Method from_annotated_attribute

pydantic/fields.py:379–477

Create `FieldInfo` from an annotation with a default value. This is used in cases like the following: ```python from typing import Annotated import annotated_types import pydantic class MyModel(pydantic.BaseModel): foo: int = 4 # <--

(
        annotation: type[Any], default: Any, *, _source: AnnotationSource = AnnotationSource.ANY
    )

    @staticmethod
    def from_annotated_attribute(
        annotation: type[Any], default: Any, *, _source: AnnotationSource = AnnotationSource.ANY
    ) -> FieldInfo:
        """Create `FieldInfo` from an annotation with a default value.

        This is used in cases like the following:

        ```python
        from typing import Annotated

        import annotated_types

        import pydantic

        class MyModel(pydantic.BaseModel):
            foo: int = 4  # <-- like this
            bar: Annotated[int, annotated_types.Gt(4)] = 4  # <-- or this
            spam: Annotated[int, pydantic.Field(gt=4)] = 4  # <-- or this
        ```

        Args:
            annotation: The type annotation of the field.
            default: The default value of the field.

        Returns:
            A field object with the passed values.
        """
        if annotation is not MISSING and annotation is default:
            raise PydanticUserError(
                'Error when building FieldInfo from annotated attribute. '
                "Make sure you don't have any field name clashing with a type annotation.",
                code='unevaluable-type-annotation',
            )

        try:
            inspected_ann = inspect_annotation(
                annotation,
                annotation_source=_source,
                unpack_type_aliases='skip',
            )
        except ForbiddenQualifier as e:
            raise PydanticForbiddenQualifier(e.qualifier, annotation)

        # TODO check for classvar and error?

        # TODO infer from the default, this can be done in v3 once we treat final fields with
        # a default as proper fields and not class variables:
        type_expr: Any = Any if inspected_ann.type is UNKNOWN else inspected_ann.type
        final = 'final' in inspected_ann.qualifiers
        metadata = inspected_ann.metadata

        # HACK 1: the order in which the metadata is merged is inconsistent; we need to prepend
        # metadata from the assignment at the beginning of the metadata. Changing this is only
        # possible in v3 (at least). See https://github.com/pydantic/pydantic/issues/10507
        prepend_metadata: list[Any] | None = None
        attr_overrides = {'annotation': type_expr}
        if final:
            attr_overrides['frozen'] = True