Change idlelib.CallTips.get_argspec to use inspect.signature, new in 3.3, instead of inspect.getfullargspec and inspect.formatargspec. One thing it handles better is a namedtuple class, which has a C-coded __init__ inherited from object a Python-coded __new__ written by namedtuple. Signature() will also handle C-coded functions if and when Argument Clinic (new in 3.4) adds signature information. from collections import namedtuple from inspect import signature Point = namedtuple('Point', 'x y') print(signature(Point.__new__)) # '(_cls, x, y)' print(signature(Point)) # '(x, y)' Note that str (called by print) is needed to get the desired string form. There are tests in CallTips.py, but they should be converted to unittest, moved to idle_test/test_calltips.py, changed to match new output detail, and expanded to include new examples.