Wrong type inference for `<tuple>[s]` where `s: slice`
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bug
- Dominant language
- Python
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Description
Bug Report
a = (1, 2, 3)
s = slice(None, 1)
reveal_type(a[s]) # Revealed type is `builtins.int`
reveal_type(a.__getitem__(s)) # Revealed type is `builtins.tuple[builtins.int, ...]` (OK)
The runtime value of a[s] is (1,).
The type inference works for lists though.
Your Environment
- Mypy version used: 1.0.0-2.1, master
- Python version used: 3.12, 3.13
Contributor guide
First steps
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- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the supplied tuple and slice reproducer, then trace mypy's tuple subscription type inference and compare it with the existing list-slice handling. Done means both a[s] and a.__getitem__(s) reveal a tuple type consistent with the runtime value, without regressing ordinary tuple indexing.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 68/100