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

here is another attempt using metaclass, as i use python 2.5, but with 2.6 you could easily decorate the class

metaclass can also be defined at module level, so it works for all classes

from types import FunctionType

def arity(unboundmethod):
    def _arity():
        return unboundmethod.func_code.co_argcount - 1 # remove self
    unboundmethod.arity = _arity

    return unboundmethod

class AirtyMetaclass(type):
    def __new__(meta, name, bases, attrs):
        newAttrs = {}
        for attributeName, attribute in attrs.items():
            if type(attribute) == FunctionType:
                attribute = arity(attribute)

            newAttrs[attributeName] = attribute

        klass = type.__new__(meta, name, bases, newAttrs)

        return klass

class Foo:
    __metaclass__ = AirtyMetaclass
    def bar(self, bla):
        pass

print Foo().bar.arity()