# Django 2.2.9.dev20191202104323 文档

# django.utils.decorators 源代码

    "Functions that help with dynamically creating decorators for views."

    # For backwards compatibility in Django 2.0.
    from contextlib import ContextDecorator  # noqa
    from functools import WRAPPER_ASSIGNMENTS, partial, update_wrapper, wraps

    class classonlymethod(classmethod):
        def __get__(self, instance, cls=None):
            if instance is not None:
                raise AttributeError("This method is available only on the class, not on instances.")
            return super().__get__(instance, cls)

    def _update_method_wrapper(_wrapper, decorator):
        # _multi_decorate()'s bound_method isn't available in this scope. Cheat by
        # using it on a dummy function.
        @decorator
        def dummy(*args, **kwargs):
            pass
        update_wrapper(_wrapper, dummy)

    def _multi_decorate(decorators, method):
        """
        Decorate `method` with one or more function decorators. `decorators` can be
        a single decorator or an iterable of decorators.
        """
        if hasattr(decorators, '__iter__'):
            # Apply a list/tuple of decorators if 'decorators' is one. Decorator
            # functions are applied so that the call order is the same as the
            # order in which they appear in the iterable.
            decorators = decorators[::-1]
        else:
            decorators = [decorators]

        def _wrapper(self, *args, **kwargs):
            # bound_method has the signature that 'decorator' expects i.e. no
            # 'self' argument, but it's a closure over self so it can call
            # 'func'. Also, wrap method.__get__() in a function because new
            # attributes can't be set on bound method objects, only on functions.
            bound_method = partial(method.__get__(self, type(self)))
            for dec in decorators:
                bound_method = dec(bound_method)
            return bound_method(*args, **kwargs)

        # Copy any attributes that a decorator adds to the function it decorates.
        for dec in decorators:
            _update_method_wrapper(_wrapper, dec)
        # Preserve any existing attributes of 'method', including the name.
        update_wrapper(_wrapper, method)
        return _wrapper

    def method_decorator(decorator, name=''):
        """
        Convert a function decorator into a method decorator
        """
        # 'obj' can be a class or a function. If 'obj' is a function at the time it
        # is passed to _dec,  it will eventually be a method of the class it is
        # defined on. If 'obj' is a class, the 'name' is required to be the name
        # of the method that will be decorated.
        def _dec(obj):
            if not isinstance(obj, type):
                return _multi_decorate(decorator, obj)
            if not (name and hasattr(obj, name)):
                raise ValueError(
                    "The keyword argument `name` must be the name of a method "
                    "of the decorated class: %s. Got '%s' instead." % (obj, name)
                )
            method = getattr(obj, name)
            if not callable(method):
                raise TypeError(
                    "Cannot decorate '%s' as it isn't a callable attribute of "
                    "%s (%s)." % (name, obj, method)
                )
            _wrapper = _multi_decorate(decorator, method)
            setattr(obj, name, _wrapper)
            return obj

        # Don't worry about making _dec look similar to a list/tuple as it's rather
        # meaningless.
        if not hasattr(decorator, '__iter__'):
            update_wrapper(_dec, decorator)
        # Change the name to aid debugging.
        obj = decorator if hasattr(decorator, '__name__') else decorator.__class__
        _dec.__name__ = 'method_decorator(%s)' % obj.__name__
        return _dec

    def decorator_from_middleware_with_args(middleware_class):
        """
        Like decorator_from_middleware, but return a function
        that accepts the arguments to be passed to the middleware_class.
        Use like::

             cache_page = decorator_from_middleware_with_args(CacheMiddleware)
             # ...

             @cache_page(3600)
             def my_view(request):
                 # ...
        """
        return make_middleware_decorator(middleware_class)

    def decorator_from_middleware(middleware_class):
        """
        Given a middleware class (not an instance), return a view decorator. This
        lets you use middleware functionality on a per-view basis. The middleware
        is created with no params passed.
        """
        return make_middleware_decorator(middleware_class)()

    # Unused, for backwards compatibility in Django 2.0.
    def available_attrs(fn):
        """
        Return the list of functools-wrappable attributes on a callable.
        This was required as a workaround for https://bugs.python.org/issue3445
        under Python 2.
        """
        return WRAPPER_ASSIGNMENTS

    def make_middleware_decorator(middleware_class):
        def _make_decorator(*m_args, **m_kwargs):
            middleware = middleware_class(*m_args, **m_kwargs)

            def _decorator(view_func):
                @wraps(view_func)
                def _wrapped_view(request, *args, **kwargs):
                    if hasattr(middleware, 'process_request'):
                        result = middleware.process_request(request)
                        if result is not None:
                            return result
                    if hasattr(middleware, 'process_view'):
                        result = middleware.process_view(request, view_func, args, kwargs)
                        if result is not None:
                            return result
                    try:
                        response = view_func(request, *args, **kwargs)
                    except Exception as e:
                        if hasattr(middleware, 'process_exception'):
                            result = middleware.process_exception(request, e)
                            if result is not None:
                                return result
                        raise
                    if hasattr(response, 'render') and callable(response.render):
                        if hasattr(middleware, 'process_template_response'):
                            response = middleware.process_template_response(request, response)
                        # Defer running of process_response until after the template
                        # has been rendered:
                        if hasattr(middleware, 'process_response'):
                            def callback(response):
                                return middleware.process_response(request, response)
                            response.add_post_render_callback(callback)
                    else:
                        if hasattr(middleware, 'process_response'):
                            return middleware.process_response(request, response)
                    return response
                return _wrapped_view
            return _decorator
        return _make_decorator

    class classproperty:
        def __init__(self, method=None):
            self.fget = method

        def __get__(self, instance, cls=None):
            return self.fget(cls)

        def getter(self, method):
            self.fget = method
            return self