flask.app.Flask

The WSGI server calls the Flask application object as the WSGI application. This calls :meth:`wsgi_app`, which can be wrapped to apply middleware.

Undocumented

Register a custom template filter. Works exactly like the :meth:`template_filter` decorator. :param name: the optional name of the filter, otherwise the function name will be used.

Register a custom template global function. Works exactly like the :meth:`template_global` decorator. .. versionadded:: 0.10 :param name: the optional name of the global function, otherwise the function name will be used.

Register a custom template test. Works exactly like the :meth:`template_test` decorator. .. versionadded:: 0.10 :param name: the optional name of the test, otherwise the function name will be used.

Register a rule for routing incoming requests and building URLs. The :meth:`route` decorator is a shortcut to call this with the ``view_func`` argument. These are equivalent: .. code-block:: python @app.route("/") def index(): ... .. code-block:: python def index(): ... app.add_url_rule("/", view_func=index) See :ref:`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 :meth:`endpoint` decorator. .. code-block:: python 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. :param rule: The URL rule string. :param endpoint: The endpoint name to associate with the rule and view function. Used when routing and building URLs. Defaults to ``view_func.__name__``. :param view_func: The view function to associate with the endpoint name. :param provide_automatic_options: Add the ``OPTIONS`` method and respond to ``OPTIONS`` requests automatically. :param options: Extra options passed to the :class:`~werkzeug.routing.Rule` object.

Create an :class:`~flask.ctx.AppContext`. Use as a ``with`` block to push the context, which will make :data:`current_app` point at this application. An application context is automatically pushed by :meth:`RequestContext.push() <flask.ctx.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 :doc:`/appcontext`. .. versionadded:: 0.9

Return a sync function that will run the coroutine function. .. code-block:: python result = app.async_to_sync(func)(*args, **kwargs) Override this method to change how the app converts async code to be synchronously callable. .. versionadded:: 2.0

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. .. versionadded:: 0.8

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. .. deprecated:: 2.2 Will be removed in Flask 2.3. Run setup code when creating the application instead. .. versionadded:: 0.8

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 :meth:`jinja_loader` function instead. The global loader dispatches between the loaders of the application and the individual blueprints. .. versionadded:: 0.7

Create the Jinja environment based on :attr:`jinja_options` and the various Jinja-related methods of the app. Changing :attr:`jinja_options` after this will have no effect. Also adds Flask-related globals and filters to the environment. .. versionchanged:: 0.11 ``Environment.auto_reload`` set in accordance with ``TEMPLATES_AUTO_RELOAD`` configuration option. .. versionadded:: 0.5

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. .. versionadded:: 0.6 .. versionchanged:: 0.9 This can now also be called without a request object when the URL adapter is created for the application context. .. versionchanged:: 1.0 :data:`SERVER_NAME` no longer implicitly enables subdomain matching. Use :attr:`subdomain_matching` instead.

Undocumented

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 :func:`make_response`. .. versionchanged:: 0.7 This no longer does the exception handling, this code was moved to the new :meth:`full_dispatch_request`.

Called right before the application context is popped. When handling a request, the application context is popped after the request context. See :meth:`do_teardown_request`. This calls all functions decorated with :meth:`teardown_appcontext`. Then the :data:`appcontext_tearing_down` signal is sent. This is called by :meth:`AppContext.pop() <flask.ctx.AppContext.pop>`. .. versionadded:: 0.9

Called after the request is dispatched and the response is returned, right before the request context is popped. This calls all functions decorated with :meth:`teardown_request`, and :meth:`Blueprint.teardown_request` if a blueprint handled the request. Finally, the :data:`request_tearing_down` signal is sent. This is called by :meth:`RequestContext.pop() <flask.ctx.RequestContext.pop>`, which may be delayed during testing to maintain access to resources. :param exc: An unhandled exception raised while dispatching the request. Detected from the current exception information if not passed. Passed to each teardown function. .. versionchanged:: 0.9 Added the ``exc`` argument.

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. .. versionadded:: 2.0

Undocumented

Given the return value from a view function this finalizes the request by converting it into a response and invoking the postprocessing functions. This is invoked for both normal request dispatching as well as error handlers. Because this means that it might be called as a result of a failure a special safe mode is available which can be enabled with the `from_error_handler` flag. If enabled, failures in response processing will be logged and otherwise ignored. :internal:

Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling. .. versionadded:: 0.7

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 :data:`got_request_exception` signal. If :attr:`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 :exc:`~werkzeug.exceptions.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``. .. versionchanged:: 1.1.0 Always passes the ``InternalServerError`` instance to the handler, setting ``original_exception`` to the unhandled error. .. versionchanged:: 1.1.0 ``after_request`` functions and other finalization is done even for the default 500 response when there is no handler. .. versionadded:: 0.3

Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response. .. versionchanged:: 1.0.3 ``RoutingException``, used internally for actions such as slash redirects during routing, is not passed to error handlers. .. versionchanged:: 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``. .. versionadded:: 0.3

Called by :meth:`.url_for` if a :exc:`~werkzeug.routing.BuildError` was raised. If this returns a value, it will be returned by ``url_for``, otherwise the error will be re-raised. Each function in :attr:`url_build_error_handlers` is called with ``error``, ``endpoint`` and ``values``. If a function returns ``None`` or raises a ``BuildError``, it is skipped. Otherwise, its return value is returned by ``url_for``. :param error: The active ``BuildError`` being handled. :param endpoint: The endpoint being built. :param values: The keyword arguments passed to ``url_for``.

This method is called whenever an exception occurs that should be handled. A special case is :class:`~werkzeug .exceptions.HTTPException` which is forwarded to the :meth:`handle_http_exception` method. This function will either return a response value or reraise the exception with the same traceback. .. versionchanged:: 1.0 Key errors raised from request data like ``form`` show the bad key in debug mode rather than a generic bad request message. .. versionadded:: 0.7

Injects the URL defaults for the given endpoint directly into the values dictionary passed. This is used internally and automatically called on URL building. .. versionadded:: 0.7

Iterates over all blueprints by the order they were registered. .. versionadded:: 0.11

Undocumented

Undocumented

Logs an exception. This is called by :meth:`handle_exception` if debugging is disabled and right before the handler is called. The default implementation logs the exception as error on the :attr:`logger`. .. versionadded:: 0.8

Create the object to assign to :attr:`aborter`. That object is called by :func:`flask.abort` to raise HTTP errors, and can be called directly as well. By default, this creates an instance of :attr:`aborter_class`, which defaults to :class:`werkzeug.exceptions.Aborter`. .. versionadded:: 2.2

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. .. versionadded:: 0.8

This method is called to create the default ``OPTIONS`` response. This can be changed through subclassing to change the default behavior of ``OPTIONS`` responses. .. versionadded:: 0.7

Convert the return value from a view function to an instance of :attr:`response_class`. :param 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. ``list`` A list that will be jsonify'd before being returned. ``generator`` or ``iterator`` A generator that returns ``str`` or ``bytes`` to be streamed as the response. ``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 :attr:`response_class` instance, ``status`` overwrites the exiting value and ``headers`` are extended. :attr:`response_class` The object is returned unchanged. other :class:`~werkzeug.wrappers.Response` class The object is coerced to :attr:`response_class`. :func:`callable` The function is called as a WSGI application. The result is used to create a response object. .. versionchanged:: 2.2 A generator will be converted to a streaming response. A list will be converted to a JSON response. .. versionchanged:: 1.1 A dict will be converted to a JSON response. .. versionchanged:: 0.9 Previously a tuple was interpreted as the arguments for the response object.

Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors. .. versionadded:: 0.11

Opens a resource from the application's instance folder (:attr:`instance_path`). Otherwise works like :meth:`open_resource`. Instance resources can also be opened for writing. :param resource: the name of the resource. To access resources within subfolders use forward slashes as separator. :param mode: resource file opening mode, default is 'rb'.

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

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 :meth:`after_request` decorated functions. .. versionchanged:: 0.5 As of Flask 0.5 the functions registered for after request execution are called in reverse order of registration. :param response: a :attr:`response_class` object. :return: a new response object or the same, has to be an instance of :attr:`response_class`.

Intercept routing exceptions and possibly do something else. In debug mode, intercept a routing redirect and replace it with an error if the body will be discarded. With modern Werkzeug this shouldn't occur, since it now uses a 308 status which tells the browser to resend the method and body. .. versionchanged:: 2.1 Don't intercept 307 and 308 redirects. :meta private: :internal:

Create a redirect response object. This is called by :func:`flask.redirect`, and can be called directly as well. :param location: The URL to redirect to. :param code: The status code for the redirect. .. versionadded:: 2.2 Moved from ``flask.redirect``, which calls this method.

Register a :class:`~flask.Blueprint` on the application. Keyword arguments passed to this method will override the defaults set on the blueprint. Calls the blueprint's :meth:`~flask.Blueprint.register` method after recording the blueprint in the application's :attr:`blueprints`. :param blueprint: The blueprint to register. :param url_prefix: Blueprint routes will be prefixed with this. :param subdomain: Blueprint routes will match on this subdomain. :param url_defaults: Blueprint routes will use these default values for view arguments. :param options: Additional keyword arguments are passed to :class:`~flask.blueprints.BlueprintSetupState`. They can be accessed in :meth:`~flask.Blueprint.record` callbacks. .. versionchanged:: 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``. .. versionadded:: 0.7

Create a :class:`~flask.ctx.RequestContext` representing a WSGI environment. Use a ``with`` block to push the context, which will make :data:`request` point at this request. See :doc:`/reqcontext`. Typically you should not call this from your own code. A request context is automatically pushed by the :meth:`wsgi_app` when handling a request. Use :meth:`test_request_context` to create an environment and context instead of this method. :param environ: a WSGI environment

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 :doc:`/deploying/index` for WSGI server recommendations. If the :attr:`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 :command:`flask` command line script's ``run`` support. .. admonition:: 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 :meth:`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. :param 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. :param port: the port of the webserver. Defaults to ``5000`` or the port defined in the ``SERVER_NAME`` config variable if present. :param debug: if given, enable or disable debug mode. See :attr:`debug`. :param load_dotenv: Load the nearest :file:`.env` and :file:`.flaskenv` files to set environment variables. Will also change the working directory to the directory containing the first file found. :param options: the options to be forwarded to the underlying Werkzeug server. See :func:`werkzeug.serving.run_simple` for more information. .. versionchanged:: 1.0 If installed, python-dotenv will be used to load environment variables from :file:`.env` and :file:`.flaskenv` files. The :envvar:`FLASK_DEBUG` environment variable will override :attr:`debug`. Threaded mode is enabled by default. .. versionchanged:: 0.10 The default port is now picked from the ``SERVER_NAME`` variable.

Returns ``True`` if autoescaping should be active for the given template name. If no template name is given, returns `True`. .. versionchanged:: 2.2 Autoescaping is now enabled by default for ``.svg`` files. .. versionadded:: 0.5

Undocumented

Undocumented

Registers a shell context processor function. .. versionadded:: 0.11

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. .. versionadded:: 0.10

Registers a function to be called when the application context is popped. The application context is typically popped after the request context for each request, at the end of CLI commands, or after a manually pushed context ends. .. code-block:: python with app.app_context(): ... When the ``with`` block exits (or ``ctx.pop()`` is called), the teardown functions are called just before the app context is made inactive. 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 :meth:`errorhandler` is registered, it will handle the exception and the teardown will not receive it. Teardown functions must avoid raising exceptions. If they execute code that might fail they must surround that code with a ``try``/``except`` block and log any errors. The return values of teardown functions are ignored. .. versionadded:: 0.9

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] :param name: the optional name of the filter, otherwise the function name will be used.

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 .. versionadded:: 0.10 :param name: the optional name of the global function, otherwise the function name will be used.

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 .. versionadded:: 0.10 :param name: the optional name of the test, otherwise the function name will be used.

Undocumented

Create a CLI runner for testing CLI commands. See :ref:`testing-cli`. Returns an instance of :attr:`test_cli_runner_class`, by default :class:`~flask.testing.FlaskCliRunner`. The Flask app object is passed as the first argument. .. versionadded:: 1.0

Creates a test client for this application. For information about unit testing head over to :doc:`/testing`. 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 :attr:`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 :attr:`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 :class:`~flask.testing.FlaskClient` for more information. .. versionchanged:: 0.4 added support for ``with`` block usage for the client. .. versionadded:: 0.7 The `use_cookies` parameter was added as well as the ability to override the client to be used by setting the :attr:`test_client_class` attribute. .. versionchanged:: 0.11 Added `**kwargs` to support passing additional keyword arguments to the constructor of :attr:`test_client_class`.

Create a :class:`~flask.ctx.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 :doc:`/reqcontext`. Use a ``with`` block to push the context, which will make :data:`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 :class:`~werkzeug.test.EnvironBuilder`, with some defaults from the application. See the linked Werkzeug docs for most of the available arguments. Flask-specific behavior is listed here. :param path: URL path being requested. :param base_url: Base URL where the app is being served, which ``path`` is relative to. If not given, built from :data:`PREFERRED_URL_SCHEME`, ``subdomain``, :data:`SERVER_NAME`, and :data:`APPLICATION_ROOT`. :param subdomain: Subdomain name to append to :data:`SERVER_NAME`. :param url_scheme: Scheme to use instead of :data:`PREFERRED_URL_SCHEME`. :param data: The request body, either as a string or a dict of form keys and values. :param json: If given, this is serialized as JSON and passed as ``data``. Also defaults ``content_type`` to ``application/json``. :param args: other positional arguments passed to :class:`~werkzeug.test.EnvironBuilder`. :param kwargs: other keyword arguments passed to :class:`~werkzeug.test.EnvironBuilder`.

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. .. versionchanged:: 1.0 Bad request errors are not trapped by default in debug mode. .. versionadded:: 0.8

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

Generate a URL to the given endpoint with the given values. This is called by :func:`flask.url_for`, and can be called directly as well. An *endpoint* is the name of a URL rule, usually added with :meth:`@app.route() <route>`, and usually the same name as the view function. A route defined in a :class:`~flask.Blueprint` will prepend the blueprint's name separated by a ``.`` to the endpoint. In some cases, such as email messages, you want URLs to include the scheme and domain, like ``https://example.com/hello``. When not in an active request, URLs will be external by default, but this requires setting :data:`SERVER_NAME` so Flask knows what domain to use. :data:`APPLICATION_ROOT` and :data:`PREFERRED_URL_SCHEME` should also be configured as needed. This config is only used when not in an active request. Functions can be decorated with :meth:`url_defaults` to modify keyword arguments before the URL is built. If building fails for some reason, such as an unknown endpoint or incorrect values, the app's :meth:`handle_url_build_error` method is called. If that returns a string, that is returned, otherwise a :exc:`~werkzeug.routing.BuildError` is raised. :param endpoint: The endpoint name associated with the URL to generate. If this starts with a ``.``, the current blueprint name (if any) will be used. :param _anchor: If given, append this as ``#anchor`` to the URL. :param _method: If given, generate the URL associated with this method for the endpoint. :param _scheme: If given, the URL will have this scheme if it is external. :param _external: If given, prefer the URL to be internal (False) or require it to be external (True). External URLs include the scheme and domain. When not in an active request, URLs are external by default. :param values: Values to use for the variable parts of the URL rule. Unknown keys are appended as query string arguments, like ``?a=b&c=d``. .. versionadded:: 2.2 Moved from ``flask.url_for``, which calls this method.

Undocumented

The actual WSGI application. This is not implemented in :meth:`__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. .. versionchanged:: 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 :ref:`callbacks-and-errors`. :param environ: A WSGI environment. :param start_response: A callable accepting a status code, a list of headers, and an optional exception context to start the response.