mypy can't tell a "private" private attribute defined in a sub-class as being different from a same-named "private" private attribute defined in the base class.

[asincero]

Steps to reproduce

mypy thinks the attribute defined on line 10 refers to the attribute defined on line 5:

import typing

class Base:
    def __init__(self) -> None:
        self.__private_attr: typing.Optional[int] = 69
        
class Derived(Base):
    def __init__(self) -> None:
        super().__init__()
        self.__private_attr = ''

Current behavior

mypy reports the following error:

t1.py:10: error: Incompatible types in assignment (expression has type "str", variable has type "Optional[int]")

Expected behavior

mypy shouldn't report anything.

mypy --version output

mypy 0.670

[ilevkivskyi]

Duplicate of #523

This shouldn't be too hard to fix, PRs are welcome.