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Param

This class represents a parameter definition, inheriting from FieldInfo. It is used to define various characteristics and validation rules for input parameters, including default values, aliases, validation constraints (e.g., gt, min_length), and OpenAPI schema extensions. It supports features like example values, deprecation flags, and custom JSON schema extra fields.

Attributes​

AttributeTypeDescription
in_[ParamTypes](paramtypes.md?sid=fastapi_params_paramtypes)This attribute stores the type of parameter, which determines how the parameter's value is obtained and validated.

Constructor​

Signature​

def Param(
    default: Any = Undefined,
    default_factory: Callable[[], Any]| None = _Unset,
    annotation: Any | None = null,
    alias: str | None = null,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = null,
    serialization_alias: str | None = null,
    title: str | None = null,
    description: str | None = null,
    gt: float | None = null,
    ge: float | None = null,
    lt: float | None = null,
    le: float | None = null,
    min_length: int | None = null,
    max_length: int | None = null,
    pattern: str | None = null,
    regex: Annotated[str | None, deprecated("Deprecated in FastAPI 0.100.0 and Pydantic v2, use `pattern` instead.")] = null,
    discriminator: str | None = null,
    strict: bool | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    examples: list[Any]| None = null,
    example: Annotated[Any | None, deprecated("Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, although still supported. Use examples instead.")] = _Unset,
    openapi_examples: dict[str, [Example](../openapi/models/example.md?sid=fastapi_openapi_models_example)]| None = null,
    deprecated: deprecated | str | bool | None = null,
    include_in_schema: bool = True,
    json_schema_extra: dict[str, Any]| None = null,
    extra: Any = null
) - > null

Parameters​

NameTypeDescription
defaultAny = UndefinedThe default value for the parameter.
default_factory`Callable[[], Any]None` = _Unset
annotation`AnyNone` = null
alias`strNone` = null
alias_priority`intNone` = _Unset
validation_alias`strAliasPath
serialization_alias`strNone` = null
title`strNone` = null
description`strNone` = null
gt`floatNone` = null
ge`floatNone` = null
lt`floatNone` = null
le`floatNone` = null
min_length`intNone` = null
max_length`intNone` = null
pattern`strNone` = null
regex`Annotated[strNone, deprecated("Deprecated in FastAPI 0.100.0 and Pydantic v2, use pattern instead.")]` = null
discriminator`strNone` = null
strict`boolNone` = _Unset
multiple_of`floatNone` = _Unset
allow_inf_nan`boolNone` = _Unset
max_digits`intNone` = _Unset
decimal_places`intNone` = _Unset
examples`list[Any]None` = null
example`Annotated[AnyNone, deprecated("Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, although still supported. Use examples instead.")]` = _Unset
openapi_examples`dict[str, Example]None` = null
deprecated`deprecatedstr
include_in_schemabool = TrueWhether to include the parameter in the OpenAPI schema.
json_schema_extra`dict[str, Any]None` = null
extraAny = nullAdditional keyword arguments.

Signature​

def Param(
    default: Any = Undefined,
    default_factory: Callable[[], Any]| None = _Unset,
    annotation: Any | None = None,
    alias: str | None = None,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = None,
    serialization_alias: str | None = None,
    title: str | None = None,
    description: str | None = None,
    gt: float | None = None,
    ge: float | None = None,
    lt: float | None = None,
    le: float | None = None,
    min_length: int | None = None,
    max_length: int | None = None,
    pattern: str | None = None,
    regex: Annotated[str | None, deprecated("Deprecated in FastAPI 0.100.0 and Pydantic v2, use `pattern` instead.")] = None,
    discriminator: str | None = None,
    strict: bool | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    examples: list[Any]| None = None,
    example: Annotated[Any | None, deprecated("Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, although still supported. Use examples instead.")] = _Unset,
    openapi_examples: dict[str, [Example](../openapi/models/example.md?sid=fastapi_openapi_models_example)]| None = None,
    deprecated: deprecated | str | bool | None = None,
    include_in_schema: bool = True,
    json_schema_extra: dict[str, Any]| None = None,
    extra: Any
)

Parameters​

NameTypeDescription
defaultAny = UndefinedThe default value for the parameter if it is not provided.
default_factory`Callable[[], Any]None` = _Unset
annotation`AnyNone` = None
alias`strNone` = None
alias_priority`intNone` = _Unset
validation_alias`strAliasPath
serialization_alias`strNone` = None
title`strNone` = None
description`strNone` = None
gt`floatNone` = None
ge`floatNone` = None
lt`floatNone` = None
le`floatNone` = None
min_length`intNone` = None
max_length`intNone` = None
pattern`strNone` = None
regex`Annotated[strNone, deprecated("Deprecated in FastAPI 0.100.0 and Pydantic v2, use pattern instead.")]` = None
discriminator`strNone` = None
strict`boolNone` = _Unset
multiple_of`floatNone` = _Unset
allow_inf_nan`boolNone` = _Unset
max_digits`intNone` = _Unset
decimal_places`intNone` = _Unset
examples`list[Any]None` = None
example`Annotated[AnyNone, deprecated("Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, although still supported. Use examples instead.")]` = _Unset
openapi_examples`dict[str, Example]None` = None
deprecated`deprecatedstr
include_in_schemabool = TrueIf False, the parameter will not be included in the generated OpenAPI schema.
json_schema_extra`dict[str, Any]None` = None
extraAnyAdditional keyword arguments that will be passed through to the underlying FieldInfo.