Cannot infer type of lambda regression with mypy 1.9
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Description
Bug Report
The lambda in the following code snippet reports error: Cannot infer type of lambda starting from mypy 1.9.0 (It did not report an error with mypy 1.8.0).
https://github.com/python/mypy/issues/15459 seems related, but it looks as mypy 1.8.0 also reported an error there.
To Reproduce
import asyncio
import signal
async def shutdown(
signal: signal.Signals,
) -> None:
print(signal.name)
async def main() -> None:
loop = asyncio.get_event_loop()
signals = (signal.SIGHUP, signal.SIGTERM, signal.SIGINT)
for s in signals:
loop.add_signal_handler(
s,
lambda s=s: asyncio.create_task( # <-- error: Cannot infer type of lambda [misc]
shutdown(
signal=s,
),
name="shutdown",
),
)
Expected Behavior
No error shown regarding the lambda.
Actual Behavior
mypy reports Cannot infer type of lambda [misc]
Your Environment
- Mypy version used: 1.9.0
- Mypy command-line flags: --strict
- Mypy configuration options from
mypy.ini(and other config files): - - Python version used: 3.11.8
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 by running the supplied reproducer with mypy 1.8.0 and 1.9.0 using --strict, then compare the behavior in the linked mypy playground. Investigate the lambda type-inference regression shown in the example; done means the current version no longer reports Cannot infer type of lambda for this code.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100