>>> def decorator(func):
...     def wrapper(arg):
...        return func(arg)
...     wrapper.__name__ = func.__name__
...     wrapper.__dict__.update(func.__dict__)
...     return wrapper
...
>>> @decorator
... def foo(arg):
...     print arg
...     return arg
...
>>> foo(1)
1
1
>>> foo(1, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: wrapper() takes exactly 1 argument (2 given)
>>> foo.__name__
'foo'
>>>