Mypy: Multiple inheritance from namedtuple causes error on assignment

[rbtying]

Code:

from collections import namedtuple
from typing import Dict


class A(object):
    pass


class B(A, namedtuple('bsuper', '')):
    pass

d = {}  # type: Dict[str, A]

d['hi'] = B()
d['hi2'] = A()

Error:

demo.py:14: error: Incompatible types in assignment (expression has type "B", target has type "A")

Expectation is that no error is thrown, because B inherits from A.

[gvanrossum]

Yes, we are seeing a lot of namedtuple-related bugs. :-(

[ddfisher]

This _does_ appear to be a namedtuple problem (in that it goes away when you don't inherit from namedtuple). The usage of dict isn't necessary to repro -- B doesn't appear to be regarded as a subclass of A.

[gvanrossum]

Shorter repro:

from collections import namedtuple
class A(object): pass
class B(A, namedtuple('bsuper', '')): pass
x = A()
x = B()  # E: Incompatible types in assignment (expression has type "B", variable has type "A")

[elazarg]

I believe this has been fixed. At least, the repro does not reproduce.

[gvanrossum]

Can you find the commit that fixed it using bisection?

--Guido (mobile)

[elazarg]

PR #2091, commit 590c15f

[gvanrossum]

Great! One bug down