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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:
"""Alternative way to use view functions. A subclass has to implement
:meth:`dispatch_request` which is called with the view arguments from
the URL routing system. If :attr:`methods` is provided the methods
do not have to be passed to the :meth:`~flask.Flask.add_url_rule`
method explicitly::
class MyView(View):
methods = ['GET']
def dispatch_request(self, name):
return f"Hello {name}!"
app.add_url_rule('/hello/<name>', view_func=MyView.as_view('myview'))
When you want to decorate a pluggable view you will have to either do that
when the view function is created (by wrapping the return value of
:meth:`as_view`) or you can use the :attr:`decorators` attribute::
class SecretView(View):
methods = ['GET']
decorators = [superuser_required]
def dispatch_request(self):
...
The decorators stored in the decorators list are applied one after another
when the view function is created. Note that you can *not* use the class
based decorators since those would decorate the view class and not the
generated view function!
"""
#: A list of methods this view can handle.
methods: t.Optional[t.List[str]] = None
#: Setting this disables or force-enables the automatic options handling.
provide_automatic_options: t.Optional[bool] = None
#: The canonical way to decorate class-based views is to decorate the
#: return value of as_view(). However since this moves parts of the
#: logic from the class declaration to the place where it's hooked
#: into the routing system.
#:
#: You can place one or more decorators in this list and whenever the
#: view function is created the result is automatically decorated.
#:
#: .. versionadded:: 0.8
decorators: t.List[t.Callable] = []
def dispatch_request(self) -> ft.ResponseReturnValue:
"""Subclasses have to override this method to implement the
actual view function code. This method is called with all
the arguments from the URL rule.
"""
raise NotImplementedError()
@classmethod
def as_view(
cls, name: str, *class_args: t.Any, **class_kwargs: t.Any
) -> t.Callable:
"""Converts the class into an actual view function that can be used
with the routing system. Internally this generates a function on the
fly which will instantiate the :class:`View` on each request and call
the :meth:`dispatch_request` method on it.
The arguments passed to :meth:`as_view` are forwarded to the
constructor of the class.
"""
def view(*args: t.Any, **kwargs: t.Any) -> ft.ResponseReturnValue:
self = view.view_class(*class_args, **class_kwargs) # type: ignore
return current_app.ensure_sync(self.dispatch_request)(*args, **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 MethodViewType(type):
"""Metaclass for :class:`MethodView` that determines what methods the view
defines.
"""
def __init__(cls, name, bases, d):
super().__init__(name, bases, d)
if "methods" not in d:
methods = set()
for base in bases:
if getattr(base, "methods", None):
methods.update(base.methods)
for key in http_method_funcs:
if hasattr(cls, key):
methods.add(key.upper())
# If we have no method at all in there we don't want to add a
# method list. This is for instance the case for the base class
# or another subclass of a base method view that does not introduce
# new methods.
if methods:
cls.methods = methods
class MethodView(View, metaclass=MethodViewType):
"""A class-based view that dispatches request methods to the corresponding
class methods. For example, if you implement a ``get`` method, it will be
used to handle ``GET`` requests. ::
class CounterAPI(MethodView):
def get(self):
return session.get('counter', 0)
def post(self):
session['counter'] = session.get('counter', 0) + 1
return 'OK'
app.add_url_rule('/counter', view_func=CounterAPI.as_view('counter'))
"""
def dispatch_request(self, *args: t.Any, **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)(*args, **kwargs)
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