Support adding class variables to class through assignment

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#8,723 5 comments 19 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
30/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start by tracing how mypy handles assignments to self in setUp and class-variable declarations, then inspect tests covering ClassVar and unittest setup hooks. Define expected diagnostics for cls.foo and self.foo in setUpClass or setUpTestData, and add focused regression tests showing that the supported assignments no longer produce attribute errors.

Written by the indexing model from the issue text.

Description

feature priority-2-low

Mypy supports adding items to self during test setUp, which is great. However in many cases it's useful to be able to add items to the class during setUpClass (or Django's setUpTestData).

import unittest

class Tests(unittest.TestCase):
    @classmethod
    def setUpClass(cls) -> None:
        cls.foo = 42  # "Type[Tests]" has no attribute "foo"

    def test_foo(self) -> None:
        print(self.foo)  # "Tests" has no attribute "foo"

Adding a ClassVar allows for a workaround to this, however it would be nice if that wasn't needed.

Dominant language
Python
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Merged PRs (30d)
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