Defining fields on models.

## FieldInfo

**Bases:** `Representation`

This class holds information about a field.

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

:::callout{intent="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](/guides/examples-dynamic-models).
:::

### Attributes

#### annotation

The type annotation of the field.

**Type:** [`type`](https://docs.python.org/3/glossary.html#term-type)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### default

The default value of the field.

**Type:** [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)

#### 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.

**Type:** [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[], [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`dict`](https://docs.python.org/3/reference/expressions.html#dict)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]], [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### alias

The alias name of the field.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### alias\_priority

The priority of the field’s alias.

**Type:** [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### validation\_alias

The validation alias of the field.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`AliasPath`](/guides/pydantic-aliases#aliaspath) | [`AliasChoices`](/guides/pydantic-aliases#aliaschoices) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### serialization\_alias

The serialization alias of the field.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### title

The title of the field.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### field\_title\_generator

A callable that takes a field name and returns title for it.

**Type:** [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), `FieldInfo`], [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### description

The description of the field.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### examples

List of examples of the field.

**Type:** [`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### exclude

Whether to exclude the field from the model serialization.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### exclude\_if

A callable that determines whether to exclude a field during serialization based on its value.

**Type:** [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)], [`bool`](https://docs.python.org/3/builtins/functions.html#bool)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### discriminator

Field name or Discriminator for discriminating the type in a tagged union.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`types.Discriminator`](/guides/pydantic-types#discriminator) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### 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.

**Type:** `Deprecated` | [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### json\_schema\_extra

A dict or callable to provide extra JSON schema properties.

**Type:** `JsonDict` | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[`JsonDict`], [`None`](https://docs.python.org/3/builtins/constants.html#None)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### frozen

Whether the field is frozen.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### validate\_default

Whether to validate the default value of the field.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### repr

Whether to include the field in representation of the model.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool)

#### init

Whether the field should be included in the constructor of the dataclass.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### init\_var

Whether the field should _only_ be included in the constructor of the dataclass, and not stored.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### kw\_only

Whether the field should be a keyword-only argument in the constructor of the dataclass.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### 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`](https://docs.python.org/3/library/typing.html#typing.Annotated) metadata (e.g. [custom types handlers](/guides/concepts-types#as-an-annotation) or any object not recognized by Pydantic).

**Type:** [`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]

#### deprecation\_message

The deprecation message to be emitted, or `None` if not set.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### default\_factory\_takes\_validated\_data

Whether the provided default factory callable has a validated data parameter.

Returns `None` if no default factory is set.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

### Methods

#### \_construct

`@classmethod`

```python
def _construct(cls, metadata: list[Any], **attr_overrides: Any) -> Self
```

Construct the final `FieldInfo` instance, by merging the possibly existing `FieldInfo` instances from the metadata.

With the following example:

```python
class Model(BaseModel):
    f: Annotated[int, Gt(1), Field(description='desc', lt=2)]
```

`metadata` refers to the metadata elements of the `Annotated` form. This metadata is iterated over from left to right:

- If the element is a `Field()` function (which is itself a `FieldInfo` instance), the field attributes (such as `description`) are saved to be set on the final `FieldInfo` instance. On the other hand, some kwargs (such as `lt`) are stored as `metadata` (see `FieldInfo.__init__()`, calling `FieldInfo._collect_metadata()`). In this case, the final metadata list is extended with the one from this instance.
- Else, the element is considered as a single metadata object, and is appended to the final metadata list.

##### Returns

[`Self`](https://docs.python.org/3/library/typing.html#typing.Self) — The final merged `FieldInfo` instance.

##### Parameters

**`metadata`** : [`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]

The list of metadata elements to merge together. If the `FieldInfo` instance to be constructed is for a field with an assigned `Field()`, this `Field()` assignment should be added as the last element of the provided metadata.

**`**attr_overrides`** : [`Any`](https://docs.python.org/3/library/typing.html#typing.Any) _Default:_ `{}`

Extra attributes that should be set on the final merged `FieldInfo` instance.

#### \_from\_dataclass\_field

`@staticmethod`

```python
def _from_dataclass_field(dc_field: DataclassField[Any]) -> FieldInfo
```

Return a new `FieldInfo` instance from a `dataclasses.Field` instance.

##### Returns

`FieldInfo` — The corresponding `FieldInfo` instance.

##### Parameters

**`dc_field`** : `DataclassField`\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]

The `dataclasses.Field` instance to convert.

##### Raises

- `TypeError` — If any of the `FieldInfo` kwargs does not match the `dataclass.Field` kwargs.

#### \_collect\_metadata

`@staticmethod`

```python
def _collect_metadata(kwargs: dict[str, Any]) -> list[Any]
```

Collect annotations from kwargs.

##### Returns

[`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] — A list of metadata objects - a combination of `annotated_types.BaseMetadata` and `PydanticMetadata`.

##### Parameters

**`kwargs`** : [`dict`](https://docs.python.org/3/reference/expressions.html#dict)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]

Keyword arguments passed to the function.

#### get\_default

```python
def get_default(
    *,
    call_default_factory: Literal[True],
    validated_data: dict[str, Any] | None = None,
) -> Any
def get_default(*, call_default_factory: Literal[False] = ...) -> Any
```

Get the default value.

We expose an option for whether to call the default\_factory (if present), as calling it may result in side effects that we want to avoid. However, there are times when it really should be called (namely, when instantiating a model via `model_construct`).

##### Returns

[`Any`](https://docs.python.org/3/library/typing.html#typing.Any) — The default value, calling the default factory if requested or `PydanticUndefined` if not set.

##### Parameters

**`call_default_factory`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) _Default:_ `False`

Whether to call the default factory or not.

**`validated_data`** : [`dict`](https://docs.python.org/3/reference/expressions.html#dict)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

The already validated data to be passed to the default factory.

#### is\_required

```python
def is_required() -> bool
```

Check if the field is required (i.e., does not have a default value or factory).

##### Returns

[`bool`](https://docs.python.org/3/builtins/functions.html#bool) — `True` if the field is required, `False` otherwise.

#### asdict

```python
def asdict() -> _FieldInfoAsDict
```

Return a dictionary representation of the `FieldInfo` instance.

The returned value is a dictionary with three items:

- `annotation`: The type annotation of the field.
- `metadata`: The metadata list.
- `attributes`: A mapping of the remaining `FieldInfo` attributes to their values (e.g. `alias`, `title`).

##### Returns

`_FieldInfoAsDict`

#### \_copy

```python
def _copy() -> Self
```

Return a copy of the `FieldInfo` instance.

##### Returns

[`Self`](https://docs.python.org/3/library/typing.html#typing.Self)

## ModelPrivateAttr

**Bases:** `Representation`

A descriptor for private attributes in class models.

:::callout{intent="warning"}
You generally shouldn’t be creating `ModelPrivateAttr` instances directly, instead use `pydantic.fields.PrivateAttr`. (This is similar to `FieldInfo` vs. `Field`.)
:::

### Attributes

#### default

The default value of the attribute if not provided.

#### 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 validated data (the model’s [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__)) and the already initialized private attributes.

#### default\_factory\_takes\_validated\_data

Whether the provided default factory callable has a validated data parameter.

Returns `None` if no default factory is set.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

### Methods

#### \_\_getattr\_\_

```python
def __getattr__(item: str) -> Any
```

This function improves compatibility with custom descriptors by ensuring delegation happens as expected when the default value of a private attribute is a descriptor.

##### Returns

[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)

#### \_\_set\_name\_\_

```python
def __set_name__(cls: type[Any], name: str) -> None
```

Preserve `__set_name__` protocol defined in https://peps.python.org/pep-0487.

##### Returns

[`None`](https://docs.python.org/3/builtins/constants.html#None)

#### get\_default

```python
def get_default(
    *,
    call_default_factory: Literal[True],
    validated_data: dict[str, Any] | None = None,
) -> Any
def get_default(*, call_default_factory: Literal[False] = ...) -> Any
```

Get the default value.

We expose an option for whether to call the default\_factory (if present), as calling it may result in side effects that we want to avoid. However, there are times when it really should be called (namely, when instantiating a model via `model_construct`).

##### Returns

[`Any`](https://docs.python.org/3/library/typing.html#typing.Any) — The default value, calling the default factory if requested or `None` if not set.

##### Parameters

**`call_default_factory`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) _Default:_ `False`

Whether to call the default factory or not.

**`validated_data`** : [`dict`](https://docs.python.org/3/reference/expressions.html#dict)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

The already validated data to be passed to the default factory.

## ComputedFieldInfo

A container for data from `@computed_field` so that we can access it while building the pydantic-core schema.

### Attributes

#### decorator\_repr

A class variable representing the decorator string, ‘@computed\_field’.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)

#### wrapped\_property

The wrapped computed field property.

**Type:** [`property`](https://docs.python.org/3/builtins/functions.html#property)

#### return\_type

The type of the computed field property’s return value.

**Type:** [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)

#### alias

The alias of the property to be used during serialization.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### alias\_priority

The priority of the alias. This affects whether an alias generator is used.

**Type:** [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### title

Title of the computed field to include in the serialization JSON schema.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### field\_title\_generator

A callable that takes a field name and returns title for it.

**Type:** [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), `ComputedFieldInfo`], [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### description

Description of the computed field to include in the serialization JSON schema.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### 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.

**Type:** `Deprecated` | [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### examples

Example values of the computed field to include in the serialization JSON schema.

**Type:** [`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### json\_schema\_extra

A dict or callable to provide extra JSON schema properties.

**Type:** `JsonDict` | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[`JsonDict`], [`None`](https://docs.python.org/3/builtins/constants.html#None)] | [`None`](https://docs.python.org/3/builtins/constants.html#None)

#### repr

A boolean indicating whether to include the field in the **repr** output.

**Type:** [`bool`](https://docs.python.org/3/builtins/functions.html#bool)

#### deprecation\_message

The deprecation message to be emitted, or `None` if not set.

**Type:** [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None)

### Methods

#### \_update\_from\_config

```python
def _update_from_config(config_wrapper: ConfigWrapper, name: str) -> None
```

Update the instance from the configuration set on the class this computed field belongs to.

##### Returns

[`None`](https://docs.python.org/3/builtins/constants.html#None)

#### \_apply\_alias\_generator

```python
def _apply_alias_generator(
    alias_generator: Callable[[str], str] | AliasGenerator,
    name: str,
) -> None
```

Apply an alias generator to aliases if appropriate.

##### Returns

[`None`](https://docs.python.org/3/builtins/constants.html#None)

##### Parameters

**`alias_generator`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str)], [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)] | [`AliasGenerator`](/guides/pydantic-aliases#aliasgenerator)

A callable that takes a string and returns a string, or an `AliasGenerator` instance.

**`name`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)

The name of the computed field from which to generate the alias.

## Field

```python
def Field(
    default: ellipsis,
    *,
    alias: str | None = _Unset,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = _Unset,
    serialization_alias: str | None = _Unset,
    title: str | None = _Unset,
    field_title_generator: Callable[[str, FieldInfo], str] | None = _Unset,
    description: str | None = _Unset,
    examples: list[Any] | None = _Unset,
    exclude: bool | None = _Unset,
    exclude_if: Callable[[Any], bool] | None = _Unset,
    discriminator: str | types.Discriminator | None = _Unset,
    deprecated: Deprecated | str | bool | None = _Unset,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = _Unset,
    frozen: bool | None = _Unset,
    validate_default: bool | None = _Unset,
    repr: bool = _Unset,
    init: bool | None = _Unset,
    init_var: bool | None = _Unset,
    kw_only: bool | None = _Unset,
    pattern: str | re.Pattern[str] | None = _Unset,
    strict: bool | None = _Unset,
    coerce_numbers_to_str: bool | None = _Unset,
    gt: annotated_types.SupportsGt | None = _Unset,
    ge: annotated_types.SupportsGe | None = _Unset,
    lt: annotated_types.SupportsLt | None = _Unset,
    le: annotated_types.SupportsLe | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    min_length: int | None = _Unset,
    max_length: int | None = _Unset,
    union_mode: Literal['smart', 'left_to_right'] = _Unset,
    fail_fast: bool | None = _Unset,
    **extra: Unpack[_EmptyKwargs],
) -> Any
def Field(
    default: Any,
    *,
    alias: str | None = _Unset,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = _Unset,
    serialization_alias: str | None = _Unset,
    title: str | None = _Unset,
    field_title_generator: Callable[[str, FieldInfo], str] | None = _Unset,
    description: str | None = _Unset,
    examples: list[Any] | None = _Unset,
    exclude: bool | None = _Unset,
    exclude_if: Callable[[Any], bool] | None = _Unset,
    discriminator: str | types.Discriminator | None = _Unset,
    deprecated: Deprecated | str | bool | None = _Unset,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = _Unset,
    frozen: bool | None = _Unset,
    validate_default: Literal[True],
    repr: bool = _Unset,
    init: bool | None = _Unset,
    init_var: bool | None = _Unset,
    kw_only: bool | None = _Unset,
    pattern: str | re.Pattern[str] | None = _Unset,
    strict: bool | None = _Unset,
    coerce_numbers_to_str: bool | None = _Unset,
    gt: annotated_types.SupportsGt | None = _Unset,
    ge: annotated_types.SupportsGe | None = _Unset,
    lt: annotated_types.SupportsLt | None = _Unset,
    le: annotated_types.SupportsLe | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    min_length: int | None = _Unset,
    max_length: int | None = _Unset,
    union_mode: Literal['smart', 'left_to_right'] = _Unset,
    fail_fast: bool | None = _Unset,
    **extra: Unpack[_EmptyKwargs],
) -> Any
def Field(
    default: _T,
    *,
    alias: str | None = _Unset,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = _Unset,
    serialization_alias: str | None = _Unset,
    title: str | None = _Unset,
    field_title_generator: Callable[[str, FieldInfo], str] | None = _Unset,
    description: str | None = _Unset,
    examples: list[Any] | None = _Unset,
    exclude: bool | None = _Unset,
    exclude_if: Callable[[Any], bool] | None = _Unset,
    discriminator: str | types.Discriminator | None = _Unset,
    deprecated: Deprecated | str | bool | None = _Unset,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = _Unset,
    frozen: bool | None = _Unset,
    validate_default: Literal[False] = ...,
    repr: bool = _Unset,
    init: bool | None = _Unset,
    init_var: bool | None = _Unset,
    kw_only: bool | None = _Unset,
    pattern: str | re.Pattern[str] | None = _Unset,
    strict: bool | None = _Unset,
    coerce_numbers_to_str: bool | None = _Unset,
    gt: annotated_types.SupportsGt | None = _Unset,
    ge: annotated_types.SupportsGe | None = _Unset,
    lt: annotated_types.SupportsLt | None = _Unset,
    le: annotated_types.SupportsLe | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    min_length: int | None = _Unset,
    max_length: int | None = _Unset,
    union_mode: Literal['smart', 'left_to_right'] = _Unset,
    fail_fast: bool | None = _Unset,
    **extra: Unpack[_EmptyKwargs],
) -> _T
def Field(
    *,
    default_factory: Callable[[], Any] | Callable[[dict[str, Any]], Any],
    alias: str | None = _Unset,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = _Unset,
    serialization_alias: str | None = _Unset,
    title: str | None = _Unset,
    field_title_generator: Callable[[str, FieldInfo], str] | None = _Unset,
    description: str | None = _Unset,
    examples: list[Any] | None = _Unset,
    exclude: bool | None = _Unset,
    exclude_if: Callable[[Any], bool] | None = _Unset,
    discriminator: str | types.Discriminator | None = _Unset,
    deprecated: Deprecated | str | bool | None = _Unset,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = _Unset,
    frozen: bool | None = _Unset,
    validate_default: Literal[True],
    repr: bool = _Unset,
    init: bool | None = _Unset,
    init_var: bool | None = _Unset,
    kw_only: bool | None = _Unset,
    pattern: str | re.Pattern[str] | None = _Unset,
    strict: bool | None = _Unset,
    coerce_numbers_to_str: bool | None = _Unset,
    gt: annotated_types.SupportsGt | None = _Unset,
    ge: annotated_types.SupportsGe | None = _Unset,
    lt: annotated_types.SupportsLt | None = _Unset,
    le: annotated_types.SupportsLe | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    min_length: int | None = _Unset,
    max_length: int | None = _Unset,
    union_mode: Literal['smart', 'left_to_right'] = _Unset,
    fail_fast: bool | None = _Unset,
    **extra: Unpack[_EmptyKwargs],
) -> Any
def Field(
    *,
    default_factory: Callable[[], _T] | Callable[[dict[str, Any]], _T],
    alias: str | None = _Unset,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = _Unset,
    serialization_alias: str | None = _Unset,
    title: str | None = _Unset,
    field_title_generator: Callable[[str, FieldInfo], str] | None = _Unset,
    description: str | None = _Unset,
    examples: list[Any] | None = _Unset,
    exclude: bool | None = _Unset,
    exclude_if: Callable[[Any], bool] | None = _Unset,
    discriminator: str | types.Discriminator | None = _Unset,
    deprecated: Deprecated | str | bool | None = _Unset,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = _Unset,
    frozen: bool | None = _Unset,
    validate_default: Literal[False] | None = _Unset,
    repr: bool = _Unset,
    init: bool | None = _Unset,
    init_var: bool | None = _Unset,
    kw_only: bool | None = _Unset,
    pattern: str | re.Pattern[str] | None = _Unset,
    strict: bool | None = _Unset,
    coerce_numbers_to_str: bool | None = _Unset,
    gt: annotated_types.SupportsGt | None = _Unset,
    ge: annotated_types.SupportsGe | None = _Unset,
    lt: annotated_types.SupportsLt | None = _Unset,
    le: annotated_types.SupportsLe | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    min_length: int | None = _Unset,
    max_length: int | None = _Unset,
    union_mode: Literal['smart', 'left_to_right'] = _Unset,
    fail_fast: bool | None = _Unset,
    **extra: Unpack[_EmptyKwargs],
) -> _T
def Field(
    *,
    alias: str | None = _Unset,
    alias_priority: int | None = _Unset,
    validation_alias: str | AliasPath | AliasChoices | None = _Unset,
    serialization_alias: str | None = _Unset,
    title: str | None = _Unset,
    field_title_generator: Callable[[str, FieldInfo], str] | None = _Unset,
    description: str | None = _Unset,
    examples: list[Any] | None = _Unset,
    exclude: bool | None = _Unset,
    exclude_if: Callable[[Any], bool] | None = _Unset,
    discriminator: str | types.Discriminator | None = _Unset,
    deprecated: Deprecated | str | bool | None = _Unset,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = _Unset,
    frozen: bool | None = _Unset,
    validate_default: bool | None = _Unset,
    repr: bool = _Unset,
    init: bool | None = _Unset,
    init_var: bool | None = _Unset,
    kw_only: bool | None = _Unset,
    pattern: str | re.Pattern[str] | None = _Unset,
    strict: bool | None = _Unset,
    coerce_numbers_to_str: bool | None = _Unset,
    gt: annotated_types.SupportsGt | None = _Unset,
    ge: annotated_types.SupportsGe | None = _Unset,
    lt: annotated_types.SupportsLt | None = _Unset,
    le: annotated_types.SupportsLe | None = _Unset,
    multiple_of: float | None = _Unset,
    allow_inf_nan: bool | None = _Unset,
    max_digits: int | None = _Unset,
    decimal_places: int | None = _Unset,
    min_length: int | None = _Unset,
    max_length: int | None = _Unset,
    union_mode: Literal['smart', 'left_to_right'] = _Unset,
    fail_fast: bool | None = _Unset,
    **extra: Unpack[_EmptyKwargs],
) -> Any
```

:::callout{intent="note" title="Usage Documentation"}
[Fields](/guides/concepts-fields)
:::

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`.

### Returns

[`Any`](https://docs.python.org/3/library/typing.html#typing.Any) — A new [`FieldInfo`](/guides/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`](https://docs.python.org/3/library/typing.html#typing.Any) _Default:_ `PydanticUndefined`

Default value if the field is not set.

**`default_factory`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[], [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`dict`](https://docs.python.org/3/reference/expressions.html#dict)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]], [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

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`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

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`** : [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Priority of the alias. This affects whether an alias generator is used.

**`validation_alias`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`AliasPath`](/guides/pydantic-aliases#aliaspath) | [`AliasChoices`](/guides/pydantic-aliases#aliaschoices) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Like `alias`, but only affects validation, not serialization.

**`serialization_alias`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Like `alias`, but only affects serialization, not validation.

**`title`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Human-readable title.

**`field_title_generator`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), `FieldInfo`], [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

A callable that takes a field name and returns title for it.

**`description`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Human-readable description.

**`examples`** : [`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Example values for this field.

**`exclude`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Whether to exclude the field from the model serialization.

**`exclude_if`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)], [`bool`](https://docs.python.org/3/builtins/functions.html#bool)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

A callable that determines whether to exclude a field during serialization based on its value.

**`discriminator`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`types.Discriminator`](/guides/pydantic-types#discriminator) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Field name or Discriminator for discriminating the type in a tagged union.

**`deprecated`** : `Deprecated` | [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

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`** : `JsonDict` | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[`JsonDict`], [`None`](https://docs.python.org/3/builtins/constants.html#None)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

A dict or callable to provide extra JSON schema properties.

**`frozen`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Whether the field is frozen. If true, attempts to change the value on an instance will raise an error.

**`validate_default`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

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`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) _Default:_ `_Unset`

A boolean indicating whether to include the field in the `__repr__` output.

**`init`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Whether the field should be included in the constructor of the dataclass. (Only applies to dataclasses.)

**`init_var`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Whether the field should _only_ be included in the constructor of the dataclass. (Only applies to dataclasses.)

**`kw_only`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

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

**`coerce_numbers_to_str`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Whether to enable coercion of any `Number` type to `str` (not applicable in `strict` mode).

**`strict`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

If `True`, strict validation is applied to the field. See [Strict Mode](/guides/concepts-strict-mode) for details.

**`gt`** : `annotated_types.SupportsGt` | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Greater than. If set, value must be greater than this. Only applicable to numbers.

**`ge`** : `annotated_types.SupportsGe` | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Greater than or equal. If set, value must be greater than or equal to this. Only applicable to numbers.

**`lt`** : `annotated_types.SupportsLt` | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Less than. If set, value must be less than this. Only applicable to numbers.

**`le`** : `annotated_types.SupportsLe` | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Less than or equal. If set, value must be less than or equal to this. Only applicable to numbers.

**`multiple_of`** : [`float`](https://docs.python.org/3/builtins/functions.html#float) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Value must be a multiple of this. Only applicable to numbers.

**`min_length`** : [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Minimum length for iterables.

**`max_length`** : [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Maximum length for iterables.

**`pattern`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`re.Pattern`](https://docs.python.org/3/library/re.html#re.Pattern)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Pattern for strings (a regular expression).

**`allow_inf_nan`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Allow `inf`, `-inf`, `nan`. Only applicable to float and [`Decimal`](https://docs.python.org/3/library/decimal.html#decimal.Decimal) numbers.

**`max_digits`** : [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Maximum number of allow digits for strings.

**`decimal_places`** : [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

Maximum number of decimal places allowed for numbers.

**`union_mode`** : [`Literal`](https://docs.python.org/3/library/typing.html#typing.Literal)\[‘smart’, ‘left\_to\_right’] _Default:_ `_Unset`

The strategy to apply when validating a union. Can be `smart` (the default), or `left_to_right`. See [Union Mode](/guides/concepts-unions#union-modes) for details.

**`fail_fast`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `_Unset`

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`** : [`Unpack`](https://docs.python.org/3/library/typing.html#typing.Unpack)\[`_EmptyKwargs`] _Default:_ `{}`

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

:::callout{intent="warning" title="Deprecated"}
The `extra` kwargs is deprecated. Use `json_schema_extra` instead.
:::

## PrivateAttr

```python
def PrivateAttr(default: _T, *, init: Literal[False] = False) -> _T
def PrivateAttr(
    *,
    default_factory: Callable[[], _T] | Callable[[dict[str, Any]], _T],
    init: Literal[False] = False,
) -> _T
def PrivateAttr(*, init: Literal[False] = False) -> Any
```

:::callout{intent="note" title="Usage Documentation"}
[Private Model Attributes](/guides/concepts-models#private-model-attributes)
:::

Indicates that an attribute is intended for private use and not handled during normal validation/serialization.

Private attributes are not validated by Pydantic, so it’s up to you to ensure they are used in a type-safe manner.

Private attributes are stored in `__private_attributes__` on the model.

### Returns

[`Any`](https://docs.python.org/3/library/typing.html#typing.Any) — An instance of [`ModelPrivateAttr`](/guides/pydantic-fields#modelprivateattr) class.

### Parameters

**`default`** : [`Any`](https://docs.python.org/3/library/typing.html#typing.Any) _Default:_ `PydanticUndefined`

The attribute’s default value. Defaults to Undefined.

**`default_factory`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[], [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`dict`](https://docs.python.org/3/reference/expressions.html#dict)\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)]], [`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

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 validated data (the model’s [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__)) and the already initialized private attributes. If both `default` and `default_factory` are set, an error will be raised.

**`init`** : [`Literal`](https://docs.python.org/3/library/typing.html#typing.Literal)\[[`False`](https://docs.python.org/3/builtins/constants.html#False)] _Default:_ `False`

Whether the attribute should be included in the constructor of the dataclass. Always `False`.

### Raises

- `ValueError` — If both `default` and `default_factory` are set.

## computed\_field

```python
def computed_field(func: PropertyT, /) -> PropertyT
def computed_field(
    *,
    alias: str | None = None,
    alias_priority: int | None = None,
    exclude_if: Callable[[Any], bool] | None = None,
    title: str | None = None,
    field_title_generator: Callable[[str, ComputedFieldInfo], str] | None = None,
    description: str | None = None,
    deprecated: Deprecated | str | bool | None = None,
    examples: list[Any] | None = None,
    json_schema_extra: JsonDict | Callable[[JsonDict], None] | None = None,
    repr: bool = True,
    return_type: Any = PydanticUndefined,
) -> Callable[[PropertyT], PropertyT]
```

:::callout{intent="note" title="Usage Documentation"}
[The `computed_field` decorator](/guides/concepts-fields#the-computed_field-decorator)
:::

Decorator to include `property` and `cached_property` when serializing models or dataclasses.

This is useful for fields that are computed from other fields, or for fields that are expensive to compute and should be cached.

```python
from pydantic import BaseModel, computed_field

class Rectangle(BaseModel):
    width: int
    length: int

    @computed_field
    @property
    def area(self) -> int:
        return self.width * self.length

print(Rectangle(width=3, length=2).model_dump())
#> {'width': 3, 'length': 2, 'area': 6}
```

If applied to functions not yet decorated with `@property` or `@cached_property`, the function is automatically wrapped with `property`. Although this is more concise, you will lose IntelliSense in your IDE, and confuse static type checkers, thus explicit use of `@property` is recommended.

:::callout{intent="warning" title="Mypy Warning"}
Even with the `@property` or `@cached_property` applied to your function before `@computed_field`, mypy may throw a `Decorated property not supported` error. See [mypy issue #1362](https://github.com/python/mypy/issues/1362), for more information. To avoid this error message, add `# type: ignore[prop-decorator]` to the `@computed_field` line.

[pyright](https://github.com/microsoft/pyright) supports `@computed_field` without error.
:::

```python
import random

from pydantic import BaseModel, computed_field

class Square(BaseModel):
    width: float

    @computed_field
    def area(self) -> float:  # converted to a `property` by `computed_field`
        return round(self.width**2, 2)

    @area.setter
    def area(self, new_area: float) -> None:
        self.width = new_area**0.5

    @computed_field(alias='the magic number', repr=False)
    def random_number(self) -> int:
        return random.randint(0, 1_000)

square = Square(width=1.3)

# `random_number` does not appear in representation
print(repr(square))
#> Square(width=1.3, area=1.69)

print(square.random_number)
#> 3

square.area = 4

print(square.model_dump_json(by_alias=True))
#> {"width":2.0,"area":4.0,"the magic number":3}
```

:::callout{intent="warning" title="Overriding with computed_field"}
You can’t override a field from a parent class with a `computed_field` in the child class. `mypy` complains about this behavior if allowed, and `dataclasses` doesn’t allow this pattern either. See the example below:
:::

```python
from pydantic import BaseModel, computed_field

class Parent(BaseModel):
    a: str

try:

    class Child(Parent):
        @computed_field
        @property
        def a(self) -> str:
            return 'new a'

except TypeError as e:
    print(e)
    '''
    Field 'a' of class 'Child' overrides symbol of same name in a parent class. This override with a computed_field is incompatible.
    '''
```

Private properties decorated with `@computed_field` have `repr=False` by default.

```python
from functools import cached_property

from pydantic import BaseModel, computed_field

class Model(BaseModel):
    foo: int

    @computed_field
    @cached_property
    def _private_cached_property(self) -> int:
        return -self.foo

    @computed_field
    @property
    def _private_property(self) -> int:
        return -self.foo

m = Model(foo=1)
print(repr(m))
#> Model(foo=1)
```

### Returns

`PropertyT` | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[`PropertyT`], `PropertyT`] — A proxy wrapper for the property.

### Parameters

**`func`** : `PropertyT` | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

the function to wrap.

**`alias`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

alias to use when serializing this computed field, only used when `by_alias=True`

**`alias_priority`** : [`int`](https://docs.python.org/3/builtins/functions.html#int) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

priority of the alias. This affects whether an alias generator is used

**`exclude_if`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)], [`bool`](https://docs.python.org/3/builtins/functions.html#bool)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

A callable that determines whether to exclude this computed field during serialization based on its value.

**`title`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

Title to use when including this computed field in JSON Schema

**`field_title_generator`** : [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[[`str`](https://docs.python.org/3/builtins/stdtypes.html#str), `ComputedFieldInfo`], [`str`](https://docs.python.org/3/builtins/stdtypes.html#str)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

A callable that takes a field name and returns title for it.

**`description`** : [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

Description to use when including this computed field in JSON Schema, defaults to the function’s docstring

**`deprecated`** : `Deprecated` | [`str`](https://docs.python.org/3/builtins/stdtypes.html#str) | [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

A deprecation message (or an instance of `warnings.deprecated` or the `typing_extensions.deprecated` backport). to be emitted when accessing the field. Or a boolean. This will automatically be set if the property is decorated with the `deprecated` decorator.

**`examples`** : [`list`](https://docs.python.org/3/glossary.html#term-list)\[[`Any`](https://docs.python.org/3/library/typing.html#typing.Any)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

Example values to use when including this computed field in JSON Schema

**`json_schema_extra`** : `JsonDict` | [`Callable`](https://docs.python.org/3/library/typing.html#typing.Callable)\[\[`JsonDict`], [`None`](https://docs.python.org/3/builtins/constants.html#None)] | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

A dict or callable to provide extra JSON schema properties.

**`repr`** : [`bool`](https://docs.python.org/3/builtins/functions.html#bool) | [`None`](https://docs.python.org/3/builtins/constants.html#None) _Default:_ `None`

whether to include this computed field in model repr. Default is `False` for private properties and `True` for public properties.

**`return_type`** : [`Any`](https://docs.python.org/3/library/typing.html#typing.Any) _Default:_ `PydanticUndefined`

optional return for serialization logic to expect when serializing to JSON, if included this must be correct, otherwise a `TypeError` is raised. If you don’t include a return type Any is used, which does runtime introspection to handle arbitrary objects.

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## Related pages

- [API Documentation](./api-documentation-index.md)
- [Concepts](./concepts-index.md)
- [Dev Tools](./dev-tools-index.md)
- [Error Messages](./error-messages-index.md)
- [Examples](./examples-index.md)
- [Integrations](./integrations-index.md)
- [Internals](./internals-index.md)
- [Production Tools](./production-tools-index.md)
- [Pydantic](./pydantic-index.md)
- [Pydantic Core](./pydantic-core-index.md)

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