fix(event_handler): lazy load Pydantic to improve cold start (#3397)

Author: rubenfonseca

aws_lambda_powertools/event_handler/openapi/compat.py

@@ -15,9 +15,9 @@
 from pydantic import BaseModel, create_model
 from pydantic.fields import FieldInfo
 
+from aws_lambda_powertools.event_handler.openapi.pydantic_loader import PYDANTIC_V2
 from aws_lambda_powertools.event_handler.openapi.types import (
     COMPONENT_REF_PREFIX,
-    PYDANTIC_V2,
     ModelNameMap,
     UnionType,
 )

aws_lambda_powertools/event_handler/openapi/models.py

@@ -4,7 +4,7 @@
 from pydantic import AnyUrl, BaseModel, Field
 
 from aws_lambda_powertools.event_handler.openapi.compat import model_rebuild
-from aws_lambda_powertools.event_handler.openapi.types import PYDANTIC_V2
+from aws_lambda_powertools.event_handler.openapi.pydantic_loader import PYDANTIC_V2
 from aws_lambda_powertools.shared.types import Annotated, Literal
 
 """

aws_lambda_powertools/event_handler/openapi/params.py

@@ -15,7 +15,8 @@
     field_annotation_is_scalar,
     get_annotation_from_field_info,
 )
-from aws_lambda_powertools.event_handler.openapi.types import PYDANTIC_V2, CacheKey
+from aws_lambda_powertools.event_handler.openapi.pydantic_loader import PYDANTIC_V2
+from aws_lambda_powertools.event_handler.openapi.types import CacheKey
 from aws_lambda_powertools.shared.types import Annotated, Literal, get_args, get_origin
 
 """

aws_lambda_powertools/event_handler/openapi/pydantic_loader.py

@@ -0,0 +1,6 @@
+try:
+    from pydantic.version import VERSION as PYDANTIC_VERSION
+
+    PYDANTIC_V2 = PYDANTIC_VERSION.startswith("2.")
+except ImportError:
+    PYDANTIC_V2 = False

aws_lambda_powertools/event_handler/openapi/types.py

@@ -16,13 +16,6 @@
 COMPONENT_REF_TEMPLATE = "#/components/schemas/{model}"
 METHODS_WITH_BODY = {"GET", "HEAD", "POST", "PUT", "DELETE", "PATCH"}
 
-try:
-    from pydantic.version import VERSION as PYDANTIC_VERSION
-
-    PYDANTIC_V2 = PYDANTIC_VERSION.startswith("2.")
-except ImportError:
-    PYDANTIC_V2 = False
-
 
 validation_error_definition = {
     "title": "ValidationError",

tests/functional/event_handler/test_bedrock_agent.py

@@ -2,7 +2,7 @@
 from typing import Any, Dict
 
 from aws_lambda_powertools.event_handler import BedrockAgentResolver, Response, content_types
-from aws_lambda_powertools.event_handler.openapi.types import PYDANTIC_V2
+from aws_lambda_powertools.event_handler.openapi.pydantic_loader import PYDANTIC_V2
 from aws_lambda_powertools.utilities.data_classes import BedrockAgentEvent
 from tests.functional.utils import load_event