Maintaining signature in help(decorated function)

[jelsas]

Hi -- I can't seem to maintain the function signature when applying a
decorator.  I'm using functools.wraps.  Example:

>>> def mydecorator(fn):
...     from functools import wraps
...     # simple decorator
...     @wraps(fn)
...     def wrapped(*args, **kwargs):
...             print 'i\'m wrapped!'
...             return fn(*args, **kwargs)
...     return wrapped
...
>>>
>>> @mydecorator
... def f(foo, bar):
...     '''docstring for f'''
...     pass
...
>>>
>>> help(f)

displays:

Help on function f in module __main__:

f(*args, **kwargs)
    docstring for f

I would like to maintain f's signature in the help message, (foo, bar)
instead of (*args, **kwargs)

Thanks in advance!