Cannot use nested class in type context via self

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
38/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start by reproducing the nested Foo.Bar example in test.py with mypy and compare the reported assignment error. Trace the relevant type-context handling, then add coverage showing that a supported annotation lets self._bar receive Foo.Bar without an incompatible-types error.

Written by the indexing model from the issue text.

Description

feature priority-2-low

I cannot get the following program to type check:

from typing import *

class Foo:
    class Bar:
        pass

    def __init__(self) -> None:
        self._bar = None

    def start(self) -> None:
        self._bar = self.Bar()

I get the following error:

test.py:11: error: Incompatible types in assignment (expression has type "Bar", variable has type "None")

Trying to add types like:

self._bar = None  # type: Bar

Or:

self._bar = None  # type: self.Bar

Does not work.

Dominant language
Python
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Avg merge
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Merged PRs (30d)
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