"Functions that help with dynamically creating decorators for views."
from functools import 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
[docs]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
[docs]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)
[docs]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)()
def make_middleware_decorator(middleware_class):
def _make_decorator(*m_args, **m_kwargs):
def _decorator(view_func):
middleware = middleware_class(view_func, *m_args, **m_kwargs)
@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
[docs]def sync_and_async_middleware(func):
"""
Mark a middleware factory as returning a hybrid middleware supporting both
types of request.
"""
func.sync_capable = True
func.async_capable = True
return func
[docs]def sync_only_middleware(func):
"""
Mark a middleware factory as returning a sync middleware.
This is the default.
"""
func.sync_capable = True
func.async_capable = False
return func
[docs]def async_only_middleware(func):
"""Mark a middleware factory as returning an async middleware."""
func.sync_capable = False
func.async_capable = True
return func
Jul 28, 2023