python / python/mypy

(🐞) No error when empty tuple used as type parameter

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#12,316 1 comment 1 reaction 0 assignees View on GitHub

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bug priority-2-low
Dominant language
Python
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Description

l: list[()][int]

No mypy error but this fails at runtime.

I have no idea what this supposed to do, empty tuple as an argument is only mentioned in the pep for tuple

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Research direction

Start by reproducing the provided list[()][int] snippet and confirm that mypy accepts it while runtime evaluation fails. Trace the type-parameter handling for empty tuples, then add a regression test showing that this construct produces an appropriate mypy error.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
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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