View Class — flask Architecture

Source Code

src/flask/views.py lines 16–135

class View:
    """Subclass this class and override :meth:`dispatch_request` to
    create a generic class-based view. Call :meth:`as_view` to create a
    view function that creates an instance of the class with the given
    arguments and calls its ``dispatch_request`` method with any URL
    variables.

    See :doc:`views` for a detailed guide.

    .. code-block:: python

        class Hello(View):
            init_every_request = False

            def dispatch_request(self, name):
                return f"Hello, {name}!"

        app.add_url_rule(
            "/hello/<name>", view_func=Hello.as_view("hello")
        )

    Set :attr:`methods` on the class to change what methods the view
    accepts.

    Set :attr:`decorators` on the class to apply a list of decorators to
    the generated view function. Decorators applied to the class itself
    will not be applied to the generated view function!

    Set :attr:`init_every_request` to ``False`` for efficiency, unless
    you need to store request-global data on ``self``.
    """

    #: The methods this view is registered for. Uses the same default
    #: (``["GET", "HEAD", "OPTIONS"]``) as ``route`` and
    #: ``add_url_rule`` by default.
    methods: t.ClassVar[t.Collection[str] | None] = None

    #: Control whether the ``OPTIONS`` method is handled automatically.
    #: Uses the same default (``True``) as ``route`` and
    #: ``add_url_rule`` by default.
    provide_automatic_options: t.ClassVar[bool | None] = None

    #: A list of decorators to apply, in order, to the generated view
    #: function. Remember that ``@decorator`` syntax is applied bottom
    #: to top, so the first decorator in the list would be the bottom
    #: decorator.
    #:
    #: .. versionadded:: 0.8
    decorators: t.ClassVar[list[t.Callable[..., t.Any]]] = []

    #: Create a new instance of this view class for every request by
    #: default. If a view subclass sets this to ``False``, the same
    #: instance is used for every request.
    #:
    #: A single instance is more efficient, especially if complex setup
    #: is done during init. However, storing data on ``self`` is no
    #: longer safe across requests, and :data:`~flask.g` should be used
    #: instead.
    #:
    #: .. versionadded:: 2.2
    init_every_request: t.ClassVar[bool] = True

    def dispatch_request(self) -> ft.ResponseReturnValue:
        """The actual view function behavior. Subclasses must override
        this and return a valid response. Any variables from the URL
        rule are passed as keyword arguments.
        """
        raise NotImplementedError()

    @classmethod
    def as_view(
        cls, name: str, *class_args: t.Any, **class_kwargs: t.Any
    ) -> ft.RouteCallable:
        """Convert the class into a view function that can be registered
        for a route.

        By default, the generated view will create a new instance of the
        view class for every request and call its
        :meth:`dispatch_request` method. If the view class sets
        :attr:`init_every_request` to ``False``, the same instance will
        be used for every request.