Get actual call signature?

[Jarek Zgoda]

Say, I have a function defined as:

def fun(arg_one, arg_two='x', arg_three=None):
    pass

Is there any way to get actual arguments that will be effectively used
when I call this function in various ways, like:

fun(5) => [5, 'x', None]
fun(5, arg_three=['a', 'b']) => [5, 'x', ['a', 'b']]
fun(5, 'something') => [5, 'something', None]

(et caetera, using all possible mixes of positional, keyword and default
arguments)

I'd like to wrap function definition with a decorator that intercepts
not only passed arguments, but also defaults that will be actually used
in execution.

If this sounds not feasible (or is simply impossible), I'll happily
throw this idea and look for another one. ;)

-- 
Jarek Zgoda
Skype: jzgoda | GTalk: zgoda at jabber.aster.pl | voice: +48228430101

"We read Knuth so you don't have to." (Tim Peters)