How to find out the arity of a method in Python

Question

I\'d like to find out the arity of a method in Python (the number of parameters that it receives). Right now I\'m doing this:

def arity(obj, method):
  retur         


        

Answer 1

Ideally, you'd want to monkey-patch the arity function as a method on Python functors. Here's how:

def arity(self, method):
    return getattr(self.__class__, method).func_code.co_argcount - 1

functor = arity.__class__
functor.arity = arity
arity.__class__.arity = arity

But, CPython implements functors in C, you can't actually modify them. This may work in PyPy, though.

That's all assuming your arity() function is correct. What about variadic functions? Do you even want an answer then?