Knowing the signature of a function

[Xavier Décoret]

Hello,

I have the following code:

def foo(x,y):
	pass

How can I query the function object foo to know the number of parameters 
it expects.  I can find it is a function using callable(f), I can find 
some information (listed by dir(foo)) such as the name of the 
function,etc.. but nowhere I can find the number of arguments.

I would like to know wether the function expects one or zero arguments.