Class level __getattr__ causes error: __getattr__ is not valid at the module level outside a stub file

[stoklund]

After updating to mypy 0.530, I am getting an error on a __getattr__() method defined on a class:

$ mypy --version
mypy 0.530
$ python3 --version
Python 3.6.3
[~/cretonne/lib/cretonne/meta]
$ cat mypy.ini 
[mypy]
disallow_untyped_defs = True
warn_unused_ignores = True
warn_return_any = True
[~/cretonne/lib/cretonne/meta]
$ mypy cdsl/formats.py
cdsl/formats.py:143: error: __getattr__ is not valid at the module level outside a stub file

I don't have any module level __getattr__() functions.

This didn't reproduce with a smaller test case, but you can check out the Cretonne repo to reproduce.

[emmatyping]

Confirmed on master, I am stepping through now. I appears the issue only occurs in the second pass of the checker (the class is added to the scope stack in the first pass, but not in the second).

[emmatyping]

It appears that when we defer functions to the second pass, we try to put the class context information. However, the function node is not removed on L261, so the class is not resolved, and that returns None. This later causes issues when we try to append the class context, but cannot, so the __getattr__ method appears to be in the file context (this occurs in check_second_pass). The __getattr__ checking for module levels if the first thing that relied on the size of the scope being 1 (module level), so it exposed this issue.

[gvanrossum]

Do you have a smaller repro yet?

[ilevkivskyi]

@ethanhs Your diagnosis seems right. Here is a simple repro:

class C:
    def __getattr__(self, attr: str) -> int:
        x: F
        return x.f

class F:
    def __init__(self, f: int) -> None:
        self.f = f

[ilevkivskyi]

A related bug:

from typing import TypeVar

T = TypeVar('T', bound=C)
class C:
    def m(self: T) -> T:
        class Inner:
            x: F
            f = x.f
        return self

class F:
    def __init__(self, f: int) -> None:
        self.f = f

results in a funny error:

main:5: error: The erased type of self '__main__.C' is not a supertype of its class '__main__.Inner@5'

[ilevkivskyi]

OK, here is the PR #4073.

[stoklund]

Confirmed fixed in mypy-0.540. Thanks for the quick response!