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Static typing: event_source makes handler untyped under mypy --strict #8331
Description
Static type checker used
mypy (project's standard)
AWS Lambda function runtime
3.14
Powertools for AWS Lambda (Python) version
3.31.0
Static type checker info
mypy 2.1.0 & mypy_extensions==1.1.0
Code snippet
"""Example handler."""
from aws_lambda_powertools.utilities.data_classes import SQSEvent, event_source
from aws_lambda_powertools.utilities.typing import LambdaContext
@event_source(data_class=SQSEvent)
def lambda_handler(event: SQSEvent, _context: LambdaContext) -> None:
"""..."""Possible Solution
Re-opening of #3568 with new approach for solving this.
#### Diagnosis
event_source defines return types as Any, rather than using a type variable, plus lambda_handler_decorator's return type is simply Callable (equivalent to Callable[..., Any]) that mypy gets for the usage of the wrapper.
It's quite hard annotating lambda_handler_decorator accurately for all uses cases of it, but the specific one in event_source.py is simpler.
Proposed solution
Define the resultant type of lambda_handler_decorator(_event_source) as decorated, since this has data_class as keyword only I think this is only possible with a Protocol. We then cannot annotate the wrapped function directly so just cast afterwards.
Activity
boring-cyborg commentedon Jul 11, 2026
Thanks for opening your first issue here! We'll come back to you as soon as we can.
In the meantime, check out the #python channel on our Powertools for AWS Lambda Discord: Invite link
leandrodamascena commentedon Jul 12, 2026
Hey @stenczelt thanks a lot for opening this. I just saw the PR and looks good to merge.
powertools-for-aws-oss-automation commentedon Jul 12, 2026
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github-actions commentedon Jul 13, 2026
This is now released under 3.31.1 version!