Source code for flask.views
import typing as t
from . import typing as ft
from .globals import current_app
from .globals import request
http_method_funcs = frozenset(
["get", "post", "head", "options", "delete", "put", "trace", "patch"]
)
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.Optional[t.Collection[str]]] = 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[t.Optional[bool]] = 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[t.List[t.Callable]] = []
#: 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.
Except for ``name``, all other arguments passed to this method
are forwarded to the view class ``__init__`` method.
.. versionchanged:: 2.2
Added the ``init_every_request`` class attribute.
"""
if cls.init_every_request:
def view(**kwargs: t.Any) -> ft.ResponseReturnValue:
self = view.view_class( # type: ignore[attr-defined]
*class_args, **class_kwargs
)
return current_app.ensure_sync(self.dispatch_request)(**kwargs)
else:
self = cls(*class_args, **class_kwargs)
def view(**kwargs: t.Any) -> ft.ResponseReturnValue:
return current_app.ensure_sync(self.dispatch_request)(**kwargs)
if cls.decorators:
view.__name__ = name
view.__module__ = cls.__module__
for decorator in cls.decorators:
view = decorator(view)
# We attach the view class to the view function for two reasons:
# first of all it allows us to easily figure out what class-based
# view this thing came from, secondly it's also used for instantiating
# the view class so you can actually replace it with something else
# for testing purposes and debugging.
view.view_class = cls # type: ignore
view.__name__ = name
view.__doc__ = cls.__doc__
view.__module__ = cls.__module__
view.methods = cls.methods # type: ignore
view.provide_automatic_options = cls.provide_automatic_options # type: ignore
return view
class MethodView(View):
"""Dispatches request methods to the corresponding instance methods.
For example, if you implement a ``get`` method, it will be used to
handle ``GET`` requests.
This can be useful for defining a REST API.
:attr:`methods` is automatically set based on the methods defined on
the class.
See :doc:`views` for a detailed guide.
.. code-block:: python
class CounterAPI(MethodView):
def get(self):
return str(session.get("counter", 0))
def post(self):
session["counter"] = session.get("counter", 0) + 1
return redirect(url_for("counter"))
app.add_url_rule(
"/counter", view_func=CounterAPI.as_view("counter")
)
"""
def __init_subclass__(cls, **kwargs: t.Any) -> None:
super().__init_subclass__(**kwargs)
if "methods" not in cls.__dict__:
methods = set()
for base in cls.__bases__:
if getattr(base, "methods", None):
methods.update(base.methods) # type: ignore[attr-defined]
for key in http_method_funcs:
if hasattr(cls, key):
methods.add(key.upper())
if methods:
cls.methods = methods
def dispatch_request(self, **kwargs: t.Any) -> ft.ResponseReturnValue:
meth = getattr(self, request.method.lower(), None)
# If the request method is HEAD and we don't have a handler for it
# retry with GET.
if meth is None and request.method == "HEAD":
meth = getattr(self, "get", None)
assert meth is not None, f"Unimplemented method {request.method!r}"
return current_app.ensure_sync(meth)(**kwargs)
