Difference in behaviour between overload and TypeVars when using functools.update_wrapper
Nobody has claimed this yet.
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Bug Report
When calling functools.update_wrapper(f, g) where f has a type of TypeVar('T', Type1, Type2), mypy errors incorrectly, saying it expects Callable[[Never], Never] in that spot.
To Reproduce
https://mypy-play.net/?mypy=latest&python=3.12&gist=8b79db2fe7eb042e15122536a393dd43
Expected Behavior
I think f1 and f2 are identical functions. I expect both checks to succeed (as they did on mypy 1.9.0), or possibly both to fail (but if this is an error, I don't see why...).
Actual Behavior
update_wrapper(f1, g) succeeds and update_wrapper(f2, g) errors, with the message Argument 1 to "update_wrapper" has incompatible type "Callable[[T], T]"; expected "Callable[[Never], Never]" [arg-type]
Your Environment
- Mypy version used: 1.9.0 -> 1.10.0
- Python version used: 3.10, 3.12
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the linked mypy-play reproduction and compare the overload and TypeVar cases around functools.update_wrapper across mypy 1.9.0 and 1.10.0. Trace the callable typing behavior that produces the reported Never expectation; done means the two equivalent checks have a consistent, intended result when the reproduction is rerun.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100