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

https://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references:

Any identifier of the form _spam (at least two leading underscores, at most one trailing underscore) is textually replaced with classname__spam, where classname is the current class name with leading underscore(s) stripped. This mangling is done without regard to the syntactic position of the identifier, as long as it occurs within the definition of a class.

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