access to resources.

Parameters

exc – An unhandled exception raised while dispatching the request. Detected from the current exception information if not passed. Passed to each teardown function.

Changed in version 0.9: Added the exc argument.

endpoint(endpoint: str) Callable

Decorate a view function to register it for the given endpoint. Used if a rule is added without a view_func with add_url_rule().

app.add_url_rule("/ex", endpoint="example")

@app.endpoint("example")
def example():
    ...
Parameters

endpoint – The endpoint name to associate with the view function.

ensure_sync(func: Callable) Callable

Ensure that the function is synchronous for WSGI workers. Plain def functions are returned as-is. async def functions are wrapped to run and wait for the response.

Override this method to change how the app runs async views.

New in version 2.0.

env

What environment the app is running in. Flask and extensions may enable behaviors based on the environment, such as enabling debug mode. This maps to the ENV config key. This is set by the FLASK_ENV environment variable and may not behave as expected if set in code.

Do not enable development when deploying in production.

Default: 'production'

error_handler_spec: t.Dict[AppOrBlueprintKey, t.Dict[t.Optional[int], t.Dict[t.Type[Exception], 'ErrorHandlerCallable']]]

A data structure of registered error handlers, in the format {scope: {code: {class: handler}}}`. The scope key is the name of a blueprint the handlers are active for, or None for all requests. The code key is the HTTP status code for HTTPException, or None for other exceptions. The innermost dictionary maps exception classes to handler functions.

To register an error handler, use the errorhandler() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

errorhandler(code_or_exception: Union[Type[Exception], int]) Callable[[ErrorHandlerCallable], ErrorHandlerCallable]

Register a function to handle errors by code or exception class.

A decorator that is used to register a function given an error code. Example:

@app.errorhandler(404)
def page_not_found(error):
    return 'This page does not exist', 404

You can also register handlers for arbitrary exceptions:

@app.errorhandler(DatabaseError)
def special_exception_handler(error):
    return 'Database connection failed', 500

New in version 0.7: Use register_error_handler() instead of modifying error_handler_spec directly, for application wide error handlers.

New in version 0.7: One can now additionally also register custom exception types that do not necessarily have to be a subclass of the HTTPException class.

Parameters

code_or_exception – the code as integer for the handler, or an arbitrary exception

extensions: dict

a place where extensions can store application specific state. For example this is where an extension could store database engines and similar things.

The key must match the name of the extension module. For example in case of a “Flask-Foo” extension in flask_foo, the key would be 'foo'.

New in version 0.7.

full_dispatch_request() flask.wrappers.Response

Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling.

New in version 0.7.

get(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["GET"].

New in version 2.0.

get_send_file_max_age(filename: Optional[str]) Optional[int]

Used by send_file() to determine the max_age cache value for a given file path if it wasn’t passed.

By default, this returns SEND_FILE_MAX_AGE_DEFAULT from the configuration of current_app. This defaults to None, which tells the browser to use conditional requests instead of a timed cache, which is usually preferable.

Changed in version 2.0: The default configuration is None instead of 12 hours.

New in version 0.9.

property got_first_request: bool

This attribute is set to True if the application started handling the first request.

New in version 0.8.

handle_exception(e: Exception) flask.wrappers.Response

Handle an exception that did not have an error handler associated with it, or that was raised from an error handler. This always causes a 500 InternalServerError.

Always sends the got_request_exception signal.

If propagate_exceptions is True, such as in debug mode, the error will be re-raised so that the debugger can display it. Otherwise, the original exception is logged, and an InternalServerError is returned.

If an error handler is registered for InternalServerError or 500, it will be used. For consistency, the handler will always receive the InternalServerError. The original unhandled exception is available as e.original_exception.

Changed in version 1.1.0: Always passes the InternalServerError instance to the handler, setting original_exception to the unhandled error.

Changed in version 1.1.0: after_request functions and other finalization is done even for the default 500 response when there is no handler.

New in version 0.3.

handle_http_exception(e: werkzeug.exceptions.HTTPException) Union[werkzeug.exceptions.HTTPException, Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]

Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response.

Changed in version 1.0.3: RoutingException, used internally for actions such as slash redirects during routing, is not passed to error handlers.

Changed in version 1.0: Exceptions are looked up by code and by MRO, so HTTPException subclasses can be handled with a catch-all handler for the base HTTPException.

New in version 0.3.

handle_url_build_error(error: Exception, endpoint: str, values: dict) str

Handle BuildError on url_for().

handle_user_exception(e: Exception) Union[werkzeug.exceptions.HTTPException, Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]

This method is called whenever an exception occurs that should be handled. A special case is HTTPException which is forwarded to the handle_http_exception() method. This function will either return a response value or reraise the exception with the same traceback.

Changed in version 1.0: Key errors raised from request data like form show the bad key in debug mode rather than a generic bad request message.

New in version 0.7.

property has_static_folder: bool

True if static_folder is set.

New in version 0.5.

import_name

The name of the package or module that this object belongs to. Do not change this once it is set by the constructor.

inject_url_defaults(endpoint: str, values: dict) None

Injects the URL defaults for the given endpoint directly into the values dictionary passed. This is used internally and automatically called on URL building.

New in version 0.7.

instance_path

Holds the path to the instance folder.

New in version 0.8.

iter_blueprints() ValuesView[Blueprint]

Iterates over all blueprints by the order they were registered.

New in version 0.11.

property jinja_env: flask.templating.Environment

The Jinja environment used to load templates.

The environment is created the first time this property is accessed. Changing jinja_options after that will have no effect.

jinja_environment

alias of flask.templating.Environment

property jinja_loader: Optional[jinja2.loaders.FileSystemLoader]

The Jinja loader for this object’s templates. By default this is a class jinja2.loaders.FileSystemLoader to template_folder if it is set.

New in version 0.5.

jinja_options: dict = {}

Options that are passed to the Jinja environment in create_jinja_environment(). Changing these options after the environment is created (accessing jinja_env) will have no effect.

Changed in version 1.1.0: This is a dict instead of an ImmutableDict to allow easier configuration.

json_decoder

alias of flask.json.JSONDecoder

json_encoder

alias of flask.json.JSONEncoder

log_exception(exc_info: Union[Tuple[type, BaseException, types.TracebackType], Tuple[None, None, None]]) None

Logs an exception. This is called by handle_exception() if debugging is disabled and right before the handler is called. The default implementation logs the exception as error on the logger.

New in version 0.8.

property logger: logging.Logger

A standard Python Logger for the app, with the same name as name.

In debug mode, the logger’s level will be set to DEBUG.

If there are no handlers configured, a default handler will be added. See Logging for more information.

Changed in version 1.1.0: The logger takes the same name as name rather than hard-coding "flask.app".

Changed in version 1.0.0: Behavior was simplified. The logger is always named "flask.app". The level is only set during configuration, it doesn’t check app.debug each time. Only one format is used, not different ones depending on app.debug. No handlers are removed, and a handler is only added if no handlers are already configured.

New in version 0.3.

make_config(instance_relative: bool = False) flask.config.Config

Used to create the config attribute by the Flask constructor. The instance_relative parameter is passed in from the constructor of Flask (there named instance_relative_config) and indicates if the config should be relative to the instance path or the root path of the application.

New in version 0.8.

make_default_options_response() flask.wrappers.Response

This method is called to create the default OPTIONS response. This can be changed through subclassing to change the default behavior of OPTIONS responses.

New in version 0.7.

make_response(rv: Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]) flask.wrappers.Response

Convert the return value from a view function to an instance of response_class.

Parameters

rv

the return value from the view function. The view function must return a response. Returning None, or the view ending without returning, is not allowed. The following types are allowed for view_rv:

str

A response object is created with the string encoded to UTF-8 as the body.

bytes

A response object is created with the bytes as the body.

dict

A dictionary that will be jsonify’d before being returned.

tuple

Either (body, status, headers), (body, status), or (body, headers), where body is any of the other types allowed here, status is a string or an integer, and headers is a dictionary or a list of (key, value) tuples. If body is a response_class instance, status overwrites the exiting value and headers are extended.

response_class

The object is returned unchanged.

other Response class

The object is coerced to response_class.

callable()

The function is called as a WSGI application. The result is used to create a response object.

Changed in version 0.9: Previously a tuple was interpreted as the arguments for the response object.

make_shell_context() dict

Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors.

New in version 0.11.

property name: str

The name of the application. This is usually the import name with the difference that it’s guessed from the run file if the import name is main. This name is used as a display name when Flask needs the name of the application. It can be set and overridden to change the value.

New in version 0.8.

open_instance_resource(resource: str, mode: str = 'rb') IO

Opens a resource from the application’s instance folder (instance_path). Otherwise works like open_resource(). Instance resources can also be opened for writing.

Parameters
  • resource – the name of the resource. To access resources within subfolders use forward slashes as separator.

  • mode – resource file opening mode, default is ‘rb’.

open_resource(resource: str, mode: str = 'rb') IO

Open a resource file relative to root_path for reading.

For example, if the file schema.sql is next to the file app.py where the Flask app is defined, it can be opened with:

with app.open_resource("schema.sql") as f:
    conn.executescript(f.read())
Parameters
  • resource – Path to the resource relative to root_path.

  • mode – Open the file in this mode. Only reading is supported, valid values are “r” (or “rt”) and “rb”.

patch(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["PATCH"].

New in version 2.0.

permanent_session_lifetime

A timedelta which is used to set the expiration date of a permanent session. The default is 31 days which makes a permanent session survive for roughly one month.

This attribute can also be configured from the config with the PERMANENT_SESSION_LIFETIME configuration key. Defaults to timedelta(days=31)

post(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["POST"].

New in version 2.0.

preprocess_request() Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]

Called before the request is dispatched. Calls url_value_preprocessors registered with the app and the current blueprint (if any). Then calls before_request_funcs registered with the app and the blueprint.

If any before_request() handler returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.

property preserve_context_on_exception: bool

Returns the value of the PRESERVE_CONTEXT_ON_EXCEPTION configuration value in case it’s set, otherwise a sensible default is returned.

New in version 0.7.

process_response(response: flask.wrappers.Response) flask.wrappers.Response

Can be overridden in order to modify the response object before it’s sent to the WSGI server. By default this will call all the after_request() decorated functions.

Changed in version 0.5: As of Flask 0.5 the functions registered for after request execution are called in reverse order of registration.

Parameters

response – a response_class object.

Returns

a new response object or the same, has to be an instance of response_class.

property propagate_exceptions: bool

Returns the value of the PROPAGATE_EXCEPTIONS configuration value in case it’s set, otherwise a sensible default is returned.

New in version 0.7.

put(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["PUT"].

New in version 2.0.

register_blueprint(blueprint: Blueprint, **options: Any) None

Register a Blueprint on the application. Keyword arguments passed to this method will override the defaults set on the blueprint.

Calls the blueprint’s register() method after recording the blueprint in the application’s blueprints.

Parameters
  • blueprint – The blueprint to register.

  • url_prefix – Blueprint routes will be prefixed with this.

  • subdomain – Blueprint routes will match on this subdomain.

  • url_defaults – Blueprint routes will use these default values for view arguments.

  • options – Additional keyword arguments are passed to BlueprintSetupState. They can be accessed in record() callbacks.

Changed in version 2.0.1: The name option can be used to change the (pre-dotted) name the blueprint is registered with. This allows the same blueprint to be registered multiple times with unique names for url_for.

New in version 0.7.

register_error_handler(code_or_exception: Union[Type[Exception], int], f: ErrorHandlerCallable) None

Alternative error attach function to the errorhandler() decorator that is more straightforward to use for non decorator usage.

New in version 0.7.

request_class

alias of flask.wrappers.Request

request_context(environ: dict) flask.ctx.RequestContext

Create a RequestContext representing a WSGI environment. Use a with block to push the context, which will make request point at this request.

See The Request Context.

Typically you should not call this from your own code. A request context is automatically pushed by the wsgi_app() when handling a request. Use test_request_context() to create an environment and context instead of this method.

Parameters

environ – a WSGI environment

response_class

alias of flask.wrappers.Response

root_path

Absolute path to the package on the filesystem. Used to look up resources contained in the package.

route(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Decorate a view function to register it with the given URL rule and options. Calls add_url_rule(), which has more details about the implementation.

@app.route("/")
def index():
    return "Hello, World!"

See URL Route Registrations.

The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed.

The methods parameter defaults to ["GET"]. HEAD and OPTIONS are added automatically.

Parameters
  • rule – The URL rule string.

  • options – Extra options passed to the Rule object.

run(host: Optional[str] = None, port: Optional[int] = None, debug: Optional[bool] = None, load_dotenv: bool = True, **options: Any) None

Runs the application on a local development server.

Do not use run() in a production setting. It is not intended to meet security and performance requirements for a production server. Instead, see Deployment Options for WSGI server recommendations.

If the debug flag is set the server will automatically reload for code changes and show a debugger in case an exception happened.

If you want to run the application in debug mode, but disable the code execution on the interactive debugger, you can pass use_evalex=False as parameter. This will keep the debugger’s traceback screen active, but disable code execution.

It is not recommended to use this function for development with automatic reloading as this is badly supported. Instead you should be using the flask command line script’s run support.

Keep in Mind

Flask will suppress any server error with a generic error page unless it is in debug mode. As such to enable just the interactive debugger without the code reloading, you have to invoke run() with debug=True and use_reloader=False. Setting use_debugger to True without being in debug mode won’t catch any exceptions because there won’t be any to catch.

Parameters
  • host – the hostname to listen on. Set this to '0.0.0.0' to have the server available externally as well. Defaults to '127.0.0.1' or the host in the SERVER_NAME config variable if present.

  • port – the port of the webserver. Defaults to 5000 or the port defined in the SERVER_NAME config variable if present.

  • debug – if given, enable or disable debug mode. See debug.

  • load_dotenv – Load the nearest .env and .flaskenv files to set environment variables. Will also change the working directory to the directory containing the first file found.

  • options – the options to be forwarded to the underlying Werkzeug server. See werkzeug.serving.run_simple() for more information.

Changed in version 1.0: If installed, python-dotenv will be used to load environment variables from .env and .flaskenv files.

If set, the FLASK_ENV and FLASK_DEBUG environment variables will override env and debug.

Threaded mode is enabled by default.

Changed in version 0.10: The default port is now picked from the SERVER_NAME variable.

secret_key

If a secret key is set, cryptographic components can use this to sign cookies and other things. Set this to a complex random value when you want to use the secure cookie for instance.

This attribute can also be configured from the config with the SECRET_KEY configuration key. Defaults to None.

select_jinja_autoescape(filename: str) bool

Returns True if autoescaping should be active for the given template name. If no template name is given, returns True.

New in version 0.5.

send_file_max_age_default

A timedelta or number of seconds which is used as the default max_age for send_file(). The default is None, which tells the browser to use conditional requests instead of a timed cache.

Configured with the SEND_FILE_MAX_AGE_DEFAULT configuration key.

Changed in version 2.0: Defaults to None instead of 12 hours.

send_static_file(filename: str) Response

The view function used to serve files from static_folder. A route is automatically registered for this view at static_url_path if static_folder is set.

New in version 0.5.

The secure cookie uses this for the name of the session cookie.

This attribute can also be configured from the config with the SESSION_COOKIE_NAME configuration key. Defaults to 'session'

session_interface: flask.sessions.SessionInterface = <flask.sessions.SecureCookieSessionInterface object>

the session interface to use. By default an instance of SecureCookieSessionInterface is used here.

New in version 0.8.

shell_context_processor(f: Callable) Callable

Registers a shell context processor function.

New in version 0.11.

shell_context_processors: t.List[t.Callable[[], t.Dict[str, t.Any]]]

A list of shell context processor functions that should be run when a shell context is created.

New in version 0.11.

should_ignore_error(error: Optional[BaseException]) bool

This is called to figure out if an error should be ignored or not as far as the teardown system is concerned. If this function returns True then the teardown handlers will not be passed the error.

New in version 0.10.

property static_folder: Optional[str]

The absolute path to the configured static folder. None if no static folder is set.

property static_url_path: Optional[str]

The URL prefix that the static route will be accessible from.

If it was not configured during init, it is derived from static_folder.

teardown_appcontext(f: Callable[[Optional[BaseException]], None]) Callable[[Optional[BaseException]], None]

Registers a function to be called when the application context ends. These functions are typically also called when the request context is popped.

Example:

ctx = app.app_context()
ctx.push()
...
ctx.pop()

When ctx.pop() is executed in the above example, the teardown functions are called just before the app context moves from the stack of active contexts. This becomes relevant if you are using such constructs in tests.

Since a request context typically also manages an application context it would also be called when you pop a request context.

When a teardown function was called because of an unhandled exception it will be passed an error object. If an errorhandler() is registered, it will handle the exception and the teardown will not receive it.

The return values of teardown functions are ignored.

New in version 0.9.

teardown_appcontext_funcs: t.List[TeardownCallable]

A list of functions that are called when the application context is destroyed. Since the application context is also torn down if the request ends this is the place to store code that disconnects from databases.

New in version 0.9.

teardown_request(f: Callable[[Optional[BaseException]], None]) Callable[[Optional[BaseException]], None]

Register a function to be run at the end of each request, regardless of whether there was an exception or not. These functions are executed when the request context is popped, even if not an actual request was performed.

Example:

ctx = app.test_request_context()
ctx.push()
...
ctx.pop()

When ctx.pop() is executed in the above example, the teardown functions are called just before the request context moves from the stack of active contexts. This becomes relevant if you are using such constructs in tests.

Teardown functions must avoid raising exceptions. If they execute code that might fail they will have to surround the execution of that code with try/except statements and log any errors.

When a teardown function was called because of an exception it will be passed an error object.

The return values of teardown functions are ignored.

Debug Note

In debug mode Flask will not tear down a request on an exception immediately. Instead it will keep it alive so that the interactive debugger can still access it. This behavior can be controlled by the PRESERVE_CONTEXT_ON_EXCEPTION configuration variable.

teardown_request_funcs: t.Dict[AppOrBlueprintKey, t.List[TeardownCallable]]

A data structure of functions to call at the end of each request even if an exception is raised, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the teardown_request() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

template_context_processors: t.Dict[AppOrBlueprintKey, t.List[TemplateContextProcessorCallable]]

A data structure of functions to call to pass extra context values when rendering templates, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the context_processor() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

template_filter(name: Optional[str] = None) Callable[[Callable[[...], Any]], Callable[[...], Any]]

A decorator that is used to register custom template filter. You can specify a name for the filter, otherwise the function name will be used. Example:

@app.template_filter()
def reverse(s):
    return s[::-1]
Parameters

name – the optional name of the filter, otherwise the function name will be used.

template_folder

The path to the templates folder, relative to root_path, to add to the template loader. None if templates should not be added.

template_global(name: Optional[str] = None) Callable[[Callable[[...], Any]], Callable[[...], Any]]

A decorator that is used to register a custom template global function. You can specify a name for the global function, otherwise the function name will be used. Example:

@app.template_global()
def double(n):
    return 2 * n

New in version 0.10.

Parameters

name – the optional name of the global function, otherwise the function name will be used.

template_test(name: Optional[str] = None) Callable[[Callable[[...], bool]], Callable[[...], bool]]

A decorator that is used to register custom template test. You can specify a name for the test, otherwise the function name will be used. Example:

@app.template_test()
def is_prime(n):
    if n == 2:
        return True
    for i in range(2, int(math.ceil(math.sqrt(n))) + 1):
        if n % i == 0:
            return False
    return True

New in version 0.10.

Parameters

name – the optional name of the test, otherwise the function name will be used.

property templates_auto_reload: bool

Reload templates when they are changed. Used by create_jinja_environment().

This attribute can be configured with TEMPLATES_AUTO_RELOAD. If not set, it will be enabled in debug mode.

New in version 1.0: This property was added but the underlying config and behavior already existed.

test_cli_runner(**kwargs: Any) FlaskCliRunner

Create a CLI runner for testing CLI commands. See Testing CLI Commands.

Returns an instance of test_cli_runner_class, by default FlaskCliRunner. The Flask app object is passed as the first argument.

New in version 1.0.

test_cli_runner_class: Optional[Type[FlaskCliRunner]] = None

The CliRunner subclass, by default FlaskCliRunner that is used by test_cli_runner(). Its __init__ method should take a Flask app object as the first argument.

New in version 1.0.

test_client(use_cookies: bool = True, **kwargs: Any) FlaskClient

Creates a test client for this application. For information about unit testing head over to Testing Flask Applications.

Note that if you are testing for assertions or exceptions in your application code, you must set app.testing = True in order for the exceptions to propagate to the test client. Otherwise, the exception will be handled by the application (not visible to the test client) and the only indication of an AssertionError or other exception will be a 500 status code response to the test client. See the testing attribute. For example:

app.testing = True
client = app.test_client()

The test client can be used in a with block to defer the closing down of the context until the end of the with block. This is useful if you want to access the context locals for testing:

with app.test_client() as c:
    rv = c.get('/?vodka=42')
    assert request.args['vodka'] == '42'

Additionally, you may pass optional keyword arguments that will then be passed to the application’s test_client_class constructor. For example:

from flask.testing import FlaskClient

class CustomClient(FlaskClient):
    def __init__(self, *args, **kwargs):
        self._authentication = kwargs.pop("authentication")
        super(CustomClient,self).__init__( *args, **kwargs)

app.test_client_class = CustomClient
client = app.test_client(authentication='Basic ....')

See FlaskClient for more information.

Changed in version 0.4: added support for with block usage for the client.

New in version 0.7: The use_cookies parameter was added as well as the ability to override the client to be used by setting the test_client_class attribute.

Changed in version 0.11: Added **kwargs to support passing additional keyword arguments to the constructor of test_client_class.

test_client_class: Optional[Type[FlaskClient]] = None

The test_client() method creates an instance of this test client class. Defaults to FlaskClient.

New in version 0.7.

test_request_context(*args: Any, **kwargs: Any) flask.ctx.RequestContext

Create a RequestContext for a WSGI environment created from the given values. This is mostly useful during testing, where you may want to run a function that uses request data without dispatching a full request.

See The Request Context.

Use a with block to push the context, which will make request point at the request for the created environment.

with test_request_context(...):
    generate_report()

When using the shell, it may be easier to push and pop the context manually to avoid indentation.

ctx = app.test_request_context(...)
ctx.push()
...
ctx.pop()

Takes the same arguments as Werkzeug’s EnvironBuilder, with some defaults from the application. See the linked Werkzeug docs for most of the available arguments. Flask-specific behavior is listed here.

Parameters
  • path – URL path being requested.

  • base_url – Base URL where the app is being served, which path is relative to. If not given, built from PREFERRED_URL_SCHEME, subdomain, SERVER_NAME, and APPLICATION_ROOT.

  • subdomain – Subdomain name to append to SERVER_NAME.

  • url_scheme – Scheme to use instead of PREFERRED_URL_SCHEME.

  • data – The request body, either as a string or a dict of form keys and values.

  • json – If given, this is serialized as JSON and passed as data. Also defaults content_type to application/json.

  • args – other positional arguments passed to EnvironBuilder.

  • kwargs – other keyword arguments passed to EnvironBuilder.

testing

The testing flag. Set this to True to enable the test mode of Flask extensions (and in the future probably also Flask itself). For example this might activate test helpers that have an additional runtime cost which should not be enabled by default.

If this is enabled and PROPAGATE_EXCEPTIONS is not changed from the default it’s implicitly enabled.

This attribute can also be configured from the config with the TESTING configuration key. Defaults to False.

trap_http_exception(e: Exception) bool

Checks if an HTTP exception should be trapped or not. By default this will return False for all exceptions except for a bad request key error if TRAP_BAD_REQUEST_ERRORS is set to True. It also returns True if TRAP_HTTP_EXCEPTIONS is set to True.

This is called for all HTTP exceptions raised by a view function. If it returns True for any exception the error handler for this exception is not called and it shows up as regular exception in the traceback. This is helpful for debugging implicitly raised HTTP exceptions.

Changed in version 1.0: Bad request errors are not trapped by default in debug mode.

New in version 0.8.

update_template_context(context: dict) None

Update the template context with some commonly used variables. This injects request, session, config and g into the template context as well as everything template context processors want to inject. Note that the as of Flask 0.6, the original values in the context will not be overridden if a context processor decides to return a value with the same key.

Parameters

context – the context as a dictionary that is updated in place to add extra variables.

url_build_error_handlers: t.List[t.Callable[[Exception, str, dict], str]]

A list of functions that are called when url_for() raises a BuildError. Each function registered here is called with error, endpoint and values. If a function returns None or raises a BuildError the next function is tried.

New in version 0.9.

url_default_functions: t.Dict[AppOrBlueprintKey, t.List[URLDefaultCallable]]

A data structure of functions to call to modify the keyword arguments when generating URLs, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the url_defaults() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

url_defaults(f: Callable[[str, dict], None]) Callable[[str, dict], None]

Callback function for URL defaults for all view functions of the application. It’s called with the endpoint and values and should update the values passed in place.

url_map

The Map for this instance. You can use this to change the routing converters after the class was created but before any routes are connected. Example:

from werkzeug.routing import BaseConverter

class ListConverter(BaseConverter):
    def to_python(self, value):
        return value.split(',')
    def to_url(self, values):
        return ','.join(super(ListConverter, self).to_url(value)
                        for value in values)

app = Flask(__name__)
app.url_map.converters['list'] = ListConverter
url_map_class

alias of werkzeug.routing.Map

url_rule_class

alias of werkzeug.routing.Rule

url_value_preprocessor(f: Callable[[Optional[str], Optional[dict]], None]) Callable[[Optional[str], Optional[dict]], None]

Register a URL value preprocessor function for all view functions in the application. These functions will be called before the before_request() functions.

The function can modify the values captured from the matched url before they are passed to the view. For example, this can be used to pop a common language code value and place it in g rather than pass it to every view.

The function is passed the endpoint name and values dict. The return value is ignored.

url_value_preprocessors: t.Dict[AppOrBlueprintKey, t.List[URLValuePreprocessorCallable]]

A data structure of functions to call to modify the keyword arguments passed to the view function, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the url_value_preprocessor() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

use_x_sendfile

Enable this if you want to use the X-Sendfile feature. Keep in mind that the server has to support this. This only affects files sent with the send_file() method.

New in version 0.2.

This attribute can also be configured from the config with the USE_X_SENDFILE configuration key. Defaults to False.

view_functions: t.Dict[str, t.Callable]

A dictionary mapping endpoint names to view functions.

To register a view function, use the route() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

wsgi_app(environ: dict, start_response: Callable) Any

The actual WSGI application. This is not implemented in __call__() so that middlewares can be applied without losing a reference to the app object. Instead of doing this:

app = MyMiddleware(app)

It’s a better idea to do this instead:

app.wsgi_app = MyMiddleware(app.wsgi_app)

Then you still have the original application object around and can continue to call methods on it.

Changed in version 0.7: Teardown events for the request and app contexts are called even if an unhandled error occurs. Other events may not be called depending on when an error occurs during dispatch. See Callbacks and Errors.

Parameters
  • environ – A WSGI environment.

  • start_response – A callable accepting a status code, a list of headers, and an optional exception context to start the response.

Blueprint Objects

class flask.Blueprint(name: str, import_name: str, static_folder: typing.Optional[typing.Union[str, os.PathLike]] = None, static_url_path: typing.Optional[str] = None, template_folder: typing.Optional[str] = None, url_prefix: typing.Optional[str] = None, subdomain: typing.Optional[str] = None, url_defaults: typing.Optional[dict] = None, root_path: typing.Optional[str] = None, cli_group: typing.Optional[str] = <object object>)

Represents a blueprint, a collection of routes and other app-related functions that can be registered on a real application later.

A blueprint is an object that allows defining application functions without requiring an application object ahead of time. It uses the same decorators as Flask, but defers the need for an application by recording them for later registration.

Decorating a function with a blueprint creates a deferred function that is called with BlueprintSetupState when the blueprint is registered on an application.

See Modular Applications with Blueprints for more information.

Parameters
  • name – The name of the blueprint. Will be prepended to each endpoint name.

  • import_name – The name of the blueprint package, usually __name__. This helps locate the root_path for the blueprint.

  • static_folder – A folder with static files that should be served by the blueprint’s static route. The path is relative to the blueprint’s root path. Blueprint static files are disabled by default.

  • static_url_path – The url to serve static files from. Defaults to static_folder. If the blueprint does not have a url_prefix, the app’s static route will take precedence, and the blueprint’s static files won’t be accessible.

  • template_folder – A folder with templates that should be added to the app’s template search path. The path is relative to the blueprint’s root path. Blueprint templates are disabled by default. Blueprint templates have a lower precedence than those in the app’s templates folder.

  • url_prefix – A path to prepend to all of the blueprint’s URLs, to make them distinct from the rest of the app’s routes.

  • subdomain – A subdomain that blueprint routes will match on by default.

  • url_defaults – A dict of default values that blueprint routes will receive by default.

  • root_path – By default, the blueprint will automatically set this based on import_name. In certain situations this automatic detection can fail, so the path can be specified manually instead.

Changed in version 1.1.0: Blueprints have a cli group to register nested CLI commands. The cli_group parameter controls the name of the group under the flask command.

New in version 0.7.

add_app_template_filter(f: Callable[[...], Any], name: Optional[str] = None) None

Register a custom template filter, available application wide. Like Flask.add_template_filter() but for a blueprint. Works exactly like the app_template_filter() decorator.

Parameters

name – the optional name of the filter, otherwise the function name will be used.

add_app_template_global(f: Callable[[...], Any], name: Optional[str] = None) None

Register a custom template global, available application wide. Like Flask.add_template_global() but for a blueprint. Works exactly like the app_template_global() decorator.

New in version 0.10.

Parameters

name – the optional name of the global, otherwise the function name will be used.

add_app_template_test(f: Callable[[...], bool], name: Optional[str] = None) None

Register a custom template test, available application wide. Like Flask.add_template_test() but for a blueprint. Works exactly like the app_template_test() decorator.

New in version 0.10.

Parameters

name – the optional name of the test, otherwise the function name will be used.

add_url_rule(rule: str, endpoint: Optional[str] = None, view_func: Optional[Callable] = None, provide_automatic_options: Optional[bool] = None, **options: Any) None

Like Flask.add_url_rule() but for a blueprint. The endpoint for the url_for() function is prefixed with the name of the blueprint.

after_app_request(f: Callable[[Response], Response]) Callable[[Response], Response]

Like Flask.after_request() but for a blueprint. Such a function is executed after each request, even if outside of the blueprint.

after_request(f: Callable[[Response], Response]) Callable[[Response], Response]

Register a function to run after each request to this object.

The function is called with the response object, and must return a response object. This allows the functions to modify or replace the response before it is sent.

If a function raises an exception, any remaining after_request functions will not be called. Therefore, this should not be used for actions that must execute, such as to close resources. Use teardown_request() for that.

after_request_funcs: t.Dict[AppOrBlueprintKey, t.List[AfterRequestCallable]]

A data structure of functions to call at the end of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the after_request() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

app_context_processor(f: Callable[[], Dict[str, Any]]) Callable[[], Dict[str, Any]]

Like Flask.context_processor() but for a blueprint. Such a function is executed each request, even if outside of the blueprint.

app_errorhandler(code: Union[Type[Exception], int]) Callable

Like Flask.errorhandler() but for a blueprint. This handler is used for all requests, even if outside of the blueprint.

app_template_filter(name: Optional[str] = None) Callable[[Callable[[...], Any]], Callable[[...], Any]]

Register a custom template filter, available application wide. Like Flask.template_filter() but for a blueprint.

Parameters

name – the optional name of the filter, otherwise the function name will be used.

app_template_global(name: Optional[str] = None) Callable[[Callable[[...], Any]], Callable[[...], Any]]

Register a custom template global, available application wide. Like Flask.template_global() but for a blueprint.

New in version 0.10.

Parameters

name – the optional name of the global, otherwise the function name will be used.

app_template_test(name: Optional[str] = None) Callable[[Callable[[...], bool]], Callable[[...], bool]]

Register a custom template test, available application wide. Like Flask.template_test() but for a blueprint.

New in version 0.10.

Parameters

name – the optional name of the test, otherwise the function name will be used.

app_url_defaults(f: Callable[[str, dict], None]) Callable[[str, dict], None]

Same as url_defaults() but application wide.

app_url_value_preprocessor(f: Callable[[Optional[str], Optional[dict]], None]) Callable[[Optional[str], Optional[dict]], None]

Same as url_value_preprocessor() but application wide.

before_app_first_request(f: Callable[[], None]) Callable[[], None]

Like Flask.before_first_request(). Such a function is executed before the first request to the application.

before_app_request(f: Callable[[], Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]]) Callable[[], Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]]

Like Flask.before_request(). Such a function is executed before each request, even if outside of a blueprint.

before_request(f: Callable[[], Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]]) Callable[[], Optional[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int], Tuple[Union[Response, str, bytes, Dict[str, Any], Iterator[str], Iterator[bytes]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]]

Register a function to run before each request.

For example, this can be used to open a database connection, or to load the logged in user from the session.

@app.before_request
def load_user():
    if "user_id" in session:
        g.user = db.session.get(session["user_id"])

The function will be called without any arguments. If it returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.

before_request_funcs: t.Dict[AppOrBlueprintKey, t.List[BeforeRequestCallable]]

A data structure of functions to call at the beginning of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the before_request() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

cli

The Click command group for registering CLI commands for this object. The commands are available from the flask command once the application has been discovered and blueprints have been registered.

context_processor(f: Callable[[], Dict[str, Any]]) Callable[[], Dict[str, Any]]

Registers a template context processor function.

delete(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["DELETE"].

New in version 2.0.

endpoint(endpoint: str) Callable

Decorate a view function to register it for the given endpoint. Used if a rule is added without a view_func with add_url_rule().

app.add_url_rule("/ex", endpoint="example")

@app.endpoint("example")
def example():
    ...
Parameters

endpoint – The endpoint name to associate with the view function.

error_handler_spec: t.Dict[AppOrBlueprintKey, t.Dict[t.Optional[int], t.Dict[t.Type[Exception], 'ErrorHandlerCallable']]]

A data structure of registered error handlers, in the format {scope: {code: {class: handler}}}`. The scope key is the name of a blueprint the handlers are active for, or None for all requests. The code key is the HTTP status code for HTTPException, or None for other exceptions. The innermost dictionary maps exception classes to handler functions.

To register an error handler, use the errorhandler() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

errorhandler(code_or_exception: Union[Type[Exception], int]) Callable[[ErrorHandlerCallable], ErrorHandlerCallable]

Register a function to handle errors by code or exception class.

A decorator that is used to register a function given an error code. Example:

@app.errorhandler(404)
def page_not_found(error):
    return 'This page does not exist', 404

You can also register handlers for arbitrary exceptions:

@app.errorhandler(DatabaseError)
def special_exception_handler(error):
    return 'Database connection failed', 500

New in version 0.7: Use register_error_handler() instead of modifying error_handler_spec directly, for application wide error handlers.

New in version 0.7: One can now additionally also register custom exception types that do not necessarily have to be a subclass of the HTTPException class.

Parameters

code_or_exception – the code as integer for the handler, or an arbitrary exception

get(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["GET"].

New in version 2.0.

get_send_file_max_age(filename: Optional[str]) Optional[int]

Used by send_file() to determine the max_age cache value for a given file path if it wasn’t passed.

By default, this returns SEND_FILE_MAX_AGE_DEFAULT from the configuration of current_app. This defaults to None, which tells the browser to use conditional requests instead of a timed cache, which is usually preferable.

Changed in version 2.0: The default configuration is None instead of 12 hours.

New in version 0.9.

property has_static_folder: bool

True if static_folder is set.

New in version 0.5.

import_name

The name of the package or module that this object belongs to. Do not change this once it is set by the constructor.

property jinja_loader: Optional[jinja2.loaders.FileSystemLoader]

The Jinja loader for this object’s templates. By default this is a class jinja2.loaders.FileSystemLoader to template_folder if it is set.

New in version 0.5.

json_decoder: t.Optional[t.Type[JSONDecoder]] = None

Blueprint local JSON decoder class to use. Set to None to use the app’s json_decoder.

json_encoder: t.Optional[t.Type[JSONEncoder]] = None

Blueprint local JSON encoder class to use. Set to None to use the app’s json_encoder.

make_setup_state(app: Flask, options: dict, first_registration: bool = False) flask.blueprints.BlueprintSetupState

Creates an instance of BlueprintSetupState() object that is later passed to the register callback functions. Subclasses can override this to return a subclass of the setup state.

open_resource(resource: str, mode: str = 'rb') IO

Open a resource file relative to root_path for reading.

For example, if the file schema.sql is next to the file app.py where the Flask app is defined, it can be opened with:

with app.open_resource("schema.sql") as f:
    conn.executescript(f.read())
Parameters
  • resource – Path to the resource relative to root_path.

  • mode – Open the file in this mode. Only reading is supported, valid values are “r” (or “rt”) and “rb”.

patch(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["PATCH"].

New in version 2.0.

post(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["POST"].

New in version 2.0.

put(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Shortcut for route() with methods=["PUT"].

New in version 2.0.

record(func: Callable) None

Registers a function that is called when the blueprint is registered on the application. This function is called with the state as argument as returned by the make_setup_state() method.

record_once(func: Callable) None

Works like record() but wraps the function in another function that will ensure the function is only called once. If the blueprint is registered a second time on the application, the function passed is not called.

register(app: Flask, options: dict) None

Called by Flask.register_blueprint() to register all views and callbacks registered on the blueprint with the application. Creates a BlueprintSetupState and calls each record() callback with it.

Parameters
  • app – The application this blueprint is being registered with.

  • options – Keyword arguments forwarded from register_blueprint().

Changed in version 2.0.1: Nested blueprints are registered with their dotted name. This allows different blueprints with the same name to be nested at different locations.

Changed in version 2.0.1: The name option can be used to change the (pre-dotted) name the blueprint is registered with. This allows the same blueprint to be registered multiple times with unique names for url_for.

Changed in version 2.0.1: Registering the same blueprint with the same name multiple times is deprecated and will become an error in Flask 2.1.

register_blueprint(blueprint: flask.blueprints.Blueprint, **options: Any) None

Register a Blueprint on this blueprint. Keyword arguments passed to this method will override the defaults set on the blueprint.

Changed in version 2.0.1: The name option can be used to change the (pre-dotted) name the blueprint is registered with. This allows the same blueprint to be registered multiple times with unique names for url_for.

New in version 2.0.

register_error_handler(code_or_exception: Union[Type[Exception], int], f: ErrorHandlerCallable) None

Alternative error attach function to the errorhandler() decorator that is more straightforward to use for non decorator usage.

New in version 0.7.

root_path

Absolute path to the package on the filesystem. Used to look up resources contained in the package.

route(rule: str, **options: Any) Callable[[flask.scaffold.F], flask.scaffold.F]

Decorate a view function to register it with the given URL rule and options. Calls add_url_rule(), which has more details about the implementation.

@app.route("/")
def index():
    return "Hello, World!"

See URL Route Registrations.

The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed.

The methods parameter defaults to ["GET"]. HEAD and OPTIONS are added automatically.

Parameters
  • rule – The URL rule string.

  • options – Extra options passed to the Rule object.

send_static_file(filename: str) Response

The view function used to serve files from static_folder. A route is automatically registered for this view at static_url_path if static_folder is set.

New in version 0.5.

property static_folder: Optional[str]

The absolute path to the configured static folder. None if no static folder is set.

property static_url_path: Optional[str]

The URL prefix that the static route will be accessible from.

If it was not configured during init, it is derived from static_folder.

teardown_app_request(f: Callable[[Optional[BaseException]], None]) Callable[[Optional[BaseException]], None]

Like Flask.teardown_request() but for a blueprint. Such a function is executed when tearing down each request, even if outside of the blueprint.

teardown_request(f: Callable[[Optional[BaseException]], None]) Callable[[Optional[BaseException]], None]

Register a function to be run at the end of each request, regardless of whether there was an exception or not. These functions are executed when the request context is popped, even if not an actual request was performed.

Example:

ctx = app.test_request_context()
ctx.push()
...
ctx.pop()

When ctx.pop() is executed in the above example, the teardown functions are called just before the request context moves from the stack of active contexts. This becomes relevant if you are using such constructs in tests.

Teardown functions must avoid raising exceptions. If they execute code that might fail they will have to surround the execution of that code with try/except statements and log any errors.

When a teardown function was called because of an exception it will be passed an error object.

The return values of teardown functions are ignored.

Debug Note

In debug mode Flask will not tear down a request on an exception immediately. Instead it will keep it alive so that the interactive debugger can still access it. This behavior can be controlled by the PRESERVE_CONTEXT_ON_EXCEPTION configuration variable.

teardown_request_funcs: t.Dict[AppOrBlueprintKey, t.List[TeardownCallable]]

A data structure of functions to call at the end of each request even if an exception is raised, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the teardown_request() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

template_context_processors: t.Dict[AppOrBlueprintKey, t.List[TemplateContextProcessorCallable]]

A data structure of functions to call to pass extra context values when rendering templates, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the context_processor() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

template_folder

The path to the templates folder, relative to root_path, to add to the template loader. None if templates should not be added.

url_default_functions: t.Dict[AppOrBlueprintKey, t.List[URLDefaultCallable]]

A data structure of functions to call to modify the keyword arguments when generating URLs, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the url_defaults() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

url_defaults(f: Callable[[str, dict], None]) Callable[[str, dict], None]

Callback function for URL defaults for all view functions of the application. It’s called with the endpoint and values and should update the values passed in place.

url_value_preprocessor(f: Callable[[Optional[str], Optional[dict]], None]) Callable[[Optional[str], Optional[dict]], None]

Register a URL value preprocessor function for all view functions in the application. These functions will be called before the before_request() functions.

The function can modify the values captured from the matched url before they are passed to the view. For example, this can be used to pop a common language code value and place it in g rather than pass it to every view.

The function is passed the endpoint name and values dict. The return value is ignored.

url_value_preprocessors: t.Dict[AppOrBlueprintKey, t.List[URLValuePreprocessorCallable]]

A data structure of functions to call to modify the keyword arguments passed to the view function, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests.

To register a function, use the url_value_preprocessor() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

view_functions: t.Dict[str, t.Callable]

A dictionary mapping endpoint names to view functions.

To register a view function, use the route() decorator.

This data structure is internal. It should not be modified directly and its format may change at any time.

Incoming Request Data

class flask.Request(environ: WSGIEnvironment, populate_request: bool = True, shallow: bool = False)

The request object used by default in Flask. Remembers the matched endpoint and view arguments.

It is what ends up as request. If you want to replace the request object used you can subclass this and set request_class to your subclass.

The request object is a Request subclass and provides all of the attributes Werkzeug defines plus a few Flask specific ones.

environ

The underlying WSGI environment.

path
full_path
script_root
url
base_url
url_root

Provides different ways to look at the current RFC 3987. Imagine your application is listening on the following application root:

http://www.example.com/myapplication

And a user requests the following URI:

http://www.example.com/myapplication/%CF%80/page.html?x=y

In this case the values of the above mentioned attributes would be the following:

path

u'/π/page.html'

full_path

u'/π/page.html?x=y'

script_root

u'/myapplication'

base_url

u'http://www.example.com/myapplication/π/page.html'

url

u'http://www.example.com/myapplication/π/page.html?x=y'

url_root

u'http://www.example.com/myapplication/'

property accept_charsets: werkzeug.datastructures.CharsetAccept

List of charsets this client supports as CharsetAccept object.

property accept_encodings: werkzeug.datastructures.Accept

List of encodings this client accepts. Encodings in a HTTP term are compression encodings such as gzip. For charsets have a look at accept_charset.

property accept_languages: werkzeug.datastructures.LanguageAccept

List of languages this client accepts as LanguageAccept object.

property accept_mimetypes: werkzeug.datastructures.MIMEAccept

List of mimetypes this client supports as MIMEAccept object.

access_control_request_headers

Sent with a preflight request to indicate which headers will be sent with the cross origin request. Set access_control_allow_headers on the response to indicate which headers are allowed.

access_control_request_method

Sent with a preflight request to indicate which method will be used for the cross origin request. Set access_control_allow_methods on the response to indicate which methods are allowed.

property access_route: List[str]

If a forwarded header exists this is a list of all ip addresses from the client ip to the last proxy server.

classmethod application(f: Callable[[Request], WSGIApplication]) WSGIApplication

Decorate a function as responder that accepts the request as the last argument. This works like the responder() decorator but the function is passed the request object as the last argument and the request object will be closed automatically:

@Request.application
def my_wsgi_app(request):
    return Response('Hello World!')

As of Werkzeug 0.14 HTTP exceptions are automatically caught and converted to responses instead of failing.

Parameters

f – the WSGI callable to decorate

Returns

a new WSGI callable

property args: werkzeug.datastructures.MultiDict[str, str]

The parsed URL parameters (the part in the URL after the question mark).

By default an ImmutableMultiDict is returned from this function. This can be changed by setting parameter_storage_class to a different type. This might be necessary if the order of the form data is important.

property authorization: Optional[werkzeug.datastructures.Authorization]

The Authorization object in parsed form.

property base_url: str

Like url but without the query string.

property blueprint: Optional[str]

The registered name of the current blueprint.

This will be None if the endpoint is not part of a blueprint, or if URL matching failed or has not been performed yet.

This does not necessarily match the name the blueprint was created with. It may have been nested, or registered with a different name.

property blueprints: List[str]

The registered names of the current blueprint upwards through parent blueprints.

This will be an empty list if there is no current blueprint, or if URL matching failed.

New in version 2.0.1.

property cache_control: werkzeug.datastructures.RequestCacheControl

A RequestCacheControl object for the incoming cache control headers.

close() None

Closes associated resources of this request object. This closes all file handles explicitly. You can also use the request object in a with statement which will automatically close it.

New in version 0.9.

content_encoding

The Content-Encoding entity-header field is used as a modifier to the media-type. When present, its value indicates what additional content codings have been applied to the entity-body, and thus what decoding mechanisms must be applied in order to obtain the media-type referenced by the Content-Type header field.

New in version 0.9.

property content_length: Optional[int]

The Content-Length entity-header field indicates the size of the entity-body in bytes or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.

content_md5

The Content-MD5 entity-header field, as defined in RFC 1864, is an MD5 digest of the entity-body for the purpose of providing an end-to-end message integrity check (MIC) of the entity-body. (Note: a MIC is good for detecting accidental modification of the entity-body in transit, but is not proof against malicious attacks.)

New in version 0.9.

content_type

The Content-Type entity-header field indicates the media type of the entity-body sent to the recipient or, in the case of the HEAD method, the media type that would have been sent had the request been a GET.

property cookies: werkzeug.datastructures.ImmutableMultiDict[str, str]

A dict with the contents of all cookies transmitted with the request.

property data: bytes

Contains the incoming request data as string in case it came with a mimetype Werkzeug does not handle.

date

The Date general-header field represents the date and time at which the message was originated, having the same semantics as orig-date in RFC 822.

Changed in version 2.0: The datetime object is timezone-aware.

dict_storage_class

alias of werkzeug.datastructures.ImmutableMultiDict

property endpoint: Optional[str]

The endpoint that matched the request URL.

This will be None if matching failed or has not been performed yet.

This in combination with view_args can be used to reconstruct the same URL or a modified URL.

environ: WSGIEnvironment

The WSGI environment containing HTTP headers and information from the WSGI server.

property files: werkzeug.datastructures.ImmutableMultiDict[str, werkzeug.datastructures.FileStorage]

MultiDict object containing all uploaded files. Each key in files is the name from the <input type="file" name="">. Each value in files is a Werkzeug FileStorage object.

It basically behaves like a standard file object you know from Python, with the difference that it also has a save() function that can store the file on the filesystem.

Note that files will only contain data if the request method was POST, PUT or PATCH and the <form> that posted to the request had enctype="multipart/form-data". It will be empty otherwise.

See the MultiDict / FileStorage documentation for more details about the used data structure.

property form: werkzeug.datastructures.ImmutableMultiDict[str, str]

The form parameters. By default an ImmutableMultiDict is returned from this function. This can be changed by setting parameter_storage_class to a different type. This might be necessary if the order of the form data is important.

Please keep in mind that file uploads will not end up here, but instead in the files attribute.

Changed in version 0.9: Previous to Werkzeug 0.9 this would only contain form data for POST and PUT requests.

form_data_parser_class

alias of werkzeug.formparser.FormDataParser

classmethod from_values(*args: Any, **kwargs: Any) werkzeug.wrappers.request.Request

Create a new request object based on the values provided. If environ is given missing values are filled from there. This method is useful for small scripts when you need to simulate a request from an URL. Do not use this method for unittesting, there is a full featured client object (Client) that allows to create multipart requests, support for cookies etc.

This accepts the same options as the EnvironBuilder.

Changed in version 0.5: This method now accepts the same arguments as EnvironBuilder. Because of this the environ parameter is now called environ_overrides.

Returns

request object

property full_path: str

Requested path, including the query string.

get_data(cache: bool = True, as_text: bool = False, parse_form_data: bool = False) Union[bytes, str]

This reads the buffered incoming data from the client into one bytes object. By default this is cached but that behavior can be changed by setting cache to False.

Usually it’s a bad idea to call this method without checking the content length first as a client could send dozens of megabytes or more to cause memory problems on the server.

Note that if the form data was already parsed this method will not return anything as form data parsing does not cache the data like this method does. To implicitly invoke form data parsing function set parse_form_data to True. When this is done the return value of this method will be an empty string if the form parser handles the data. This generally is not necessary as if the whole data is cached (which is the default) the form parser will used the cached data to parse the form data. Please be generally aware of checking the content length first in any case before calling this method to avoid exhausting server memory.

If as_text is set to True the return value will be a decoded string.

New in version 0.9.

get_json(force: bool = False, silent: bool = False, cache: bool = True) Optional[Any]

Parse data as JSON.

If the mimetype does not indicate JSON (application/json, see is_json), or parsing fails, on_json_loading_failed() is called and its return value is used as the return value. By default this raises a 400 Bad Request error.

Parameters
  • force – Ignore the mimetype and always try to parse JSON.

  • silent – Silence mimetype and parsing errors, and return None instead.

  • cache – Store the parsed JSON to return for subsequent calls.

Changed in version 2.1: Raise a 400 error if the content type is incorrect.

headers

The headers received with the request.

property host: str

The host name the request was made to, including the port if it’s non-standard. Validated with trusted_hosts.

property host_url: str

The request URL scheme and host only.

property if_match: werkzeug.datastructures.ETags

An object containing all the etags in the If-Match header.

Return type

ETags

property if_modified_since: Optional[datetime.datetime]

The parsed If-Modified-Since header as a datetime object.

Changed in version 2.0: The datetime object is timezone-aware.

property if_none_match: werkzeug.datastructures.ETags

An object containing all the etags in the If-None-Match header.

Return type

ETags

property if_range: werkzeug.datastructures.IfRange

The parsed If-Range header.

Changed in version 2.0: IfRange.date is timezone-aware.

New in version 0.7.

property if_unmodified_since: Optional[datetime.datetime]

The parsed If-Unmodified-Since header as a datetime object.

Changed in version 2.0: The datetime object is timezone-aware.

input_stream

The WSGI input stream.

In general it’s a bad idea to use this one because you can easily read past the boundary. Use the stream instead.

property is_json: bool

Check if the mimetype indicates JSON data, either application/json or application/*+json.

is_multiprocess

boolean that is True if the application is served by a WSGI server that spawns multiple processes.

is_multithread

boolean that is True if the application is served by a multithreaded WSGI server.

is_run_once

boolean that is True if the application will be executed only once in a process lifetime. This is the case for CGI for example, but it’s not guaranteed that the execution only happens one time.

property is_secure: bool

True if the request was made with a secure protocol (HTTPS or WSS).

property json: Optional[Any]

The parsed JSON data if mimetype indicates JSON (application/json, see is_json).

Calls get_json() with default arguments.

If the request content type is not application/json, this will raise a 400 Bad Request error.

Changed in version 2.1: Raise a 400 error if the content type is incorrect.

json_module = <module 'flask.json' from '/home/gruy/projects/rtfmd.com/rtfmd.com/.venv/lib/python3.10/site-packages/flask/json/__init__.py'>

A module or other object that has dumps and loads functions that match the API of the built-in json module.

list_storage_class

alias of werkzeug.datastructures.ImmutableList

make_form_data_parser() werkzeug.formparser.FormDataParser

Creates the form data parser. Instantiates the form_data_parser_class with some parameters.

New in version 0.8.

property max_content_length: Optional[int]

Read-only view of the MAX_CONTENT_LENGTH config key.

max_forwards

The Max-Forwards request-header field provides a mechanism with the TRACE and OPTIONS methods to limit the number of proxies or gateways that can forward the request to the next inbound server.

method

The method the request was made with, such as GET.

property mimetype: str

Like content_type, but without parameters (eg, without charset, type etc.) and always lowercase. For example if the content type is text/HTML; charset=utf-8 the mimetype would be 'text/html'.

property mimetype_params: Dict[str, str]

The mimetype parameters as dict. For example if the content type is text/html; charset=utf-8 the params would be {'charset': 'utf-8'}.

on_json_loading_failed(e: Optional[ValueError]) Any

Called if get_json() fails and isn’t silenced.

If this method returns a value, it is used as the return value for get_json(). The default implementation raises BadRequest.

Parameters

e – If parsing failed, this is the exception. It will be None if the content type wasn’t application/json.

origin

The host that the request originated from. Set access_control_allow_origin on the response to indicate which origins are allowed.

parameter_storage_class

alias of werkzeug.datastructures.ImmutableMultiDict

path

The path part of the URL after root_path. This is the path used for routing within the application.

property pragma: werkzeug.datastructures.HeaderSet

The Pragma general-header field is used to include implementation-specific directives that might apply to any recipient along the request/response chain. All pragma directives specify optional behavior from the viewpoint of the protocol; however, some systems MAY require that behavior be consistent with the directives.

query_string

The part of the URL after the “?”. This is the raw value, use args for the parsed values.

property range: Optional[werkzeug.datastructures.Range]

The parsed Range header.

New in version 0.7.

Return type

Range

referrer

The Referer[sic] request-header field allows the client to specify, for the server’s benefit, the address (URI) of the resource from which the Request-URI was obtained (the “referrer”, although the header field is misspelled).

remote_addr

The address of the client sending the request.

remote_user

If the server supports user authentication, and the script is protected, this attribute contains the username the user has authenticated as.

root_path

The prefix that the application is mounted under, without a trailing slash. path comes after this.

property root_url: str

The request URL scheme, host, and root path. This is the root that the application is accessed from.

routing_exception: Optional[Exception] = None

If matching the URL failed, this is the exception that will be raised / was raised as part of the request handling. This is usually a NotFound exception or something similar.

scheme

The URL scheme of the protocol the request used, such as https or wss.

property script_root: str

Alias for self.root_path. environ["SCRIPT_ROOT"] without a trailing slash.

server

The address of the server. (host, port), (path, None) for unix sockets, or None if not known.

shallow: bool

Set when creating the request object. If True, reading from the request body will cause a RuntimeException. Useful to prevent modifying the stream from middleware.

property stream: IO[bytes]

If the incoming form data was not encoded with a known mimetype the data is stored unmodified in this stream for consumption. Most of the time it is a better idea to use data which will give you that data as a string. The stream only returns the data once.

Unlike input_stream this stream is properly guarded that you can’t accidentally read past the length of the input. Werkzeug will internally always refer to this stream to read data which makes it possible to wrap this object with a stream that does filtering.

Changed in version 0.9: This stream is now always available but might be consumed by the form parser later on. Previously the stream was only set if no parsing happened.

property url: str

The full request URL with the scheme, host, root path, path, and query string.

property url_charset: str

The charset that is assumed for URLs. Defaults to the value of charset.

New in version 0.6.

property url_root: str

Alias for root_url. The URL with scheme, host, and root path. For example, https://example.com/app/.

url_rule: Optional[Rule] = None

The internal URL rule that matched the request. This can be useful to inspect which methods are allowed for the URL from a before/after handler (request.url_rule.methods) etc. Though if the request’s method was invalid for the URL rule, the valid list is available in routing_exception.valid_methods instead (an attribute of the Werkzeug exception MethodNotAllowed) because the request was never internally bound.

New in version 0.6.

property user_agent: werkzeug.user_agent.UserAgent

The user agent. Use user_agent.string to get the header value. Set user_agent_class to a subclass of UserAgent to provide parsing for the other properties or other extended data.

Changed in version 2.0: The built in parser is deprecated and will be removed in Werkzeug 2.1. A UserAgent subclass must be set to parse data from the string.

user_agent_class

alias of werkzeug.user_agent.UserAgent

property values: werkzeug.datastructures.CombinedMultiDict[str, str]

A werkzeug.datastructures.CombinedMultiDict that combines args and form.

For GET requests, only args are present, not form.

Changed in version 2.0: For GET requests, only args are present, not form.

view_args: Optional[Dict[str, Any]] = None

A dict of view arguments that matched the request. If an exception happened when matching, this will be None.

property want_form_data_parsed: bool

True if the request method carries content. By default this is true if a Content-Type is sent.

New in version 0.8.

flask.request

To access incoming request data, you can use the global request object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment.

This is a proxy. See Notes On Proxies for more information.

The request object is an instance of a Request subclass and provides all of the attributes Werkzeug defines. This just shows a quick overview of the most important ones.

Response Objects

class flask.Response(response: Optional[Union[Iterable[bytes], bytes, Iterable[str], str]] = None, status: Optional[Union[int, str, http.HTTPStatus]] = None, headers: Optional[Union[Mapping[str, Union[str, int, Iterable[Union[str, int]]]], Iterable[Tuple[str, Union[str, int]]]]] = None, mimetype: Optional[str] = None, content_type: Optional[str] = None, direct_passthrough: bool = False)

The response object that is used by default in Flask. Works like the response object from Werkzeug but is set to have an HTML mimetype by default. Quite often you don’t have to create this object yourself because make_response() will take care of that for you.

If you want to replace the response object used you can subclass this and set response_class to your subclass.

Changed in version 1.0: JSON support is added to the response, like the request. This is useful when testing to get the test client response data as JSON.

Changed in version 1.0: Added max_cookie_size.

headers

A Headers object representing the response headers.

status

A string with a response status.

status_code

The response status as integer.

property data: Union[bytes, str]

A descriptor that calls get_data() and set_data().

get_json(force: bool = False, silent: bool = False) Optional[Any]

Parse data as JSON. Useful during testing.

If the mimetype does not indicate JSON (application/json, see is_json), this returns None.

Unlike Request.get_json(), the result is not cached.

Parameters
  • force – Ignore the mimetype and always try to parse JSON.

  • silent – Silence parsing errors and return None instead.

property is_json: bool

Check if the mimetype indicates JSON data, either application/json or application/*+json.

Read-only view of the MAX_COOKIE_SIZE config key.

See max_cookie_size in Werkzeug’s docs.

property mimetype: Optional[str]

The mimetype (content type without charset etc.)

Sets a cookie.

A warning is raised if the size of the cookie header exceeds max_cookie_size, but the header will still be set.

Parameters
  • key – the key (name) of the cookie to be set.

  • value – the value of the cookie.

  • max_age – should be a number of seconds, or None (default) if the cookie should last only as long as the client’s browser session.

  • expires – should be a datetime object or UNIX timestamp.

  • path – limits the cookie to a given path, per default it will span the whole domain.

  • domain – if you want to set a cross-domain cookie. For example, domain=".example.com" will set a cookie that is readable by the domain www.example.com, foo.example.com etc. Otherwise, a cookie will only be readable by the domain that set it.

  • secure – If True, the cookie will only be available via HTTPS.

  • httponly – Disallow JavaScript access to the cookie.

  • samesite – Limit the scope of the cookie to only be attached to requests that are “same-site”.

Sessions

If you have set Flask.secret_key (or configured it from SECRET_KEY) you can use sessions in Flask applications. A session makes it possible to remember information from one request to another. The way Flask does this is by using a signed cookie. The user can look at the session contents, but can’t modify it unless they know the secret key, so make sure to set that to something complex and unguessable.

To access the current session you can use the session object:

class flask.session

The session object works pretty much like an ordinary dict, with the difference that it keeps track of modifications.

This is a proxy. See Notes On Proxies for more information.

The following attributes are interesting:

new

True if the session is new, False otherwise.

modified

True if the session object detected a modification. Be advised that modifications on mutable structures are not picked up automatically, in that situation you have to explicitly set the attribute to True yourself. Here an example:

# this change is not picked up because a mutable object (here
# a list) is changed.
session['objects'].append(42)
# so mark it as modified yourself
session.modified = True
permanent

If set to True the session lives for permanent_session_lifetime seconds. The default is 31 days. If set to False (which is the default) the session will be deleted when the user closes the browser.

Session Interface

New in version 0.8.

The session interface provides a simple way to replace the session implementation that Flask is using.

class flask.sessions.SessionInterface

The basic interface you have to implement in order to replace the default session interface which uses werkzeug’s securecookie implementation. The only methods you have to implement are open_session() and save_session(), the others have useful defaults which you don’t need to change.

The session object returned by the open_session() method has to provide a dictionary like interface plus the properties and methods from the SessionMixin. We recommend just subclassing a dict and adding that mixin:

class Session(dict, SessionMixin):
    pass

If open_session() returns None Flask will call into make_null_session() to create a session that acts as replacement if the session support cannot work because some requirement is not fulfilled. The default NullSession class that is created will complain that the secret key was not set.

To replace the session interface on an application all you have to do is to assign flask.Flask.session_interface:

app = Flask(__name__)
app.session_interface = MySessionInterface()

Multiple requests with the same session may be sent and handled concurrently. When implementing a new session interface, consider whether reads or writes to the backing store must be synchronized. There is no guarantee on the order in which the session for each request is opened or saved, it will occur in the order that requests begin and end processing.

New in version 0.8.

Returns the domain that should be set for the session cookie.

Uses SESSION_COOKIE_DOMAIN if it is configured, otherwise falls back to detecting the domain based on SERVER_NAME.

Once detected (or if not set at all), SESSION_COOKIE_DOMAIN is updated to avoid re-running the logic.

Returns True if the session cookie should be httponly. This currently just returns the value of the SESSION_COOKIE_HTTPONLY config var.

Returns the name of the session cookie.

Uses app.session_cookie_name which is set to SESSION_COOKIE_NAME

Returns the path for which the cookie should be valid. The default implementation uses the value from the SESSION_COOKIE_PATH config var if it’s set, and falls back to APPLICATION_ROOT or uses / if it’s None.

Return 'Strict' or 'Lax' if the cookie should use the SameSite attribute. This currently just returns the value of the SESSION_COOKIE_SAMESITE setting.

Returns True if the cookie should be secure. This currently just returns the value of the SESSION_COOKIE_SECURE setting.

get_expiration_time(app: Flask, session: flask.sessions.SessionMixin) Optional[datetime.datetime]

A helper method that returns an expiration date for the session or None if the session is linked to the browser session. The default implementation returns now + the permanent session lifetime configured on the application.

is_null_session(obj: object) bool

Checks if a given object is a null session. Null sessions are not asked to be saved.

This checks if the object is an instance of null_session_class by default.

make_null_session(app: Flask) flask.sessions.NullSession

Creates a null session which acts as a replacement object if the real session support could not be loaded due to a configuration error. This mainly aids the user experience because the job of the null session is to still support lookup without complaining but modifications are answered with a helpful error message of what failed.

This creates an instance of null_session_class by default.

null_session_class

make_null_session() will look here for the class that should be created when a null session is requested. Likewise the is_null_session() method will perform a typecheck against this type.

alias of flask.sessions.NullSession

open_session(app: Flask, request: Request) Optional[flask.sessions.SessionMixin]

This is called at the beginning of each request, after pushing the request context, before matching the URL.

This must return an object which implements a dictionary-like interface as well as the SessionMixin interface.

This will return None to indicate that loading failed in some way that is not immediately an error. The request context will fall back to using make_null_session() in this case.

pickle_based = False

A flag that indicates if the session interface is pickle based. This can be used by Flask extensions to make a decision in regards to how to deal with the session object.

New in version 0.10.

save_session(app: Flask, session: flask.sessions.SessionMixin, response: Response) None

This is called at the end of each request, after generating a response, before removing the request context. It is skipped if is_null_session() returns True.

Used by session backends to determine if a Set-Cookie header should be set for this session cookie for this response. If the session has been modified, the cookie is set. If the session is permanent and the SESSION_REFRESH_EACH_REQUEST config is true, the cookie is always set.

This check is usually skipped if the session was deleted.

New in version 0.11.

class flask.sessions.SecureCookieSessionInterface

The default session interface that stores sessions in signed cookies through the itsdangerous module.

static digest_method(string=b'', *, usedforsecurity=True)

the hash function to use for the signature. The default is sha1

key_derivation = 'hmac'

the name of the itsdangerous supported key derivation. The default is hmac.

open_session(app: Flask, request: Request) Optional[flask.sessions.SecureCookieSession]

This is called at the beginning of each request, after pushing the request context, before matching the URL.

This must return an object which implements a dictionary-like interface as well as the SessionMixin interface.

This will return None to indicate that loading failed in some way that is not immediately an error. The request context will fall back to using make_null_session() in this case.

salt = 'cookie-session'

the salt that should be applied on top of the secret key for the signing of cookie based sessions.

save_session(app: Flask, session: flask.sessions.SessionMixin, response: Response) None

This is called at the end of each request, after generating a response, before removing the request context. It is skipped if is_null_session() returns True.

serializer = <flask.json.tag.TaggedJSONSerializer object>

A python serializer for the payload. The default is a compact JSON derived serializer with support for some extra Python types such as datetime objects or tuples.

session_class

alias of flask.sessions.SecureCookieSession

class flask.sessions.SecureCookieSession(initial: Optional[Any] = None)

Base class for sessions based on signed cookies.

This session backend will set the modified and accessed attributes. It cannot reliably track whether a session is new (vs. empty), so new remains hard coded to False.

accessed = False

header, which allows caching proxies to cache different pages for different users.

get(key: str, default: Optional[Any] = None) Any

Return the value for key if key is in the dictionary, else default.

modified = False

When data is changed, this is set to True. Only the session dictionary itself is tracked; if the session contains mutable data (for example a nested dict) then this must be set to True manually when modifying that data. The session cookie will only be written to the response if this is True.

setdefault(key: str, default: Optional[Any] = None) Any

Insert key with a value of default if key is not in the dictionary.

Return the value for key if key is in the dictionary, else default.

class flask.sessions.NullSession(initial: Optional[Any] = None)

Class used to generate nicer error messages if sessions are not available. Will still allow read-only access to the empty session but fail on setting.

clear() None.  Remove all items from D.
pop(k[, d]) v, remove specified key and return the corresponding value.

If the key is not found, return the default if given; otherwise, raise a KeyError.

popitem(*args: Any, **kwargs: Any) te.NoReturn

Remove and return a (key, value) pair as a 2-tuple.

Pairs are returned in LIFO (last-in, first-out) order. Raises KeyError if the dict is empty.

setdefault(*args: Any, **kwargs: Any) te.NoReturn

Insert key with a value of default if key is not in the dictionary.

Return the value for key if key is in the dictionary, else default.

update([E, ]**F) None.  Update D from dict/iterable E and F.

If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v In either case, this is followed by: for k in F: D[k] = F[k]

class flask.sessions.SessionMixin

Expands a basic dictionary with session attributes.

accessed = True

Some implementations can detect when session data is read or written and set this when that happens. The mixin default is hard coded to True.

modified = True

Some implementations can detect changes to the session and set this when that happens. The mixin default is hard coded to True.

property permanent: bool

This reflects the '_permanent' key in the dict.

Notice

The PERMANENT_SESSION_LIFETIME config key can also be an integer starting with Flask 0.8. Either catch this down yourself or use the permanent_session_lifetime attribute on the app which converts the result to an integer automatically.

Test Client

class flask.testing.FlaskClient(*args: Any, **kwargs: Any)

Works like a regular Werkzeug test client but has some knowledge about how Flask works to defer the cleanup of the request context stack to the end of a with body when used in a with statement. For general information about how to use this class refer to werkzeug.test.Client.

Changed in version 0.12: app.test_client() includes preset default environment, which can be set after instantiation of the app.test_client() object in client.environ_base.

Basic usage is outlined in the Testing Flask Applications chapter.

open(*args: Any, buffered: bool = False, follow_redirects: bool = False, **kwargs: Any) TestResponse

Generate an environ dict from the given arguments, make a request to the application using it, and return the response.

Parameters
  • args – Passed to EnvironBuilder to create the environ for the request. If a single arg is passed, it can be an existing EnvironBuilder or an environ dict.

  • buffered – Convert the iterator returned by the app into a list. If the iterator has a close() method, it is called automatically.

  • follow_redirects – Make additional requests to follow HTTP redirects until a non-redirect status is returned. TestResponse.history lists the intermediate responses.

Changed in version 2.1: Removed the as_tuple parameter.

Changed in version 2.0: as_tuple is deprecated and will be removed in Werkzeug 2.1. Use TestResponse.request and request.environ instead.

Changed in version 2.0: The request input stream is closed when calling response.close(). Input streams for redirects are automatically closed.

Changed in version 0.5: If a dict is provided as file in the dict for the data parameter the content type has to be called content_type instead of mimetype. This change was made for consistency with werkzeug.FileWrapper.

Changed in version 0.5: Added the follow_redirects parameter.

session_transaction(*args: Any, **kwargs: Any) Generator[flask.sessions.SessionMixin, None, None]

When used in combination with a with statement this opens a session transaction. This can be used to modify the session that the test client uses. Once the with block is left the session is stored back.

with client.session_transaction() as session:
    session['value'] = 42

Internally this is implemented by going through a temporary test request context and since session handling could depend on request variables this function accepts the same arguments as test_request_context() which are directly passed through.

Test CLI Runner

class flask.testing.FlaskCliRunner(app: Flask, **kwargs: Any)

A CliRunner for testing a Flask app’s CLI commands. Typically created using test_cli_runner(). See Testing CLI Commands.

invoke(cli: Optional[Any] = None, args: Optional[Any] = None, **kwargs: Any) Any

Invokes a CLI command in an isolated environment. See CliRunner.invoke for full method documentation. See Testing CLI Commands for examples.

If the obj argument is not given, passes an instance of ScriptInfo that knows how to load the Flask app being tested.

Parameters
  • cli – Command object to invoke. Default is the app’s cli group.

  • args – List of strings to invoke the command with.

Returns

a Result object.

Application Globals

To share data that is valid for one request only from one function to another, a global variable is not good enough because it would break in threaded environments. Flask provides you with a special object that ensures it is only valid for the active request and that will return different values for each request. In a nutshell: it does the right thing, like it does for request and session.

flask.g

A namespace object that can store data during an application context. This is an instance of Flask.app_ctx_globals_class, which defaults to ctx._AppCtxGlobals.

This is a good place to store resources during a request. During testing, you can use the Faking Resources and Context pattern to pre-configure such resources.

This is a proxy. See Notes On Proxies for more information.

Changed in version 0.10: Bound to the application context instead of the request context.

class flask.ctx._AppCtxGlobals

A plain object. Used as a namespace for storing data during an application context.

Creating an app context automatically creates this object, which is made available as the g proxy.

'key' in g

Check whether an attribute is present.

New in version 0.10.

iter(g)

Return an iterator over the attribute names.

New in version 0.10.

get(name: str, default: Optional[Any] = None) Any

Get an attribute by name, or a default value. Like dict.get().

Parameters
  • name – Name of attribute to get.

  • default – Value to return if the attribute is not present.

New in version 0.10.

pop(name: str, default: typing.Any = <object object>) Any

Get and remove an attribute by name. Like dict.pop().

Parameters
  • name – Name of attribute to pop.

  • default – Value to return if the attribute is not present, instead of raising a KeyError.

New in version 0.11.

setdefault(name: str, default: Optional[Any] = None) Any

Get the value of an attribute if it is present, otherwise set and return a default value. Like dict.setdefault().

Parameters
  • name – Name of attribute to get.

  • default – Value to set and return if the attribute is not present.

New in version 0.11.

Useful Functions and Classes

flask.current_app

A proxy to the application handling the current request. This is useful to access the application without needing to import it, or if it can’t be imported, such as when using the application factory pattern or in blueprints and extensions.

This is only available when an application context is pushed. This happens automatically during requests and CLI commands. It can be controlled manually with app_context().

This is a proxy. See Notes On Proxies for more information.

flask.has_request_context() bool

If you have code that wants to test if a request context is there or not this function can be used. For instance, you may want to take advantage of request information if the request object is available, but fail silently if it is unavailable.

class User(db.Model):

    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and has_request_context():
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

Alternatively you can also just test any of the context bound objects (such as request or g) for truthness:

class User(db.Model):

    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and request:
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

New in version 0.7.

flask.copy_current_request_context(f: Callable) Callable

A helper function that decorates a function to retain the current request context. This is useful when working with greenlets. The moment the function is decorated a copy of the request context is created and then pushed when the function is called. The current session is also included in the copied request context.

Example:

import gevent
from flask import copy_current_request_context

@app.route('/')
def index():
    @copy_current_request_context
    def do_some_work():
        # do some work here, it can access flask.request or
        # flask.session like you would otherwise in the view function.
        ...
    gevent.spawn(do_some_work)
    return 'Regular response'

New in version 0.10.

flask.has_app_context() bool

Works like has_request_context() but for the application context. You can also just do a boolean check on the current_app object instead.

New in version 0.9.

flask.url_for(endpoint: str, **values: Any) str

Generates a URL to the given endpoint with the method provided.

Variable arguments that are unknown to the target endpoint are appended to the generated URL as query arguments. If the value of a query argument is None, the whole pair is skipped. In case blueprints are active you can shortcut references to the same blueprint by prefixing the local endpoint with a dot (.).

This will reference the index function local to the current blueprint:

url_for('.index')

See URL Building.

Configuration values APPLICATION_ROOT and SERVER_NAME are only used when generating URLs outside of a request context.

To integrate applications, Flask has a hook to intercept URL build errors through Flask.url_build_error_handlers. The url_for function results in a BuildError when the current app does not have a URL for the given endpoint and values. When it does, the current_app calls its url_build_error_handlers if it is not None, which can return a string to use as the result of url_for (instead of url_for’s default to raise the BuildError exception) or re-raise the exception. An example:

def external_url_handler(error, endpoint, values):
    "Looks up an external URL when `url_for` cannot build a URL."
    # This is an example of hooking the build_error_handler.
    # Here, lookup_url is some utility function you've built
    # which looks up the endpoint in some external URL registry.
    url = lookup_url(endpoint, **values)
    if url is None:
        # External lookup did not have a URL.
        # Re-raise the BuildError, in context of original traceback.
        exc_type, exc_value, tb = sys.exc_info()
        if exc_value is error:
            raise exc_type(exc_value).with_traceback(tb)
        else:
            raise error
    # url_for will use this result, instead of raising BuildError.
    return url

app.url_build_error_handlers.append(external_url_handler)

Here, error is the instance of BuildError, and endpoint and values are the arguments passed into url_for. Note that this is for building URLs outside the current application, and not for handling 404 NotFound errors.

New in version 0.10: The _scheme parameter was added.

New in version 0.9: The _anchor and _method parameters were added.

New in version 0.9: Calls Flask.handle_build_error() on BuildError.

Parameters
  • endpoint – the endpoint of the URL (name of the function)

  • values – the variable arguments of the URL rule

  • _external – if set to True, an absolute URL is generated. Server address can be changed via SERVER_NAME configuration variable which falls back to the Host header, then to the IP and port of the request.

  • _scheme – a string specifying the desired URL scheme. The _external parameter must be set to True or a ValueError is raised. The default behavior uses the same scheme as the current request, or PREFERRED_URL_SCHEME if no request context is available. This also can be set to an empty string to build protocol-relative URLs.

  • _anchor – if provided this is added as anchor to the URL.

  • _method – if provided this explicitly specifies an HTTP method.

flask.abort(status: Union[int, Response], *args: Any, **kwargs: Any) te.NoReturn

Raises an HTTPException for the given status code or WSGI application.

If a status code is given, it will be looked up in the list of exceptions and will raise that exception. If passed a WSGI application, it will wrap it in a proxy WSGI exception and raise that:

abort(404)  # 404 Not Found
abort(Response('Hello World'))
flask.redirect(location: str, code: int = 302, Response: Optional[Type[Response]] = None) Response

Returns a response object (a WSGI application) that, if called, redirects the client to the target location. Supported codes are 301, 302, 303, 305, 307, and 308. 300 is not supported because it’s not a real redirect and 304 because it’s the answer for a request with a request with defined If-Modified-Since headers.

New in version 0.6: The location can now be a unicode string that is encoded using the iri_to_uri() function.

New in version 0.10: The class used for the Response object can now be passed in.

Parameters
  • location – the location the response should redirect to.

  • code – the redirect status code. defaults to 302.

  • Response (class) – a Response class to use when instantiating a response. The default is werkzeug.wrappers.Response if unspecified.

flask.make_response(*args: Any) Response

Sometimes it is necessary to set additional headers in a view. Because views do not have to return response objects but can return a value that is converted into a response object by Flask itself, it becomes tricky to add headers to it. This function can be called instead of using a return and you will get a response object which you can use to attach headers.

If view looked like this and you want to add a new header:

def index():
    return render_template('index.html', foo=42)

You can now do something like this:

def index():
    response = make_response(render_template('index.html', foo=42))
    response.headers['X-Parachutes'] = 'parachutes are cool'
    return response

This function accepts the very same arguments you can return from a view function. This for example creates a response with a 404 error code:

response = make_response(render_template('not_found.html'), 404)

The other use case of this function is to force the return value of a view function into a response which is helpful with view decorators:

response = make_response(view_function())
response.headers['X-Parachutes'] = 'parachutes are cool'

Internally this function does the following things:

New in version 0.6.

flask.after_this_request(f: Callable[[Response], Response]) Callable[[Response], Response]

Executes a function after this request. This is useful to modify response objects. The function is passed the response object and has to return the same or a new one.

Example:

@app.route('/')
def index():
    @after_this_request
    def add_header(response):
        response.headers['X-Foo'] = 'Parachute'
        return response
    return 'Hello World!'

This is more useful if a function other than the view function wants to modify a response. For instance think of a decorator that wants to add some headers without converting the return value into a response object.

New in version 0.9.

flask.send_file(path_or_file: Union[os.PathLike, str, BinaryIO], mimetype: Optional[str] = None, as_attachment: bool = False, download_name: Optional[str] = None, attachment_filename: Optional[str] = None, conditional: bool = True, etag: Union[bool, str] = True, add_etags: Optional[bool] = None, last_modified: Optional[Union[datetime.datetime, int, float]] = None, max_age: Optional[Union[int, Callable[[Optional[str]], Optional[int]]]] = None, cache_timeout: Optional[int] = None)

Send the contents of a file to the client.

The first argument can be a file path or a file-like object. Paths are preferred in most cases because Werkzeug can manage the file and get extra information from the path. Passing a file-like object requires that the file is opened in binary mode, and is mostly useful when building a file in memory with io.BytesIO.

Never pass file paths provided by a user. The path is assumed to be trusted, so a user could craft a path to access a file you didn’t intend. Use send_from_directory() to safely serve user-requested paths from within a directory.

If the WSGI server sets a file_wrapper in environ, it is used, otherwise Werkzeug’s built-in wrapper is used. Alternatively, if the HTTP server supports X-Sendfile, configuring Flask with USE_X_SENDFILE = True will tell the server to send the given path, which is much more efficient than reading it in Python.

Parameters
  • path_or_file – The path to the file to send, relative to the current working directory if a relative path is given. Alternatively, a file-like object opened in binary mode. Make sure the file pointer is seeked to the start of the data.

  • mimetype – The MIME type to send for the file. If not provided, it will try to detect it from the file name.

  • as_attachment – Indicate to a browser that it should offer to save the file instead of displaying it.

  • download_name – The default name browsers will use when saving the file. Defaults to the passed file name.

  • conditional – Enable conditional and range responses based on request headers. Requires passing a file path and environ.

  • etag – Calculate an ETag for the file, which requires passing a file path. Can also be a string to use instead.

  • last_modified – The last modified time to send for the file, in seconds. If not provided, it will try to detect it from the file path.

  • max_age – How long the client should cache the file, in seconds. If set, Cache-Control will be public, otherwise it will be no-cache to prefer conditional caching.

Changed in version 2.0: download_name replaces the attachment_filename parameter. If as_attachment=False, it is passed with Content-Disposition: inline instead.

Changed in version 2.0: max_age replaces the cache_timeout parameter. conditional is enabled and max_age is not set by default.

Changed in version 2.0: etag replaces the add_etags parameter. It can be a string to use instead of generating one.

Changed in version 2.0: Passing a file-like object that inherits from TextIOBase will raise a ValueError rather than sending an empty file.

New in version 2.0: Moved the implementation to Werkzeug. This is now a wrapper to pass some Flask-specific arguments.

Changed in version 1.1: filename may be a PathLike object.

Changed in version 1.1: Passing a BytesIO object supports range requests.

Changed in version 1.0.3: Filenames are encoded with ASCII instead of Latin-1 for broader compatibility with WSGI servers.

Changed in version 1.0: UTF-8 filenames as specified in RFC 2231 are supported.

Changed in version 0.12: The filename is no longer automatically inferred from file objects. If you want to use automatic MIME and etag support, pass a filename via filename_or_fp or attachment_filename.

Changed in version 0.12: attachment_filename is preferred over filename for MIME detection.

Changed in version 0.9: cache_timeout defaults to Flask.get_send_file_max_age().

Changed in version 0.7: MIME guessing and etag support for file-like objects was deprecated because it was unreliable. Pass a filename if you are able to, otherwise attach an etag yourself.

Changed in version 0.5: The add_etags, cache_timeout and conditional parameters were added. The default behavior is to add etags.

New in version 0.2.

flask.send_from_directory(directory: Union[os.PathLike, str], path: Union[os.PathLike, str], filename: Optional[str] = None, **kwargs: Any) Response

Send a file from within a directory using send_file().

@app.route("/uploads/<path:name>")
def download_file(name):
    return send_from_directory(
        app.config['UPLOAD_FOLDER'], name, as_attachment=True
    )

This is a secure way to serve files from a folder, such as static files or uploads. Uses safe_join() to ensure the path coming from the client is not maliciously crafted to point outside the specified directory.

If the final path does not point to an existing regular file, raises a 404 NotFound error.

Parameters
  • directory – The directory that path must be located under.

  • path – The path to the file to send, relative to directory.

  • kwargs – Arguments to pass to send_file().

Changed in version 2.0: path replaces the filename parameter.

New in version 2.0: Moved the implementation to Werkzeug. This is now a wrapper to pass some Flask-specific arguments.

New in version 0.5.

flask.escape()

Replace the characters &, <, >, ', and " in the string with HTML-safe sequences. Use this if you need to display text that might contain such characters in HTML.

If the object has an __html__ method, it is called and the return value is assumed to already be safe for HTML.

Parameters

s – An object to be converted to a string and escaped.

Returns

A Markup string with the escaped text.

class flask.Markup(base: Any = '', encoding: Optional[str] = None, errors: str = 'strict')

A string that is ready to be safely inserted into an HTML or XML document, either because it was escaped or because it was marked safe.

Passing an object to the constructor converts it to text and wraps it to mark it safe without escaping. To escape the text, use the escape() class method instead.

>>> Markup("Hello, <em>World</em>!")
Markup('Hello, <em>World</em>!')
>>> Markup(42)
Markup('42')
>>> Markup.escape("Hello, <em>World</em>!")
Markup('Hello &lt;em&gt;World&lt;/em&gt;!')

This implements the __html__() interface that some frameworks use. Passing an object that implements __html__() will wrap the output of that method, marking it safe.

>>> class Foo:
...     def __html__(self):
...         return '<a href="/foo">foo</a>'
...
>>> Markup(Foo())
Markup('<a href="/foo">foo</a>')

This is a subclass of str. It has the same methods, but escapes their arguments and returns a Markup instance.

>>> Markup("<em>%s</em>") % ("foo & bar",)
Markup('<em>foo &amp; bar</em>')
>>> Markup("<em>Hello</em> ") + "<foo>"
Markup('<em>Hello</em> &lt;foo&gt;')
classmethod escape(s: Any) markupsafe.Markup

Escape a string. Calls escape() and ensures that for subclasses the correct type is returned.

striptags() str

unescape() the markup, remove tags, and normalize whitespace to single spaces.

>>> Markup("Main &raquo;        <em>About</em>").striptags()
'Main » About'
unescape() str

Convert escaped markup back into a text string. This replaces HTML entities with the characters they represent.

>>> Markup("Main &raquo; <em>About</em>").unescape()
'Main » <em>About</em>'

Message Flashing

flask.flash(message: str, category: str = 'message') None

Flashes a message to the next request. In order to remove the flashed message from the session and to display it to the user, the template has to call get_flashed_messages().

Changed in version 0.3: category parameter added.

Parameters
  • message – the message to be flashed.

  • category – the category for the message. The following values are recommended: 'message' for any kind of message, 'error' for errors, 'info' for information messages and 'warning' for warnings. However any kind of string can be used as category.

flask.get_flashed_messages(with_categories: bool = False, category_filter: Iterable[str] = ()) Union[List[str], List[Tuple[str, str]]]

Pulls all flashed messages from the session and returns them. Further calls in the same request to the function will return the same messages. By default just the messages are returned, but when with_categories is set to True, the return value will be a list of tuples in the form (category, message) instead.

Filter the flashed messages to one or more categories by providing those categories in category_filter. This allows rendering categories in separate html blocks. The with_categories and category_filter arguments are distinct:

  • with_categories controls whether categories are returned with message text (True gives a tuple, where False gives just the message text).

  • category_filter filters the messages down to only those matching the provided categories.

See Message Flashing for examples.

Changed in version 0.3: with_categories parameter added.

Changed in version 0.9: category_filter parameter added.

Parameters
  • with_categories – set to True to also receive categories.

  • category_filter – filter of categories to limit return values. Only categories in the list will be returned.

JSON Support

Flask uses simplejson for the JSON implementation. Since simplejson is provided by both the standard library as well as extension, Flask will try simplejson first and then fall back to the stdlib json module. On top of that it will delegate access to the current application’s JSON encoders and decoders for easier customization.

So for starters instead of doing:

try:
    import simplejson as json
except ImportError:
    import json

You can instead just do this:

from flask import json

For usage examples, read the json documentation in the standard library. The following extensions are by default applied to the stdlib’s JSON module:

  1. datetime objects are serialized as RFC 822 strings.

  2. Any object with an __html__ method (like Markup) will have that method called and then the return value is serialized as string.

The htmlsafe_dumps() function of this json module is also available as a filter called |tojson in Jinja2. Note that in versions of Flask prior to Flask 0.10, you must disable escaping with |safe if you intend to use |tojson output inside script tags. In Flask 0.10 and above, this happens automatically (but it’s harmless to include |safe anyway).

<script type=text/javascript>
    doSomethingWith({{ user.username|tojson|safe }});
</script>

Auto-Sort JSON Keys

The configuration variable JSON_SORT_KEYS (Configuration Handling) can be set to false to stop Flask from auto-sorting keys. By default sorting is enabled and outside of the app context sorting is turned on.

Notice that disabling key sorting can cause issues when using content based HTTP caches and Python’s hash randomization feature.

flask.json.jsonify(*args: Any, **kwargs: Any) Response

Serialize data to JSON and wrap it in a Response with the application/json mimetype.

Uses dumps() to serialize the data, but args and kwargs are treated as data rather than arguments to json.dumps().

  1. Single argument: Treated as a single value.

  2. Multiple arguments: Treated as a list of values. jsonify(1, 2, 3) is the same as jsonify([1, 2, 3]).

  3. Keyword arguments: Treated as a dict of values. jsonify(data=data, errors=errors) is the same as jsonify({"data": data, "errors": errors}).

  4. Passing both arguments and keyword arguments is not allowed as it’s not clear what should happen.

from flask import jsonify

@app.route("/users/me")
def get_current_user():
    return jsonify(
        username=g.user.username,
        email=g.user.email,
        id=g.user.id,
    )

Will return a JSON response like this:

{
  "username": "admin",
  "email": "admin@localhost",
  "id": 42
}

The default output omits indents and spaces after separators. In debug mode or if JSONIFY_PRETTYPRINT_REGULAR is True, the output will be formatted to be easier to read.

Changed in version 2.0.2: decimal.Decimal is supported by converting to a string.

Changed in version 0.11: Added support for serializing top-level arrays. This introduces a security risk in ancient browsers. See security-json.

New in version 0.2.

flask.json.dumps(obj: Any, app: Optional[Flask] = None, **kwargs: Any) str

Serialize an object to a string of JSON.

Takes the same arguments as the built-in json.dumps(), with some defaults from application configuration.

Parameters
  • obj – Object to serialize to JSON.

  • app – Use this app’s config instead of the active app context or defaults.

  • kwargs – Extra arguments passed to json.dumps().

Changed in version 2.0.2: decimal.Decimal is supported by converting to a string.

Changed in version 2.0: encoding is deprecated and will be removed in Flask 2.1.

Changed in version 1.0.3: app can be passed directly, rather than requiring an app context for configuration.

flask.json.dump(obj: Any, fp: IO[str], app: Optional[Flask] = None, **kwargs: Any) None

Serialize an object to JSON written to a file object.

Takes the same arguments as the built-in json.dump(), with some defaults from application configuration.

Parameters
  • obj – Object to serialize to JSON.

  • fp – File object to write JSON to.

  • app – Use this app’s config instead of the active app context or defaults.

  • kwargs – Extra arguments passed to json.dump().

Changed in version 2.0: Writing to a binary file, and the encoding argument, is deprecated and will be removed in Flask 2.1.

flask.json.loads(s: Union[str, bytes], app: Optional[Flask] = None, **kwargs: Any) Any

Deserialize an object from a string of JSON.

Takes the same arguments as the built-in json.loads(), with some defaults from application configuration.

Parameters
  • s – JSON string to deserialize.

  • app – Use this app’s config instead of the active app context or defaults.

  • kwargs – Extra arguments passed to json.loads().

Changed in version 2.0: encoding is deprecated and will be removed in Flask 2.1. The data must be a string or UTF-8 bytes.

Changed in version 1.0.3: app can be passed directly, rather than requiring an app context for configuration.

flask.json.load(fp: IO[str], app: Optional[Flask] = None, **kwargs: Any) Any

Deserialize an object from JSON read from a file object.

Takes the same arguments as the built-in json.load(), with some defaults from application configuration.

Parameters
  • fp – File object to read JSON from.

  • app – Use this app’s config instead of the active app context or defaults.

  • kwargs – Extra arguments passed to json.load().

Changed in version 2.0: encoding is deprecated and will be removed in Flask 2.1. The file must be text mode, or binary mode with UTF-8 bytes.

class flask.json.JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)

The default JSON encoder. Handles extra types compared to the built-in json.JSONEncoder.

Assign a subclass of this to flask.Flask.json_encoder or flask.Blueprint.json_encoder to override the default.

default(o: Any) Any

Convert o to a JSON serializable type. See json.JSONEncoder.default(). Python does not support overriding how basic types like str or list are serialized, they are handled before this method.

class flask.json.JSONDecoder(*, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, strict=True, object_pairs_hook=None)

The default JSON decoder.

This does not change any behavior from the built-in json.JSONDecoder.

Assign a subclass of this to flask.Flask.json_decoder or flask.Blueprint.json_decoder to override the default.

Tagged JSON

A compact representation for lossless serialization of non-standard JSON types. SecureCookieSessionInterface uses this to serialize the session data, but it may be useful in other places. It can be extended to support other types.

class flask.json.tag.TaggedJSONSerializer

Serializer that uses a tag system to compactly represent objects that are not JSON types. Passed as the intermediate serializer to itsdangerous.Serializer.

The following extra types are supported:

default_tags = [<class 'flask.json.tag.TagDict'>, <class 'flask.json.tag.PassDict'>, <class 'flask.json.tag.TagTuple'>, <class 'flask.json.tag.PassList'>, <class 'flask.json.tag.TagBytes'>, <class 'flask.json.tag.TagMarkup'>, <class 'flask.json.tag.TagUUID'>, <class 'flask.json.tag.TagDateTime'>]

Tag classes to bind when creating the serializer. Other tags can be added later using register().

dumps(value: Any) str

Tag the value and dump it to a compact JSON string.

loads(value: str) Any

Load data from a JSON string and deserialized any tagged objects.

register(tag_class: Type[flask.json.tag.JSONTag], force: bool = False, index: Optional[int] = None) None

Register a new tag with this serializer.

Parameters
  • tag_class – tag class to register. Will be instantiated with this serializer instance.

  • force – overwrite an existing tag. If false (default), a KeyError is raised.

  • index – index to insert the new tag in the tag order. Useful when the new tag is a special case of an existing tag. If None (default), the tag is appended to the end of the order.

Raises

KeyError – if the tag key is already registered and force is not true.

tag(value: Any) Dict[str, Any]

Convert a value to a tagged representation if necessary.

untag(value: Dict[str, Any]) Any

Convert a tagged representation back to the original type.

class flask.json.tag.JSONTag(serializer: flask.json.tag.TaggedJSONSerializer)

Base class for defining type tags for TaggedJSONSerializer.

check(value: Any) bool

Check if the given value should be tagged by this tag.

key: Optional[str] = None

The tag to mark the serialized object with. If None, this tag is only used as an intermediate step during tagging.

tag(value: Any) Any

Convert the value to a valid JSON type and add the tag structure around it.

to_json(value: Any) Any

Convert the Python object to an object that is a valid JSON type. The tag will be added later.

to_python(value: Any) Any

Convert the JSON representation back to the correct type. The tag will already be removed.

Let’s see an example that adds support for OrderedDict. Dicts don’t have an order in JSON, so to handle this we will dump the items as a list of [key, value] pairs. Subclass JSONTag and give it the new key ' od' to identify the type. The session serializer processes dicts first, so insert the new tag at the front of the order since OrderedDict must be processed before dict.

from flask.json.tag import JSONTag

class TagOrderedDict(JSONTag):
    __slots__ = ('serializer',)
    key = ' od'

    def check(self, value):
        return isinstance(value, OrderedDict)

    def to_json(self, value):
        return [[k, self.serializer.tag(v)] for k, v in iteritems(value)]

    def to_python(self, value):
        return OrderedDict(value)

app.session_interface.serializer.register(TagOrderedDict, index=0)

Template Rendering

flask.render_template(template_name_or_list: Union[str, jinja2.environment.Template, List[Union[str, jinja2.environment.Template]]], **context: Any) str

Renders a template from the template folder with the given context.

Parameters
  • template_name_or_list – the name of the template to be rendered, or an iterable with template names the first one existing will be rendered

  • context – the variables that should be available in the context of the template.

flask.render_template_string(source: str, **context: Any) str

Renders a template from the given template source string with the given context. Template variables will be autoescaped.

Parameters
  • source – the source code of the template to be rendered

  • context – the variables that should be available in the context of the template.

flask.get_template_attribute(template_name: str, attribute: str) Any

Loads a macro (or variable) a template exports. This can be used to invoke a macro from within Python code. If you for example have a template named _cider.html with the following contents:

{% macro hello(name) %}Hello {{ name }}!{% endmacro %}

You can access this from Python code like this:

hello = get_template_attribute('_cider.html', 'hello')
return hello('World')

New in version 0.2.

Parameters
  • template_name – the name of the template

  • attribute – the name of the variable of macro to access

Configuration

class flask.Config(root_path: str, defaults: Optional[dict] = None)

Works exactly like a dict but provides ways to fill it from files or special dictionaries. There are two common patterns to populate the config.

Either you can fill the config from a config file:

app.config.from_pyfile('yourconfig.cfg')

Or alternatively you can define the configuration options in the module that calls from_object() or provide an import path to a module that should be loaded. It is also possible to tell it to use the same module and with that provide the configuration values just before the call:

DEBUG = True
SECRET_KEY = 'development key'
app.config.from_object(__name__)

In both cases (loading from any Python file or loading from modules), only uppercase keys are added to the config. This makes it possible to use lowercase values in the config file for temporary values that are not added to the config or to define the config keys in the same file that implements the application.

Probably the most interesting way to load configurations is from an environment variable pointing to a file:

app.config.from_envvar('YOURAPPLICATION_SETTINGS')

In this case before launching the application you have to set this environment variable to the file you want to use. On Linux and OS X use the export statement:

export YOURAPPLICATION_SETTINGS='/path/to/config/file'

On windows use set instead.

Parameters
  • root_path – path to which files are read relative from. When the config object is created by the application, this is the application’s root_path.

  • defaults – an optional dictionary of default values

from_envvar(variable_name: str, silent: bool = False) bool

Loads a configuration from an environment variable pointing to a configuration file. This is basically just a shortcut with nicer error messages for this line of code:

app.config.from_pyfile(os.environ['YOURAPPLICATION_SETTINGS'])
Parameters
  • variable_name – name of the environment variable

  • silent – set to True if you want silent failure for missing files.

Returns

True if the file was loaded successfully.

from_file(filename: str, load: Callable[[IO[Any]], Mapping], silent: bool = False) bool

Update the values in the config from a file that is loaded using the load parameter. The loaded data is passed to the from_mapping() method.

import json
app.config.from_file("config.json", load=json.load)

import toml
app.config.from_file("config.toml", load=toml.load)
Parameters
  • filename – The path to the data file. This can be an absolute path or relative to the config root path.

  • load (Callable[[Reader], Mapping] where Reader implements a read method.) – A callable that takes a file handle and returns a mapping of loaded data from the file.

  • silent – Ignore the file if it doesn’t exist.

Returns

True if the file was loaded successfully.

New in version 2.0.

from_mapping(mapping: Optional[Mapping[str, Any]] = None, **kwargs: Any) bool

Updates the config like update() ignoring items with non-upper keys. :return: Always returns True.

New in version 0.11.

from_object(obj: Union[object, str]) None

Updates the values from the given object. An object can be of one of the following two types:

  • a string: in this case the object with that name will be imported

  • an actual object reference: that object is used directly

Objects are usually either modules or classes. from_object() loads only the uppercase attributes of the module/class. A dict object will not work with from_object() because the keys of a dict are not attributes of the dict class.

Example of module-based configuration:

app.config.from_object('yourapplication.default_config')
from yourapplication import default_config
app.config.from_object(default_config)

Nothing is done to the object before loading. If the object is a class and has @property attributes, it needs to be instantiated before being passed to this method.

You should not use this function to load the actual configuration but rather configuration defaults. The actual config should be loaded with from_pyfile() and ideally from a location not within the package because the package might be installed system wide.

See Development / Production for an example of class-based configuration using from_object().

Parameters

obj – an import name or object

from_prefixed_env(prefix: str = 'FLASK', *, loads: typing.Callable[[str], typing.Any] = <function loads>) bool

Load any environment variables that start with FLASK_, dropping the prefix from the env key for the config key. Values are passed through a loading function to attempt to convert them to more specific types than strings.

Keys are loaded in sorted() order.

The default loading function attempts to parse values as any valid JSON type, including dicts and lists.

Specific items in nested dicts can be set by separating the keys with double underscores (__). If an intermediate key doesn’t exist, it will be initialized to an empty dict.

Parameters
  • prefix – Load env vars that start with this prefix, separated with an underscore (_).

  • loads – Pass each string value to this function and use the returned value as the config value. If any error is raised it is ignored and the value remains a string. The default is json.loads().

New in version 2.1.

from_pyfile(filename: str, silent: bool = False) bool

Updates the values in the config from a Python file. This function behaves as if the file was imported as module with the from_object() function.

Parameters
  • filename – the filename of the config. This can either be an absolute filename or a filename relative to the root path.

  • silent – set to True if you want silent failure for missing files.

Returns

True if the file was loaded successfully.

New in version 0.7: silent parameter.

get_namespace(namespace: str, lowercase: bool = True, trim_namespace: bool = True) Dict[str, Any]

Returns a dictionary containing a subset of configuration options that match the specified namespace/prefix. Example usage:

app.config['IMAGE_STORE_TYPE'] = 'fs'
app.config['IMAGE_STORE_PATH'] = '/var/app/images'
app.config['IMAGE_STORE_BASE_URL'] = 'http://img.website.com'
image_store_config = app.config.get_namespace('IMAGE_STORE_')

The resulting dictionary image_store_config would look like:

{
    'type': 'fs',
    'path': '/var/app/images',
    'base_url': 'http://img.website.com'
}

This is often useful when configuration options map directly to keyword arguments in functions or class constructors.

Parameters
  • namespace – a configuration namespace

  • lowercase – a flag indicating if the keys of the resulting dictionary should be lowercase

  • trim_namespace – a flag indicating if the keys of the resulting dictionary should not include the namespace

New in version 0.11.

Stream Helpers

flask.stream_with_context(generator_or_function: Union[Iterator, Callable[[...], Iterator]]) Iterator

Request contexts disappear when the response is started on the server. This is done for efficiency reasons and to make it less likely to encounter memory leaks with badly written WSGI middlewares. The downside is that if you are using streamed responses, the generator cannot access request bound information any more.

This function however can help you keep the context around for longer:

from flask import stream_with_context, request, Response

@app.route('/stream')
def streamed_response():
    @stream_with_context
    def generate():
        yield 'Hello '
        yield request.args['name']
        yield '!'
    return Response(generate())

Alternatively it can also be used around a specific generator:

from flask import stream_with_context, request, Response

@app.route('/stream')
def streamed_response():
    def generate():
        yield 'Hello '
        yield request.args['name']
        yield '!'
    return Response(stream_with_context(generate()))

New in version 0.9.

Useful Internals

class flask.ctx.RequestContext(app: Flask, environ: dict, request: Optional[Request] = None, session: Optional[SessionMixin] = None)

The request context contains all request relevant information. It is created at the beginning of the request and pushed to the _request_ctx_stack and removed at the end of it. It will create the URL adapter and request object for the WSGI environment provided.

Do not attempt to use this class directly, instead use test_request_context() and request_context() to create this object.

When the request context is popped, it will evaluate all the functions registered on the application for teardown execution (teardown_request()).

The request context is automatically popped at the end of the request for you. In debug mode the request context is kept around if exceptions happen so that interactive debuggers have a chance to introspect the data. With 0.4 this can also be forced for requests that did not fail and outside of DEBUG mode. By setting 'flask._preserve_context' to True on the WSGI environment the context will not pop itself at the end of the request. This is used by the test_client() for example to implement the deferred cleanup functionality.

You might find this helpful for unittests where you need the information from the context local around for a little longer. Make sure to properly pop() the stack yourself in that situation, otherwise your unittests will leak memory.

copy() flask.ctx.RequestContext

Creates a copy of this request context with the same request object. This can be used to move a request context to a different greenlet. Because the actual request object is the same this cannot be used to move a request context to a different thread unless access to the request object is locked.

New in version 0.10.

Changed in version 1.1: The current session object is used instead of reloading the original data. This prevents flask.session pointing to an out-of-date object.

match_request() None

Can be overridden by a subclass to hook into the matching of the request.

pop(exc: typing.Optional[BaseException] = <object object>) None

Pops the request context and unbinds it by doing that. This will also trigger the execution of functions registered by the teardown_request() decorator.

Changed in version 0.9: Added the exc argument.

push() None

Binds the request context to the current context.

flask._request_ctx_stack

The internal LocalStack that holds RequestContext instances. Typically, the request and session proxies should be accessed instead of the stack. It may be useful to access the stack in extension code.

The following attributes are always present on each layer of the stack:

app

the active Flask application.

url_adapter

the URL adapter that was used to match the request.

request

the current request object.

session

the active session object.

g

an object with all the attributes of the flask.g object.

flashes

an internal cache for the flashed messages.

Example usage:

from flask import _request_ctx_stack

def get_session():
    ctx = _request_ctx_stack.top
    if ctx is not None:
        return ctx.session
class flask.ctx.AppContext(app: Flask)

The application context binds an application object implicitly to the current thread or greenlet, similar to how the RequestContext binds request information. The application context is also implicitly created if a request context is created but the application is not on top of the individual application context.

pop(exc: typing.Optional[BaseException] = <object object>) None

Pops the app context.

push() None

Binds the app context to the current context.

flask._app_ctx_stack

The internal LocalStack that holds AppContext instances. Typically, the current_app and g proxies should be accessed instead of the stack. Extensions can ac