PEP 742 (TypeIs) tracker #11453
Description
This issue is supposed to track when we can start to use the TypeIs special form (PEP 742) in typeshed. Support is needed in released versions of:
- PEP accepted
- mypy (Implement TypeIs (PEP 742) mypy#16898)
- pytype (Support PEP 742 (TypeIs) google/pytype#1588)
- pyright (Implement support for TypeIs (PEP 742) microsoft/pyright#7293)
- pyre (optional)
- PyCharm (optional)
Please reference this issue as needed from other issues/PRs to collect places that we might want to update.
Once this is supported, many (most?) TypeGuard functions in typeshed should be changed to use TypeIs.
Activity
sterliakov commented on Apr 27, 2024
Following #11823, should all also become a TypeIs guard against None elements?
This wasn't possible with TypeGuard due to undesired type narrowing (iterable type would be lost, Sequence[int | None] would become Iterable[int]), but with TypeIs intersection semantics that problem should not arise (Sequence[int| None] & Iterable[int] should be reducible to Sequence[int], if I'm not mistaken, which is the desirable outcome).
JelleZijlstra commented on Apr 27, 2024
Intuitively that seems fine but both mypy and pyright have some issues with this (e.g., they seem to reduce list[str | None] & Iterable[str] to Never): https://pyright-play.net/?pyrightVersion=1.1.359&pythonVersion=3.13&code=GYJw9gtgBALgngBwJYDsDmUkQWEMogCmAboQIYA2A%2BvAoQDRQCSMhIZARhYQLABQoSLESo0VQgA9WKAM5IwszNlz4AKokJMZ-fgBNCwKJQoBtKqoC6ACiSt2XQgC5mdztzOqoAHygA5BYQWjAD0AJRQALQAfFDqdFomLGxuhB4WFs4AdNk6fPqGMmTY3FYSzkn27jIwIN5%2BAUFQcM4USNUm1bU%2B-iiBoY78UEOYhsal-YPDU0SklDQa45NDhBQyTktTBCTk1LSEi3xTSKMUFFZwE4ebQzM783TnoRsrawNX17dze49AA, https://mypy-play.net/?mypy=latest&python=3.12&gist=b4a3be40d6e245ac7e65ff9ffac03355
Worth trying with an exploratory PR, and maybe with tweaks to the intersection logic in mypy and/or pyright.
Anyway, I'm closing this PR as we can use TypeIs in typeshed now. Feel free to open specific issues about places where TypeIs could be used.