feat(parser): infer model from type hint

aws_lambda_powertools/utilities/parser/parser.py

@@ -1,4 +1,5 @@
 import logging
+import typing
 from typing import Any, Callable, Dict, Optional, Type, overload
 
 from aws_lambda_powertools.utilities.parser.compat import disable_pydantic_v2_warning
@@ -17,7 +18,7 @@ def event_parser(
     handler: Callable[[Any, LambdaContext], EventParserReturnType],
     event: Dict[str, Any],
     context: LambdaContext,
-    model: Type[Model],
+    model: Type[Model] = None,
     envelope: Optional[Type[Envelope]] = None,
 ) -> EventParserReturnType:
     """Lambda handler decorator to parse & validate events using Pydantic models
@@ -76,11 +77,20 @@ def handler(event: Order, context: LambdaContext):
     ValidationError
         When input event does not conform with model provided
     InvalidModelTypeError
-        When model given does not implement BaseModel
+        When model given does not implement BaseModel or is not provided
     InvalidEnvelopeError
         When envelope given does not implement BaseEnvelope
     """
-    parsed_event = parse(event=event, model=model, envelope=envelope) if envelope else parse(event=event, model=model)
+    if model is None:
+        type_hints = typing.get_type_hints(handler)
+        model = type_hints.get("event")
+        if model is None:
+            raise InvalidModelTypeError(
+                "The model must be provided either as the `model` argument to `event_parser`"
+                "or as the type hint of `event` in the handler that it wraps",
+            )
+
+    parsed_event = parse(event=event, model=model, envelope=envelope)
     logger.debug(f"Calling handler {handler.__name__}")
     return handler(parsed_event, context)
 

tests/functional/parser/test_parser.py

@@ -93,3 +93,20 @@ def handle_no_envelope(event: Union[Dict, str], _: LambdaContext):
         return event
 
     handle_no_envelope(dummy_event, LambdaContext())
+
+
+def test_parser_event_with_type_hint(dummy_event, dummy_schema):
+    @event_parser()
+    def handler(event: dummy_schema, _: LambdaContext):
+        assert event.message == "hello world"
+
+    handler(dummy_event["payload"], LambdaContext())
+
+
+def test_parser_event_without_type_hint(dummy_event, dummy_schema):
+    @event_parser()
+    def handler(event, _):
+        assert event.message == "hello world"
+
+    with pytest.raises(exceptions.InvalidModelTypeError):
+        handler(dummy_event["payload"], LambdaContext())