How to get segmentation fault with crazy __ (python 2 and 3)

underscore_bug.py

__obj = object()
# uncomment for fix:
# _Class__obj = __obj


def func():
    print('func:', __obj)


class Class:

    def class_func(self):
        # uncomment for get !!SEGMENTATION FAULT!!:
        # nonlocal __obj
        print('class_func:',  __obj)

print('---')
func()
# OK:
# -> func: <object object at 0x7f515eccf070>

print('---')
c = Class()
c.class_func()
# WTF??>:
# -> NameError: name '_Class__obj' is not defined

Segmentation fault report - https://bugs.python.org/issue25973