The following code causes a segmentation fault:
class Failure(object):
    def __getattr__(self, attr):
        return (self, None)
issubclass(Failure(), int)

I am running a macbook pro, OS X 10.12.4, and have observed the problem in python 3.5.2, 3.6.0, and 3.6.1.

It appears that returning (self,) causes it to go into an infinite loop attempting to get `x.__bases__`, and returning `(self, y)` for any value `y` causes it to attempt to get `x.__bases__` 262,030 times and then segfault.

A crash log is attached.