Method from_annotation

pydantic/fields.py:319–376

Creates a `FieldInfo` instance from a bare annotation. This function is used internally to create a `FieldInfo` from a bare annotation like this: ```python import pydantic class MyModel(pydantic.BaseModel): foo: int # <-- like this ```

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

    @staticmethod
    def from_annotation(annotation: type[Any], *, _source: AnnotationSource = AnnotationSource.ANY) -> FieldInfo:
        """Creates a `FieldInfo` instance from a bare annotation.

        This function is used internally to create a `FieldInfo` from a bare annotation like this:

        ```python
        import pydantic

        class MyModel(pydantic.BaseModel):
            foo: int  # <-- like this
        ```

        We also account for the case where the annotation can be an instance of `Annotated` and where
        one of the (not first) arguments in `Annotated` is an instance of `FieldInfo`, e.g.:

        ```python
        from typing import Annotated

        import annotated_types

        import pydantic

        class MyModel(pydantic.BaseModel):
            foo: Annotated[int, annotated_types.Gt(42)]
            bar: Annotated[int, pydantic.Field(gt=42)]
        ```

        Args:
            annotation: An annotation object.

        Returns:
            An instance of the field metadata.
        """
        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?

        # No assigned value, this happens when using a bare `Final` qualifier (also for other
        # qualifiers, but they shouldn't appear here). In this case we infer the type as `Any`
        # because we don't have any assigned value.
        type_expr: Any = Any if inspected_ann.type is UNKNOWN else inspected_ann.type
        final = 'final' in inspected_ann.qualifiers
        metadata = inspected_ann.metadata

        attr_overrides = {'annotation': type_expr}
        if final:
            attr_overrides['frozen'] = True
        field_info = FieldInfo._construct(metadata, **attr_overrides)
        field_info._qualifiers = inspected_ann.qualifiers
        field_info._final = True
        return field_info