♻️ Handle Pydantic v1 imports for checks conditionally, filtering warnings

fastapi/_compat/__init__.py

@@ -31,6 +31,8 @@ from .shared import PYDANTIC_V2 as PYDANTIC_V2
 from .shared import PYDANTIC_VERSION_MINOR_TUPLE as PYDANTIC_VERSION_MINOR_TUPLE
 from .shared import annotation_is_pydantic_v1 as annotation_is_pydantic_v1
 from .shared import field_annotation_is_scalar as field_annotation_is_scalar
+from .shared import is_pydantic_v1_model_class as is_pydantic_v1_model_class
+from .shared import is_pydantic_v1_model_instance as is_pydantic_v1_model_instance
 from .shared import (
     is_uploadfile_or_nonable_uploadfile_annotation as is_uploadfile_or_nonable_uploadfile_annotation,
 )

fastapi/_compat/may_v1.py

@@ -1,9 +1,6 @@
 from collections.abc import Sequence
 from typing import Any, Union
 
-from pydantic.v1 import BaseModel as BaseModel
-from pydantic.v1.fields import ModelField as ModelField
-
 
 def _regenerate_error_with_loc(
     *, errors: Sequence[Any], loc_prefix: tuple[Union[str, int], ...]

fastapi/_compat/shared.py

@@ -1,6 +1,7 @@
 import sys
 import types
 import typing
+import warnings
 from collections import deque
 from collections.abc import Mapping, Sequence
 from dataclasses import is_dataclass
@@ -10,7 +11,6 @@ from typing import (
     Union,
 )
 
-from fastapi._compat import may_v1
 from fastapi.types import UnionType
 from pydantic import BaseModel
 from pydantic.version import VERSION as PYDANTIC_VERSION
@@ -177,13 +177,27 @@ def is_uploadfile_sequence_annotation(annotation: Any) -> bool:
     )
 
 
+def is_pydantic_v1_model_instance(obj: Any) -> bool:
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore", UserWarning)
+        from pydantic import v1
+    return isinstance(obj, v1.BaseModel)
+
+
+def is_pydantic_v1_model_class(cls: Any) -> bool:
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore", UserWarning)
+        from pydantic import v1
+    return lenient_issubclass(cls, v1.BaseModel)
+
+
 def annotation_is_pydantic_v1(annotation: Any) -> bool:
-    if lenient_issubclass(annotation, may_v1.BaseModel):
+    if is_pydantic_v1_model_class(annotation):
         return True
     origin = get_origin(annotation)
     if origin is Union or origin is UnionType:
         for arg in get_args(annotation):
-            if lenient_issubclass(arg, may_v1.BaseModel):
+            if is_pydantic_v1_model_class(arg):
                 return True
     if field_annotation_is_sequence(annotation):
         for sub_annotation in get_args(annotation):

fastapi/encoders.py

@@ -25,7 +25,12 @@ from pydantic.color import Color
 from pydantic.networks import AnyUrl, NameEmail
 from pydantic.types import SecretBytes, SecretStr
 
-from ._compat import Url, _is_undefined, _model_dump, may_v1
+from ._compat import (
+    Url,
+    _is_undefined,
+    _model_dump,
+    is_pydantic_v1_model_instance,
+)
 
 
 # Taken from Pydantic v1 as is
@@ -218,7 +223,7 @@ def jsonable_encoder(
         include = set(include)
     if exclude is not None and not isinstance(exclude, (set, dict)):
         exclude = set(exclude)
-    if isinstance(obj, may_v1.BaseModel):
+    if is_pydantic_v1_model_instance(obj):
         raise PydanticV1NotSupportedError(
             "pydantic.v1 models are no longer supported by FastAPI."
             f" Please update the model {obj!r}."

tests/test_jsonable_encoder.py

@@ -1,3 +1,4 @@
+import warnings
 from collections import deque
 from dataclasses import dataclass
 from datetime import datetime, timezone
@@ -13,8 +14,6 @@ from fastapi.encoders import jsonable_encoder
 from fastapi.exceptions import PydanticV1NotSupportedError
 from pydantic import BaseModel, Field, ValidationError
 
-from .utils import needs_pydanticv1
-
 
 class Person:
     def __init__(self, name: str):
@@ -157,8 +156,9 @@ def test_encode_custom_json_encoders_model_pydanticv2():
     assert jsonable_encoder(subclass_model) == {"dt_field": "2019-01-01T08:00:00+00:00"}
 
 
-@needs_pydanticv1
 def test_json_encoder_error_with_pydanticv1():
+    with warnings.catch_warnings():
+        warnings.simplefilter("ignore", UserWarning)
         from pydantic import v1
 
     class ModelV1(v1.BaseModel):

tests/test_pydantic_v1_error.py

@@ -1,4 +1,5 @@
 import sys
+import warnings
 
 import pytest
 
@@ -8,9 +9,12 @@ if sys.version_info >= (3, 14):
     skip_module_if_py_gte_314()
 
 from fastapi import FastAPI
-from fastapi._compat.may_v1 import BaseModel
 from fastapi.exceptions import PydanticV1NotSupportedError
 
+with warnings.catch_warnings():
+    warnings.simplefilter("ignore", UserWarning)
+    from pydantic.v1 import BaseModel
+
 
 def test_raises_pydantic_v1_model_in_endpoint_param() -> None:
     class ParamModelV1(BaseModel):