Bug: Using @metrics.log_metrics and @event_parser on the same handler causes a type error.

[brdskggs]

Expected Behaviour

I expect to be able to use @metrics.log_metrics and @event_parser on the same Lambda handler. It doesn't work, regardless of order they are used to annotate the handler.

Current Behaviour

I get the following error in VS Code, according to Pylance:

Argument of type "(event: AgentQuery, context: LambdaContext) -> str" cannot be assigned to parameter "lambda_handler" of type "((Dict[Unknown, Unknown], Any) -> Any) | ((Dict[Unknown, Unknown], Any, Dict[Unknown, Unknown] | None) -> Any) | None" in function "__call__"
  Type "(event: AgentQuery, context: LambdaContext) -> str" cannot be assigned to type "((Dict[Unknown, Unknown], Any) -> Any) | ((Dict[Unknown, Unknown], Any, Dict[Unknown, Unknown] | None) -> Any) | None"
    Type "(event: AgentQuery, context: LambdaContext) -> str" cannot be assigned to type "(Dict[Unknown, Unknown], Any) -> Any"
      Parameter 1: type "Dict[Unknown, Unknown]" cannot be assigned to type "AgentQuery"
        "Dict[Unknown, Unknown]" is incompatible with "AgentQuery"
    Type "(event: AgentQuery, context: LambdaContext) -> str" cannot be assigned to type "(Dict[Unknown, Unknown], Any, Dict[Unknown, Unknown] | None) -> Any"
      Function accepts too many positional parameters; expected 2 but received 3
        Parameter 1: type "Dict[Unknown, Unknown]" cannot be assigned to type "AgentQuery"
          "Dict[Unknown, Unknown]" is incompatible with "AgentQuery"
Argument missing for parameter "context"

Code snippet

import json
from typing import List

from aws_lambda_powertools import Logger, Metrics
from aws_lambda_powertools.utilities.parser import BaseModel, Field, event_parser
from aws_lambda_powertools.utilities.typing import LambdaContext


logger = Logger()
metrics = Metrics()


class AgentQuery(BaseModel):
    username: str
    user_query: str


@logger.inject_lambda_context
@metrics.log_metrics(capture_cold_start_metric=True)
@event_parser(model=AgentQuery)
def lambda_handler(event: AgentQuery, context: LambdaContext):
    logger.info("hi")

### Possible Solution

Parser and Event Sources mutate the event, but `log_metrics` expect a dict.

Potential fix is to update type annotations for handler passed to `log_metrics` to be `AnyCallableT`.

### Steps to Reproduce

Paste the code in VS Code, and look at the Problems tab highlighted by Pylance.

### Powertools for AWS Lambda (Python) version

latest

### AWS Lambda function runtime

3.9

### Packaging format used

PyPi

### Debugging logs

_No response_

[boring-cyborg]

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

[heitorlessa]

looking into it now.

[heitorlessa]

PR is up with the fix. That said, Pylance complains about typing being partially unknown. While I'd love to find a solution for it, mypy (our preferred static checker) is happy with it. I suspect is due to now using ParamSpec but that doesn't work well with partial to support decorators with @metrics.log_metrics, @metrics.log_metrics(), @metrics.log_metrics(params...).

We should maybe do a campaign next year to identify what Pylance issues are worth resolving.

[github-actions]

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[github-actions]

This is now released under 2.29.0 version!