perf: avoid importing Pydantic v1 for v2 handlers

src/azure_functions_validation/decorator.py

@@ -4,12 +4,12 @@
 
 from collections.abc import Callable, Mapping
 import inspect
+import sys
 import types
 from typing import Any, get_type_hints
 import warnings
 
 from pydantic import TypeAdapter
-from pydantic.v1 import BaseModel as BaseModelV1
 
 from ._endpoint import build_endpoint_metadata, set_endpoint_metadata
 from ._metadata import METADATA_ATTR, ValidationMetadata, set_validation_metadata
@@ -146,7 +146,13 @@ def decorator(func: Callable[..., Any]) -> Callable[..., Any]:
             ("request_model", request_model),
             ("response_model", response_model),
         ):
-            if isinstance(model, type(BaseModelV1)) and issubclass(model, BaseModelV1):
+            legacy_module = sys.modules.get("pydantic.v1")
+            legacy_base = getattr(legacy_module, "BaseModel", None)
+            if (
+                legacy_base is not None
+                and isinstance(model, type)
+                and issubclass(model, legacy_base)
+            ):
                 raise TypeError(
                     f"{option_name} uses a Pydantic v1 model; Pydantic v2 models are required"
                 )

tests/test_lazy_legacy_import.py

@@ -0,0 +1,20 @@
+import subprocess
+import sys
+
+
+def test_v2_decoration_does_not_import_legacy_pydantic() -> None:
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            "import sys; from pydantic import BaseModel; "
+            "from azure_functions_validation import validate_http; "
+            "Model = type('Model', (BaseModel,), {'__annotations__': {'name': str}}); "
+            "validate_http(body=Model)(lambda req, body: body); "
+            "assert 'pydantic.v1' not in sys.modules",
+        ],
+        capture_output=True,
+        text=True,
+        timeout=30,
+    )
+    assert result.returncode == 0, result.stderr