Modern Python Standard Library Cookbook

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functools.wraps is a very convenient tool and does its best to ensure that the decorated function looks exactly like the original one.

But while the properties of the function can easily be copied, the signature of the function itself is not as easy to copy.

So inspecting our decorated function arguments won't return the original arguments:

>>> import inspect
>>> inspect.getfullargspec(sumthree)
FullArgSpec(args=[], varargs='args', varkw='kwargs', defaults=None, 
            kwonlyargs=[], kwonlydefaults=None, annotations={})

So the reported arguments are just *args and **kwargs instead of a and b. To access the real arguments, we must dive into the underlying functions through the __wrapped__ attribute:

>>> inspect.getfullargspec(sumthree.__wrapped__) ...