python / python/mypy

(🐞) Invalid `valid-type` error when using a variable as a value, not as a type

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#14,583 2 comments 3 reactions 0 assignees View on GitHub

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bug
Dominant language
Python
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Description

a: type[object]
b: type[object] = list[a]   #  Variable "__main__.a" is not valid as a type  [valid-type]

Here I am not using a as a 'type' (TypeAlias or annotation), I'm using it as a value, so this error seems like it shouldn't apply.

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Research direction

Start by reproducing the reported snippet with mypy and tracing the valid-type diagnostic for a variable used as a value. Compare that behavior with uses where the variable is genuinely treated as a type; done means the value use no longer reports this error while invalid type uses still do.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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