Rust Python gets crashing when rebinding __repr__ as __str__ #2778

Rust Python interpreter crashes when rebinding repr as str.

class Foo(object):
    pass

Foo.__repr__ = Foo.__str__

foo = Foo()
str(foo)

Actual output:

Segmentation fault (core dumped)

System:

Ubuntu 16.04
Rust Python 0.1.2 interpreter