🐛 Fix internal Pydantic v1 compatibility (warnings) for Python 3.14 and Pydantic 2.12.1 (#14186)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Sebastián Ramírez <[email protected]>

fastapi/_compat/__init__.py

@@ -30,6 +30,10 @@ from .main import serialize_sequence_value as serialize_sequence_value
 from .main import (
     with_info_plain_validator_function as with_info_plain_validator_function,
 )
+from .may_v1 import CoreSchema as CoreSchema
+from .may_v1 import GetJsonSchemaHandler as GetJsonSchemaHandler
+from .may_v1 import JsonSchemaValue as JsonSchemaValue
+from .may_v1 import _normalize_errors as _normalize_errors
 from .model_field import ModelField as ModelField
 from .shared import PYDANTIC_V2 as PYDANTIC_V2
 from .shared import PYDANTIC_VERSION_MINOR_TUPLE as PYDANTIC_VERSION_MINOR_TUPLE
@@ -44,7 +48,3 @@ from .shared import (
 from .shared import lenient_issubclass as lenient_issubclass
 from .shared import sequence_types as sequence_types
 from .shared import value_is_sequence as value_is_sequence
-from .v1 import CoreSchema as CoreSchema
-from .v1 import GetJsonSchemaHandler as GetJsonSchemaHandler
-from .v1 import JsonSchemaValue as JsonSchemaValue
-from .v1 import _normalize_errors as _normalize_errors

fastapi/_compat/main.py

@@ -1,3 +1,4 @@
+import sys
 from functools import lru_cache
 from typing import (
     Any,
@@ -8,7 +9,7 @@ from typing import (
     Type,
 )
 
-from fastapi._compat import v1
+from fastapi._compat import may_v1
 from fastapi._compat.shared import PYDANTIC_V2, lenient_issubclass
 from fastapi.types import ModelNameMap
 from pydantic import BaseModel
@@ -50,7 +51,9 @@ else:
 
 @lru_cache
 def get_cached_model_fields(model: Type[BaseModel]) -> List[ModelField]:
-    if lenient_issubclass(model, v1.BaseModel):
+    if lenient_issubclass(model, may_v1.BaseModel):
+        from fastapi._compat import v1
+
         return v1.get_model_fields(model)
     else:
         from . import v2
@@ -59,7 +62,7 @@ def get_cached_model_fields(model: Type[BaseModel]) -> List[ModelField]:
 
 
 def _is_undefined(value: object) -> bool:
-    if isinstance(value, v1.UndefinedType):
+    if isinstance(value, may_v1.UndefinedType):
         return True
     elif PYDANTIC_V2:
         from . import v2
@@ -69,7 +72,9 @@ def _is_undefined(value: object) -> bool:
 
 
 def _get_model_config(model: BaseModel) -> Any:
-    if isinstance(model, v1.BaseModel):
+    if isinstance(model, may_v1.BaseModel):
+        from fastapi._compat import v1
+
         return v1._get_model_config(model)
     elif PYDANTIC_V2:
         from . import v2
@@ -80,7 +85,9 @@ def _get_model_config(model: BaseModel) -> Any:
 def _model_dump(
     model: BaseModel, mode: Literal["json", "python"] = "json", **kwargs: Any
 ) -> Any:
-    if isinstance(model, v1.BaseModel):
+    if isinstance(model, may_v1.BaseModel):
+        from fastapi._compat import v1
+
         return v1._model_dump(model, mode=mode, **kwargs)
     elif PYDANTIC_V2:
         from . import v2
@@ -89,7 +96,7 @@ def _model_dump(
 
 
 def _is_error_wrapper(exc: Exception) -> bool:
-    if isinstance(exc, v1.ErrorWrapper):
+    if isinstance(exc, may_v1.ErrorWrapper):
         return True
     elif PYDANTIC_V2:
         from . import v2
@@ -99,7 +106,9 @@ def _is_error_wrapper(exc: Exception) -> bool:
 
 
 def copy_field_info(*, field_info: FieldInfo, annotation: Any) -> FieldInfo:
-    if isinstance(field_info, v1.FieldInfo):
+    if isinstance(field_info, may_v1.FieldInfo):
+        from fastapi._compat import v1
+
         return v1.copy_field_info(field_info=field_info, annotation=annotation)
     else:
         assert PYDANTIC_V2
@@ -111,7 +120,9 @@ def copy_field_info(*, field_info: FieldInfo, annotation: Any) -> FieldInfo:
 def create_body_model(
     *, fields: Sequence[ModelField], model_name: str
 ) -> Type[BaseModel]:
-    if fields and isinstance(fields[0], v1.ModelField):
+    if fields and isinstance(fields[0], may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.create_body_model(fields=fields, model_name=model_name)
     else:
         assert PYDANTIC_V2
@@ -123,7 +134,9 @@ def create_body_model(
 def get_annotation_from_field_info(
     annotation: Any, field_info: FieldInfo, field_name: str
 ) -> Any:
-    if isinstance(field_info, v1.FieldInfo):
+    if isinstance(field_info, may_v1.FieldInfo):
+        from fastapi._compat import v1
+
         return v1.get_annotation_from_field_info(
             annotation=annotation, field_info=field_info, field_name=field_name
         )
@@ -137,7 +150,9 @@ def get_annotation_from_field_info(
 
 
 def is_bytes_field(field: ModelField) -> bool:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.is_bytes_field(field)
     else:
         assert PYDANTIC_V2
@@ -147,7 +162,9 @@ def is_bytes_field(field: ModelField) -> bool:
 
 
 def is_bytes_sequence_field(field: ModelField) -> bool:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.is_bytes_sequence_field(field)
     else:
         assert PYDANTIC_V2
@@ -157,7 +174,9 @@ def is_bytes_sequence_field(field: ModelField) -> bool:
 
 
 def is_scalar_field(field: ModelField) -> bool:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.is_scalar_field(field)
     else:
         assert PYDANTIC_V2
@@ -167,7 +186,9 @@ def is_scalar_field(field: ModelField) -> bool:
 
 
 def is_scalar_sequence_field(field: ModelField) -> bool:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.is_scalar_sequence_field(field)
     else:
         assert PYDANTIC_V2
@@ -177,7 +198,9 @@ def is_scalar_sequence_field(field: ModelField) -> bool:
 
 
 def is_sequence_field(field: ModelField) -> bool:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.is_sequence_field(field)
     else:
         assert PYDANTIC_V2
@@ -187,7 +210,9 @@ def is_sequence_field(field: ModelField) -> bool:
 
 
 def serialize_sequence_value(*, field: ModelField, value: Any) -> Sequence[Any]:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.serialize_sequence_value(field=field, value=value)
     else:
         assert PYDANTIC_V2
@@ -197,7 +222,9 @@ def serialize_sequence_value(*, field: ModelField, value: Any) -> Sequence[Any]:
 
 
 def _model_rebuild(model: Type[BaseModel]) -> None:
-    if lenient_issubclass(model, v1.BaseModel):
+    if lenient_issubclass(model, may_v1.BaseModel):
+        from fastapi._compat import v1
+
         v1._model_rebuild(model)
     elif PYDANTIC_V2:
         from . import v2
@@ -206,9 +233,18 @@ def _model_rebuild(model: Type[BaseModel]) -> None:
 
 
 def get_compat_model_name_map(fields: List[ModelField]) -> ModelNameMap:
-    v1_model_fields = [field for field in fields if isinstance(field, v1.ModelField)]
+    v1_model_fields = [
-    v1_flat_models = v1.get_flat_models_from_fields(v1_model_fields, known_models=set())  # type: ignore[attr-defined]
+        field for field in fields if isinstance(field, may_v1.ModelField)
-    all_flat_models = v1_flat_models
+    ]
+    if v1_model_fields:
+        from fastapi._compat import v1
+
+        v1_flat_models = v1.get_flat_models_from_fields(
+            v1_model_fields, known_models=set()
+        )
+        all_flat_models = v1_flat_models
+    else:
+        all_flat_models = set()
     if PYDANTIC_V2:
         from . import v2
 
@@ -222,6 +258,8 @@ def get_compat_model_name_map(fields: List[ModelField]) -> ModelNameMap:
 
         model_name_map = v2.get_model_name_map(all_flat_models)
         return model_name_map
+    from fastapi._compat import v1
+
     model_name_map = v1.get_model_name_map(all_flat_models)
     return model_name_map
 
@@ -232,17 +270,35 @@ def get_definitions(
     model_name_map: ModelNameMap,
     separate_input_output_schemas: bool = True,
 ) -> Tuple[
-    Dict[Tuple[ModelField, Literal["validation", "serialization"]], v1.JsonSchemaValue],
+    Dict[
+        Tuple[ModelField, Literal["validation", "serialization"]],
+        may_v1.JsonSchemaValue,
+    ],
     Dict[str, Dict[str, Any]],
 ]:
-    v1_fields = [field for field in fields if isinstance(field, v1.ModelField)]
+    if sys.version_info < (3, 14):
-    v1_field_maps, v1_definitions = v1.get_definitions(
+        v1_fields = [field for field in fields if isinstance(field, may_v1.ModelField)]
-        fields=v1_fields,
+        v1_field_maps, v1_definitions = may_v1.get_definitions(
-        model_name_map=model_name_map,
+            fields=v1_fields,
-        separate_input_output_schemas=separate_input_output_schemas,
+            model_name_map=model_name_map,
-    )
+            separate_input_output_schemas=separate_input_output_schemas,
-    if not PYDANTIC_V2:
+        )
-        return v1_field_maps, v1_definitions
+        if not PYDANTIC_V2:
+            return v1_field_maps, v1_definitions
+        else:
+            from . import v2
+
+            v2_fields = [field for field in fields if isinstance(field, v2.ModelField)]
+            v2_field_maps, v2_definitions = v2.get_definitions(
+                fields=v2_fields,
+                model_name_map=model_name_map,
+                separate_input_output_schemas=separate_input_output_schemas,
+            )
+            all_definitions = {**v1_definitions, **v2_definitions}
+            all_field_maps = {**v1_field_maps, **v2_field_maps}
+            return all_field_maps, all_definitions
+
+    # Pydantic v1 is not supported since Python 3.14
     else:
         from . import v2
 
@@ -252,9 +308,7 @@ def get_definitions(
             model_name_map=model_name_map,
             separate_input_output_schemas=separate_input_output_schemas,
         )
-        all_definitions = {**v1_definitions, **v2_definitions}
+        return v2_field_maps, v2_definitions
-        all_field_maps = {**v1_field_maps, **v2_field_maps}
-        return all_field_maps, all_definitions
 
 
 def get_schema_from_model_field(
@@ -262,11 +316,14 @@ def get_schema_from_model_field(
     field: ModelField,
     model_name_map: ModelNameMap,
     field_mapping: Dict[
-        Tuple[ModelField, Literal["validation", "serialization"]], v1.JsonSchemaValue
+        Tuple[ModelField, Literal["validation", "serialization"]],
+        may_v1.JsonSchemaValue,
     ],
     separate_input_output_schemas: bool = True,
 ) -> Dict[str, Any]:
-    if isinstance(field, v1.ModelField):
+    if isinstance(field, may_v1.ModelField):
+        from fastapi._compat import v1
+
         return v1.get_schema_from_model_field(
             field=field,
             model_name_map=model_name_map,
@@ -286,7 +343,7 @@ def get_schema_from_model_field(
 
 
 def _is_model_field(value: Any) -> bool:
-    if isinstance(value, v1.ModelField):
+    if isinstance(value, may_v1.ModelField):
         return True
     elif PYDANTIC_V2:
         from . import v2
@@ -296,7 +353,7 @@ def _is_model_field(value: Any) -> bool:
 
 
 def _is_model_class(value: Any) -> bool:
-    if lenient_issubclass(value, v1.BaseModel):
+    if lenient_issubclass(value, may_v1.BaseModel):
         return True
     elif PYDANTIC_V2:
         from . import v2

fastapi/_compat/may_v1.py

@@ -0,0 +1,123 @@
+import sys
+from typing import Any, Dict, List, Literal, Sequence, Tuple, Type, Union
+
+from fastapi.types import ModelNameMap
+
+if sys.version_info >= (3, 14):
+
+    class AnyUrl:
+        pass
+
+    class BaseConfig:
+        pass
+
+    class BaseModel:
+        pass
+
+    class Color:
+        pass
+
+    class CoreSchema:
+        pass
+
+    class ErrorWrapper:
+        pass
+
+    class FieldInfo:
+        pass
+
+    class GetJsonSchemaHandler:
+        pass
+
+    class JsonSchemaValue:
+        pass
+
+    class ModelField:
+        pass
+
+    class NameEmail:
+        pass
+
+    class RequiredParam:
+        pass
+
+    class SecretBytes:
+        pass
+
+    class SecretStr:
+        pass
+
+    class Undefined:
+        pass
+
+    class UndefinedType:
+        pass
+
+    class Url:
+        pass
+
+    from .v2 import ValidationError, create_model
+
+    def get_definitions(
+        *,
+        fields: List[ModelField],
+        model_name_map: ModelNameMap,
+        separate_input_output_schemas: bool = True,
+    ) -> Tuple[
+        Dict[
+            Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue
+        ],
+        Dict[str, Dict[str, Any]],
+    ]:
+        return {}, {}  # pragma: no cover
+
+
+else:
+    from .v1 import AnyUrl as AnyUrl
+    from .v1 import BaseConfig as BaseConfig
+    from .v1 import BaseModel as BaseModel
+    from .v1 import Color as Color
+    from .v1 import CoreSchema as CoreSchema
+    from .v1 import ErrorWrapper as ErrorWrapper
+    from .v1 import FieldInfo as FieldInfo
+    from .v1 import GetJsonSchemaHandler as GetJsonSchemaHandler
+    from .v1 import JsonSchemaValue as JsonSchemaValue
+    from .v1 import ModelField as ModelField
+    from .v1 import NameEmail as NameEmail
+    from .v1 import RequiredParam as RequiredParam
+    from .v1 import SecretBytes as SecretBytes
+    from .v1 import SecretStr as SecretStr
+    from .v1 import Undefined as Undefined
+    from .v1 import UndefinedType as UndefinedType
+    from .v1 import Url as Url
+    from .v1 import ValidationError, create_model
+    from .v1 import get_definitions as get_definitions
+
+
+RequestErrorModel: Type[BaseModel] = create_model("Request")
+
+
+def _normalize_errors(errors: Sequence[Any]) -> List[Dict[str, Any]]:
+    use_errors: List[Any] = []
+    for error in errors:
+        if isinstance(error, ErrorWrapper):
+            new_errors = ValidationError(  # type: ignore[call-arg]
+                errors=[error], model=RequestErrorModel
+            ).errors()
+            use_errors.extend(new_errors)
+        elif isinstance(error, list):
+            use_errors.extend(_normalize_errors(error))
+        else:
+            use_errors.append(error)
+    return use_errors
+
+
+def _regenerate_error_with_loc(
+    *, errors: Sequence[Any], loc_prefix: Tuple[Union[str, int], ...]
+) -> List[Dict[str, Any]]:
+    updated_loc_errors: List[Any] = [
+        {**err, "loc": loc_prefix + err.get("loc", ())}
+        for err in _normalize_errors(errors)
+    ]
+
+    return updated_loc_errors

fastapi/_compat/shared.py

@@ -16,7 +16,7 @@ from typing import (
     Union,
 )
 
-from fastapi._compat import v1
+from fastapi._compat import may_v1
 from fastapi.types import UnionType
 from pydantic import BaseModel
 from pydantic.version import VERSION as PYDANTIC_VERSION
@@ -98,7 +98,9 @@ def value_is_sequence(value: Any) -> bool:
 
 def _annotation_is_complex(annotation: Union[Type[Any], None]) -> bool:
     return (
-        lenient_issubclass(annotation, (BaseModel, v1.BaseModel, Mapping, UploadFile))
+        lenient_issubclass(
+            annotation, (BaseModel, may_v1.BaseModel, Mapping, UploadFile)
+        )
         or _annotation_is_sequence(annotation)
         or is_dataclass(annotation)
     )
@@ -195,12 +197,12 @@ def is_uploadfile_sequence_annotation(annotation: Any) -> bool:
 
 
 def annotation_is_pydantic_v1(annotation: Any) -> bool:
-    if lenient_issubclass(annotation, v1.BaseModel):
+    if lenient_issubclass(annotation, may_v1.BaseModel):
         return True
     origin = get_origin(annotation)
     if origin is Union or origin is UnionType:
         for arg in get_args(annotation):
-            if lenient_issubclass(arg, v1.BaseModel):
+            if lenient_issubclass(arg, may_v1.BaseModel):
                 return True
     if field_annotation_is_sequence(annotation):
         for sub_annotation in get_args(annotation):

fastapi/_compat/v1.py

@@ -54,13 +54,15 @@ if not PYDANTIC_V2:
     from pydantic.schema import TypeModelSet as TypeModelSet
     from pydantic.schema import (
         field_schema,
-        get_flat_models_from_fields,
         model_process_schema,
     )
     from pydantic.schema import (
         get_annotation_from_field_info as get_annotation_from_field_info,
     )
     from pydantic.schema import get_flat_models_from_field as get_flat_models_from_field
+    from pydantic.schema import (
+        get_flat_models_from_fields as get_flat_models_from_fields,
+    )
     from pydantic.schema import get_model_name_map as get_model_name_map
     from pydantic.types import SecretBytes as SecretBytes
     from pydantic.types import SecretStr as SecretStr
@@ -99,7 +101,6 @@ else:
     from pydantic.v1.schema import TypeModelSet as TypeModelSet
     from pydantic.v1.schema import (
         field_schema,
-        get_flat_models_from_fields,
         model_process_schema,
     )
     from pydantic.v1.schema import (
@@ -108,6 +109,9 @@ else:
     from pydantic.v1.schema import (
         get_flat_models_from_field as get_flat_models_from_field,
     )
+    from pydantic.v1.schema import (
+        get_flat_models_from_fields as get_flat_models_from_fields,
+    )
     from pydantic.v1.schema import get_model_name_map as get_model_name_map
     from pydantic.v1.types import (  # type: ignore[assignment]
         SecretBytes as SecretBytes,
@@ -215,32 +219,6 @@ def is_pv1_scalar_sequence_field(field: ModelField) -> bool:
     return False
 
 
-def _normalize_errors(errors: Sequence[Any]) -> List[Dict[str, Any]]:
-    use_errors: List[Any] = []
-    for error in errors:
-        if isinstance(error, ErrorWrapper):
-            new_errors = ValidationError(  # type: ignore[call-arg]
-                errors=[error], model=RequestErrorModel
-            ).errors()
-            use_errors.extend(new_errors)
-        elif isinstance(error, list):
-            use_errors.extend(_normalize_errors(error))
-        else:
-            use_errors.append(error)
-    return use_errors
-
-
-def _regenerate_error_with_loc(
-    *, errors: Sequence[Any], loc_prefix: Tuple[Union[str, int], ...]
-) -> List[Dict[str, Any]]:
-    updated_loc_errors: List[Any] = [
-        {**err, "loc": loc_prefix + err.get("loc", ())}
-        for err in _normalize_errors(errors)
-    ]
-
-    return updated_loc_errors
-
-
 def _model_rebuild(model: Type[BaseModel]) -> None:
     model.update_forward_refs()
 

fastapi/_compat/v2.py

@@ -15,7 +15,7 @@ from typing import (
     cast,
 )
 
-from fastapi._compat import shared, v1
+from fastapi._compat import may_v1, shared
 from fastapi.openapi.constants import REF_TEMPLATE
 from fastapi.types import IncEx, ModelNameMap
 from pydantic import BaseModel, TypeAdapter, create_model
@@ -116,7 +116,7 @@ class ModelField:
                 None,
             )
         except ValidationError as exc:
-            return None, v1._regenerate_error_with_loc(
+            return None, may_v1._regenerate_error_with_loc(
                 errors=exc.errors(include_url=False), loc_prefix=loc
             )
 

fastapi/dependencies/utils.py

@@ -43,9 +43,9 @@ from fastapi._compat import (
     is_uploadfile_or_nonable_uploadfile_annotation,
     is_uploadfile_sequence_annotation,
     lenient_issubclass,
+    may_v1,
     sequence_types,
     serialize_sequence_value,
-    v1,
     value_is_sequence,
 )
 from fastapi._compat.shared import annotation_is_pydantic_v1
@@ -380,7 +380,7 @@ def analyze_param(
         fastapi_annotations = [
             arg
             for arg in annotated_args[1:]
-            if isinstance(arg, (FieldInfo, v1.FieldInfo, params.Depends))
+            if isinstance(arg, (FieldInfo, may_v1.FieldInfo, params.Depends))
         ]
         fastapi_specific_annotations = [
             arg
@@ -397,21 +397,21 @@ def analyze_param(
             )
         ]
         if fastapi_specific_annotations:
-            fastapi_annotation: Union[FieldInfo, v1.FieldInfo, params.Depends, None] = (
+            fastapi_annotation: Union[
-                fastapi_specific_annotations[-1]
+                FieldInfo, may_v1.FieldInfo, params.Depends, None
-            )
+            ] = fastapi_specific_annotations[-1]
         else:
             fastapi_annotation = None
         # Set default for Annotated FieldInfo
-        if isinstance(fastapi_annotation, (FieldInfo, v1.FieldInfo)):
+        if isinstance(fastapi_annotation, (FieldInfo, may_v1.FieldInfo)):
             # Copy `field_info` because we mutate `field_info.default` below.
             field_info = copy_field_info(
                 field_info=fastapi_annotation, annotation=use_annotation
             )
             assert field_info.default in {
                 Undefined,
-                v1.Undefined,
+                may_v1.Undefined,
-            } or field_info.default in {RequiredParam, v1.RequiredParam}, (
+            } or field_info.default in {RequiredParam, may_v1.RequiredParam}, (
                 f"`{field_info.__class__.__name__}` default value cannot be set in"
                 f" `Annotated` for {param_name!r}. Set the default value with `=` instead."
             )
@@ -435,7 +435,7 @@ def analyze_param(
         )
         depends = value
     # Get FieldInfo from default value
-    elif isinstance(value, (FieldInfo, v1.FieldInfo)):
+    elif isinstance(value, (FieldInfo, may_v1.FieldInfo)):
         assert field_info is None, (
             "Cannot specify FastAPI annotations in `Annotated` and default value"
             f" together for {param_name!r}"
@@ -524,7 +524,8 @@ def analyze_param(
             type_=use_annotation_from_field_info,
             default=field_info.default,
             alias=alias,
-            required=field_info.default in (RequiredParam, v1.RequiredParam, Undefined),
+            required=field_info.default
+            in (RequiredParam, may_v1.RequiredParam, Undefined),
             field_info=field_info,
         )
         if is_path_param:
@@ -741,7 +742,7 @@ def _validate_value_with_model_field(
     if _is_error_wrapper(errors_):  # type: ignore[arg-type]
         return None, [errors_]
     elif isinstance(errors_, list):
-        new_errors = v1._regenerate_error_with_loc(errors=errors_, loc_prefix=())
+        new_errors = may_v1._regenerate_error_with_loc(errors=errors_, loc_prefix=())
         return None, new_errors
     else:
         return v_, []

fastapi/encoders.py

@@ -17,7 +17,7 @@ from types import GeneratorType
 from typing import Any, Callable, Dict, List, Optional, Tuple, Type, Union
 from uuid import UUID
 
-from fastapi._compat import v1
+from fastapi._compat import may_v1
 from fastapi.types import IncEx
 from pydantic import BaseModel
 from pydantic.color import Color
@@ -59,7 +59,7 @@ def decimal_encoder(dec_value: Decimal) -> Union[int, float]:
 ENCODERS_BY_TYPE: Dict[Type[Any], Callable[[Any], Any]] = {
     bytes: lambda o: o.decode(),
     Color: str,
-    v1.Color: str,
+    may_v1.Color: str,
     datetime.date: isoformat,
     datetime.datetime: isoformat,
     datetime.time: isoformat,
@@ -76,19 +76,19 @@ ENCODERS_BY_TYPE: Dict[Type[Any], Callable[[Any], Any]] = {
     IPv6Interface: str,
     IPv6Network: str,
     NameEmail: str,
-    v1.NameEmail: str,
+    may_v1.NameEmail: str,
     Path: str,
     Pattern: lambda o: o.pattern,
     SecretBytes: str,
-    v1.SecretBytes: str,
+    may_v1.SecretBytes: str,
     SecretStr: str,
-    v1.SecretStr: str,
+    may_v1.SecretStr: str,
     set: list,
     UUID: str,
     Url: str,
-    v1.Url: str,
+    may_v1.Url: str,
     AnyUrl: str,
-    v1.AnyUrl: str,
+    may_v1.AnyUrl: str,
 }
 
 
@@ -220,10 +220,10 @@ def jsonable_encoder(
         include = set(include)
     if exclude is not None and not isinstance(exclude, (set, dict)):
         exclude = set(exclude)
-    if isinstance(obj, (BaseModel, v1.BaseModel)):
+    if isinstance(obj, (BaseModel, may_v1.BaseModel)):
         # TODO: remove when deprecating Pydantic v1
         encoders: Dict[Any, Any] = {}
-        if isinstance(obj, v1.BaseModel):
+        if isinstance(obj, may_v1.BaseModel):
             encoders = getattr(obj.__config__, "json_encoders", {})  # type: ignore[attr-defined]
             if custom_encoder:
                 encoders = {**encoders, **custom_encoder}

fastapi/temp_pydantic_v1_params.py

@@ -5,8 +5,8 @@ from fastapi.openapi.models import Example
 from fastapi.params import ParamTypes
 from typing_extensions import Annotated, deprecated
 
+from ._compat.may_v1 import FieldInfo, Undefined
 from ._compat.shared import PYDANTIC_VERSION_MINOR_TUPLE
-from ._compat.v1 import FieldInfo, Undefined
 
 _Unset: Any = Undefined
 

fastapi/utils.py

@@ -25,7 +25,7 @@ from fastapi._compat import (
     Validator,
     annotation_is_pydantic_v1,
     lenient_issubclass,
-    v1,
+    may_v1,
 )
 from fastapi.datastructures import DefaultPlaceholder, DefaultType
 from pydantic import BaseModel
@@ -87,8 +87,8 @@ def create_model_field(
 ) -> ModelField:
     class_validators = class_validators or {}
 
-    v1_model_config = v1.BaseConfig
+    v1_model_config = may_v1.BaseConfig
-    v1_field_info = field_info or v1.FieldInfo()
+    v1_field_info = field_info or may_v1.FieldInfo()
     v1_kwargs = {
         "name": name,
         "field_info": v1_field_info,
@@ -102,9 +102,11 @@ def create_model_field(
 
     if (
         annotation_is_pydantic_v1(type_)
-        or isinstance(field_info, v1.FieldInfo)
+        or isinstance(field_info, may_v1.FieldInfo)
         or version == "1"
     ):
+        from fastapi._compat import v1
+
         try:
             return v1.ModelField(**v1_kwargs)  # type: ignore[no-any-return]
         except RuntimeError:
@@ -122,6 +124,8 @@ def create_model_field(
             raise fastapi.exceptions.FastAPIError(_invalid_args_message) from None
     # Pydantic v2 is not installed, but it's not a Pydantic v1 ModelField, it could be
     # a Pydantic v1 type, like a constrained int
+    from fastapi._compat import v1
+
     try:
         return v1.ModelField(**v1_kwargs)  # type: ignore[no-any-return]
     except RuntimeError:
@@ -138,6 +142,9 @@ def create_cloned_field(
 
         if isinstance(field, v2.ModelField):
             return field
+
+    from fastapi._compat import v1
+
     # cloned_types caches already cloned types to support recursive models and improve
     # performance by avoiding unnecessary cloning
     if cloned_types is None:

tests/test_compat.py

@@ -7,7 +7,7 @@ from fastapi._compat import (
     get_cached_model_fields,
     is_scalar_field,
     is_uploadfile_sequence_annotation,
-    v1,
+    may_v1,
 )
 from fastapi._compat.shared import is_bytes_sequence_annotation
 from fastapi.testclient import TestClient
@@ -27,7 +27,10 @@ def test_model_field_default_required():
     assert field.default is Undefined
 
 
+@needs_py_lt_314
 def test_v1_plain_validator_function():
+    from fastapi._compat import v1
+
     # For coverage
     def func(v):  # pragma: no cover
         return v
@@ -135,6 +138,8 @@ def test_is_uploadfile_sequence_annotation():
 
 @needs_py_lt_314
 def test_is_pv1_scalar_field():
+    from fastapi._compat import v1
+
     # For coverage
     class Model(v1.BaseModel):
         foo: Union[str, Dict[str, Any]]
@@ -143,8 +148,11 @@ def test_is_pv1_scalar_field():
     assert not is_scalar_field(fields[0])
 
 
+@needs_py_lt_314
 def test_get_model_fields_cached():
-    class Model(v1.BaseModel):
+    from fastapi._compat import v1
+
+    class Model(may_v1.BaseModel):
         foo: str
 
     non_cached_fields = v1.get_model_fields(Model)

tests/test_get_model_definitions_formfeed_escape.py

@@ -5,7 +5,6 @@ import fastapi.openapi.utils
 import pydantic.schema
 import pytest
 from fastapi import FastAPI
-from fastapi._compat import v1
 from pydantic import BaseModel
 from starlette.testclient import TestClient
 
@@ -165,6 +164,8 @@ def test_model_description_escaped_with_formfeed(sort_reversed: bool):
 
     Test `get_model_definitions` with models passed in different order.
     """
+    from fastapi._compat import v1
+
     all_fields = fastapi.openapi.utils.get_fields_from_routes(app.routes)
 
     flat_models = v1.get_flat_models_from_fields(all_fields, known_models=set())

tests/test_response_model_as_return_annotation.py

@@ -2,12 +2,13 @@ from typing import List, Union
 
 import pytest
 from fastapi import FastAPI
-from fastapi._compat import v1
 from fastapi.exceptions import FastAPIError, ResponseValidationError
 from fastapi.responses import JSONResponse, Response
 from fastapi.testclient import TestClient
 from pydantic import BaseModel
 
+from tests.utils import needs_pydanticv1
+
 
 class BaseUser(BaseModel):
     name: str
@@ -511,7 +512,10 @@ def test_invalid_response_model_field():
 
 
 # TODO: remove when dropping Pydantic v1 support
+@needs_pydanticv1
 def test_invalid_response_model_field_pv1():
+    from fastapi._compat import v1
+
     app = FastAPI()
 
     class Model(v1.BaseModel):