SystemError when compare with a mapping with broken length

[serhiy-storchaka]

The following code:

from multidict import MultiDict
from collections.abc import Mapping

class BadMapping(Mapping):
    def __getitem__(self, key):
        return 1
    def __iter__(self):
        yield "a"
    def __len__(self):
        1 / 0

print(MultiDict(a=1) == BadMapping())

causes raising a SystemError:

Traceback (most recent call last):
  File "<stdin>", line 7, in __len__
ZeroDivisionError: division by zero

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: <built-in method write of _io.TextIOWrapper object at 0x7f7d26f71d70> returned a result with an error set

Maybe it could even crash on debug build.