Class FieldInfo

pydantic/fields.py:106–869

This class holds information about a field. `FieldInfo` is used for any field definition regardless of whether the [`Field()`][pydantic.fields.Field] function is explicitly used. !!! warning The `FieldInfo` class is meant to expose information about a field in a Pydantic model

@final
class FieldInfo(_repr.Representation):
    """This class holds information about a field.

    `FieldInfo` is used for any field definition regardless of whether the [`Field()`][pydantic.fields.Field]
    function is explicitly used.

    !!! warning
        The `FieldInfo` class is meant to expose information about a field in a Pydantic model or dataclass.
        `FieldInfo` instances shouldn't be instantiated directly, nor mutated.

        If you need to derive a new model from another one and are willing to alter `FieldInfo` instances,
        refer to this [dynamic model example](../examples/dynamic_models.md).

    Attributes:
        annotation: The type annotation of the field.
        default: The default value of the field.
        default_factory: A callable to generate the default value. The callable can either take 0 arguments
            (in which case it is called as is) or a single argument containing the already validated data.
        alias: The alias name of the field.
        alias_priority: The priority of the field's alias.
        validation_alias: The validation alias of the field.
        serialization_alias: The serialization alias of the field.
        title: The title of the field.
        field_title_generator: A callable that takes a field name and returns title for it.
        description: The description of the field.
        examples: List of examples of the field.
        exclude: Whether to exclude the field from the model serialization.
        exclude_if: A callable that determines whether to exclude a field during serialization based on its value.
        discriminator: Field name or Discriminator for discriminating the type in a tagged union.
        deprecated: A deprecation message, an instance of `warnings.deprecated` or the `typing_extensions.deprecated` backport,
            or a boolean. If `True`, a default deprecation message will be emitted when accessing the field.
        json_schema_extra: A dict or callable to provide extra JSON schema properties.
        frozen: Whether the field is frozen.
        validate_default: Whether to validate the default value of the field.
        repr: Whether to include the field in representation of the model.
        init: Whether the field should be included in the constructor of the dataclass.
        init_var: Whether the field should _only_ be included in the constructor of the dataclass, and not stored.
        kw_only: Whether the field should be a keyword-only argument in the constructor of the dataclass.
        metadata: The metadata list. Contains all the data that isn't expressed as direct `FieldInfo` attributes, including:

            * Type-specific constraints, such as `gt` or `min_length` (these are converted to metadata classes such as `annotated_types.Gt`).
            * Any other arbitrary object used within [`Annotated`][typing.Annotated] metadata
              (e.g. [custom types handlers](../concepts/types.md#as-an-annotation) or any object not recognized by Pydantic).
    """

    # TODO PEP 747: use TypeForm:
    annotation: type[Any] | None
    default: Any
    default_factory: Callable[[], Any] | Callable[[dict[str, Any]], Any] | None
    alias: str | None
    alias_priority: int | None
    validation_alias: str | AliasPath | AliasChoices | None
    serialization_alias: str | None
    title: str | None
    field_title_generator: Callable[[str, FieldInfo], str] | None
    description: str | None
    examples: list[Any] | None
    exclude: bool | None