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Date: Thu, 08 Dec 2011 15:34:13 -0800
From: Ethan Furman <ethan@stoneleaf.us>
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To: python-list@python.org
Subject: Re: I love the decorator in Python!!!
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:16885

Chris Angelico wrote:
> One piece of sophistication that I would rather like to see, but don't
> know how to do. Instead of *args,**kwargs, is it possible to somehow
> copy in the function's actual signature? I was testing this out in
> IDLE, and the fly help for the function no longer gave useful info
> about its argument list.

If you want to roll your own, it looks something like this:

2.x code
----------------------------------------------------------------------
def trace(func, debugmode=debugmode):
     if debugmode:
         name = func.__name__
         argspec = inspect.getargspec(func)
         signature = inspect.formatargspec(
             formatvalue=lambda val: "", *argspec)[1:-1] # trim parens
         new_func = (
                     'def _wrapper_(%(signature)s):\n'
                     '    print(">"+func.__name__)\n'
                     '    result = func(%(signature)s)\n'
                     '    print("<"+func.__name__)\n'
                     '    return result\n'
                     % {'signature':signature}
                     )
         evaldict = {'func':func}
         exec new_func in evaldict
         wrapped = evaldict['_wrapper_']
         wrapped.__name__ = name
         wrapped.__doc__ = func.__doc__
         wrapped.__module__ = func.__module__
         wrapped.__dict__ = func.__dict__
         wrapped.func_defaults = func.func_defaults
         return wrapped
     return func
----------------------------------------------------------------------

The downside (which you get even with Michele's decorator module) is 
that tracebacks aren't quite as clean.

~Ethan~