Field#

!!! abstract “Usage Documentation”: [Fields](../concepts/fields.md)

Create a field for objects that can be configured.

Used to provide extra information about a field, either for the model schema or complex validation. Some arguments apply only to number fields (int, float, Decimal) and some apply only to str.

Note:

Any _Unset objects will be replaced by the corresponding value defined in the _DefaultValues dictionary. If a key for the _Unset object is not found in the _DefaultValues dictionary, it will default to None

Args:

default: Default value if the field is not set. 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 name to use for the attribute when validating or serializing by alias.: This is often used for things like converting between snake and camel case.

alias_priority: Priority of the alias. This affects whether an alias generator is used. validation_alias: Like alias, but only affects validation, not serialization. serialization_alias: Like alias, but only affects serialization, not validation. title: Human-readable title. field_title_generator: A callable that takes a field name and returns title for it. description: Human-readable description. examples: Example values for this 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. If true, attempts to change the value on an instance will raise an error. validate_default: If True, apply validation to the default value every time you create an instance.

Otherwise, for performance reasons, the default value of the field is trusted and not validated.

repr: A boolean indicating whether to include the field in the __repr__ output. init: Whether the field should be included in the constructor of the dataclass.

(Only applies to dataclasses.)

init_var: Whether the field should _only_ be included in the constructor of the dataclass.: (Only applies to dataclasses.)
kw_only: Whether the field should be a keyword-only argument in the constructor of the dataclass.: (Only applies to dataclasses.)

coerce_numbers_to_str: Whether to enable coercion of any Number type to str (not applicable in strict mode). strict: If True, strict validation is applied to the field.

See [Strict Mode](../concepts/strict_mode.md) for details.

gt: Greater than. If set, value must be greater than this. Only applicable to numbers. ge: Greater than or equal. If set, value must be greater than or equal to this. Only applicable to numbers. lt: Less than. If set, value must be less than this. Only applicable to numbers. le: Less than or equal. If set, value must be less than or equal to this. Only applicable to numbers. multiple_of: Value must be a multiple of this. Only applicable to numbers. min_length: Minimum length for iterables. max_length: Maximum length for iterables. pattern: Pattern for strings (a regular expression). allow_inf_nan: Allow inf, -inf, nan. Only applicable to float and [Decimal][decimal.Decimal] numbers. max_digits: Maximum number of allow digits for strings. decimal_places: Maximum number of decimal places allowed for numbers. union_mode: The strategy to apply when validating a union. Can be smart (the default), or left_to_right.

See [Union Mode](../concepts/unions.md#union-modes) for details.

fail_fast: If True, validation will stop on the first error. If False, all validation errors will be collected.: This option can be applied only to iterable types (list, tuple, set, and frozenset).

extra: (Deprecated) Extra fields that will be included in the JSON schema.

!!! warning Deprecated
The extra kwargs is deprecated. Use json_schema_extra instead.

Returns:

A new [FieldInfo][pydantic.fields.FieldInfo]. The return annotation is Any so Field can be used on: type-annotated fields without causing a type error.

Parameters:

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)
exclude_if (Callable[[Any], bool] | None)
discriminator (str | types.Discriminator | None)
deprecated (Deprecated | str | bool | None)
json_schema_extra (JsonDict | Callable[[JsonDict], None] | None)
frozen (bool | None)
validate_default (bool | None)
repr (bool)
init (bool | None)
init_var (bool | None)
kw_only (bool | None)
pattern (str | re.Pattern[str] | None)
strict (bool | None)
coerce_numbers_to_str (bool | None)
gt (annotated_types.SupportsGt | None)
ge (annotated_types.SupportsGe | None)
lt (annotated_types.SupportsLt | None)
le (annotated_types.SupportsLe | None)
multiple_of (float | None)
allow_inf_nan (bool | None)
max_digits (int | None)
decimal_places (int | None)
min_length (int | None)
max_length (int | None)
union_mode (Literal['smart', 'left_to_right'])
fail_fast (bool | None)
extra (Unpack[_EmptyKwargs])

Return type:

Any