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Hi @JakubSosnovec! Thanks for bringing this question! Strict typing has been on our radar for a long time and we are correcting what is possible every time we release a new version, but this project is not 100% compatible with strict typing and we are investigating how to include it in our roadmap, but we do not have an ETA for that. I'll add this issue to our backlog and see if we can do something specifically for this case.

@heitorlessa would love to hear your thoughts here.

BTW, I'm trying here with mypy 1.4+ and Powertoos 1.25.7 and I get the same error. It seems like something is still unresolved.

❯ pip freeze
aws-lambda-powertools==1.25.7
aws-xray-sdk==2.12.1
boto3==1.34.10
botocore==1.34.10
fastjsonschema==2.19.1
jmespath==0.10.0
mypy==1.4.1
mypy-extensions==1.0.0
python-dateutil==2.8.2
s3transfer==0.10.0
six==1.16.0
tomli==2.0.1
typing-extensions==4.9.0
urllib3==1.26.18
wrapt==1.16.0

from typing import Any
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 handler(event: SQSEvent, _context: LambdaContext) -> dict[str, Any]:
    return {}

❯ mypy --strict main.py       
main.py:4: error: Untyped decorator makes function "handler" untyped  [misc]
Found 1 error in 1 file (checked 1 source file)

The simple fix for this to remove the error for event_source would be to add -> Any to def event_source, is it not? You already have the fact that the callable returns that type in the definition: handler: Callable[[Any, LambdaContext], Any],, so it is, in fact, also the correct fix.

@leandrodamascena - PR with fix submitted. Quite possibly the smallest one you'll ever see...