TypeAdapter

You may have types that are not BaseModels that you want to validate data against. Or you may want to validate a List[SomeModel], or dump it to JSON.

For use cases like this, Pydantic provides TypeAdapter, which can be used for type validation, serialization, and JSON schema generation without creating a BaseModel.

A TypeAdapter instance exposes some of the functionality from BaseModel instance methods for types that do not have such methods (such as dataclasses, primitive types, and more):

from typing import List

from typing_extensions import TypedDict

from pydantic import TypeAdapter, ValidationError

class User(TypedDict):
    name: str
    id: int

UserListValidator = TypeAdapter(List[User])
print(repr(UserListValidator.validate_python([{'name': 'Fred', 'id': '3'}])))
#> [{'name': 'Fred', 'id': 3}]

try:
    UserListValidator.validate_python(
        [{'name': 'Fred', 'id': 'wrong', 'other': 'no'}]
    )
except ValidationError as e:
    print(e)
    '''
    1 validation error for list[typed-dict]
    0.id
      Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='wrong', input_type=str]
    '''

Note

Despite some overlap in use cases with RootModel, TypeAdapter should not be used as a type annotation for specifying fields of a BaseModel, etc.

Parsing data into a specified type

TypeAdapter can be used to apply the parsing logic to populate Pydantic models in a more ad-hoc way. This function behaves similarly to BaseModel.model_validate, but works with arbitrary Pydantic-compatible types.

This is especially useful when you want to parse results into a type that is not a direct subclass of BaseModel. For example:

from typing import List

from pydantic import BaseModel, TypeAdapter

class Item(BaseModel):
    id: int
    name: str

# `item_data` could come from an API call, eg., via something like:
# item_data = requests.get('https://my-api.com/items').json()
item_data = [{'id': 1, 'name': 'My Item'}]

items = TypeAdapter(List[Item]).validate_python(item_data)
print(items)
#> [Item(id=1, name='My Item')]

TypeAdapter is capable of parsing data into any of the types Pydantic can handle as fields of a BaseModel.

TypeAdapter

TypeAdapter(type, *, config=None, _parent_depth=2)

Bases: Generic[T]

Type adapters provide a flexible way to perform validation and serialization based on a Python type.

A TypeAdapter instance exposes some of the functionality from BaseModel instance methods for types that do not have such methods (such as dataclasses, primitive types, and more).

Note that TypeAdapter is not an actual type, so you cannot use it in type annotations.

Attributes:

Name	Type	Description
core_schema		The core schema for the type.
validator	SchemaValidator	The schema validator for the type.
serializer		The schema serializer for the type.

Source code in pydantic/type_adapter.py

def __init__(self, type: Any, *, config: ConfigDict | None = None, _parent_depth: int = 2) -> None:
    """Initializes the TypeAdapter object."""
    config_wrapper = _config.ConfigWrapper(config)

    try:
        type_has_config = issubclass(type, BaseModel) or is_dataclass(type) or is_typeddict(type)
    except TypeError:
        # type is not a class
        type_has_config = False

    if type_has_config and config is not None:
        raise PydanticUserError(
            'Cannot use `config` when the type is a BaseModel, dataclass or TypedDict.'
            ' These types can have their own config and setting the config via the `config`'
            ' parameter to TypeAdapter will not override it, thus the `config` you passed to'
            ' TypeAdapter becomes meaningless, which is probably not what you want.',
            code='type-adapter-config-unused',
        )

    core_schema: CoreSchema
    try:
        core_schema = _getattr_no_parents(type, '__pydantic_core_schema__')
    except AttributeError:
        core_schema = _get_schema(type, config_wrapper, parent_depth=_parent_depth + 1)

    core_schema = _discriminated_union.apply_discriminators(_core_utils.simplify_schema_references(core_schema))

    core_schema = _core_utils.validate_core_schema(core_schema)

    core_config = config_wrapper.core_config(None)
    validator: SchemaValidator
    try:
        validator = _getattr_no_parents(type, '__pydantic_validator__')
    except AttributeError:
        validator = create_schema_validator(core_schema, core_config, config_wrapper.plugin_settings)

    serializer: SchemaSerializer
    try:
        serializer = _getattr_no_parents(type, '__pydantic_serializer__')
    except AttributeError:
        serializer = SchemaSerializer(core_schema, core_config)

    self.core_schema = core_schema
    self.validator = validator
    self.serializer = serializer

validate_python

validate_python(
    __object,
    *,
    strict=None,
    from_attributes=None,
    context=None
)

Validate a Python object against the model.

Parameters:

Name	Type	Description	Default
__object	Any	The Python object to validate against the model.	required
strict	bool | None	Whether to strictly check types.	None
from_attributes	bool | None	Whether to extract data from object attributes.	None
context	dict[str, Any] | None	Additional context to pass to the validator.	None

Returns:

Type	Description
T	The validated object.

Source code in pydantic/type_adapter.py

def validate_python(
    self,
    __object: Any,
    *,
    strict: bool | None = None,
    from_attributes: bool | None = None,
    context: dict[str, Any] | None = None,
) -> T:
    """Validate a Python object against the model.

    Args:
        __object: The Python object to validate against the model.
        strict: Whether to strictly check types.
        from_attributes: Whether to extract data from object attributes.
        context: Additional context to pass to the validator.

    Returns:
        The validated object.
    """
    return self.validator.validate_python(__object, strict=strict, from_attributes=from_attributes, context=context)

validate_json

validate_json(__data, *, strict=None, context=None)

Validate a JSON string or bytes against the model.

Parameters:

Name	Type	Description	Default
__data	str | bytes	The JSON data to validate against the model.	required
strict	bool | None	Whether to strictly check types.	None
context	dict[str, Any] | None	Additional context to use during validation.	None

Returns:

Type	Description
T	The validated object.

Source code in pydantic/type_adapter.py

def validate_json(
    self, __data: str | bytes, *, strict: bool | None = None, context: dict[str, Any] | None = None
) -> T:
    """Validate a JSON string or bytes against the model.

    Args:
        __data: The JSON data to validate against the model.
        strict: Whether to strictly check types.
        context: Additional context to use during validation.

    Returns:
        The validated object.
    """
    return self.validator.validate_json(__data, strict=strict, context=context)

validate_strings

validate_strings(__obj, *, strict=None, context=None)

Validate object contains string data against the model.

Parameters:

Name	Type	Description	Default
__obj	Any	The object contains string data to validate.	required
strict	bool | None	Whether to strictly check types.	None
context	dict[str, Any] | None	Additional context to use during validation.	None

Returns:

Type	Description
T	The validated object.

Source code in pydantic/type_adapter.py

def validate_strings(self, __obj: Any, *, strict: bool | None = None, context: dict[str, Any] | None = None) -> T:
    """Validate object contains string data against the model.

    Args:
        __obj: The object contains string data to validate.
        strict: Whether to strictly check types.
        context: Additional context to use during validation.

    Returns:
        The validated object.
    """
    return self.validator.validate_strings(__obj, strict=strict, context=context)

get_default_value

get_default_value(*, strict=None, context=None)

Get the default value for the wrapped type.

Parameters:

Name	Type	Description	Default
strict	bool | None	Whether to strictly check types.	None
context	dict[str, Any] | None	Additional context to pass to the validator.	None

Returns:

Type	Description
Some[T] | None	The default value wrapped in a Some if there is one or None if not.

Source code in pydantic/type_adapter.py

def get_default_value(self, *, strict: bool | None = None, context: dict[str, Any] | None = None) -> Some[T] | None:
    """Get the default value for the wrapped type.

    Args:
        strict: Whether to strictly check types.
        context: Additional context to pass to the validator.

    Returns:
        The default value wrapped in a `Some` if there is one or None if not.
    """
    return self.validator.get_default_value(strict=strict, context=context)

dump_python

dump_python(
    __instance,
    *,
    mode="python",
    include=None,
    exclude=None,
    by_alias=False,
    exclude_unset=False,
    exclude_defaults=False,
    exclude_none=False,
    round_trip=False,
    warnings=True
)

Dump an instance of the adapted type to a Python object.

Parameters:

Name	Type	Description	Default
__instance	T	The Python object to serialize.	required
mode	Literal['json', 'python']	The output format.	'python'
include	IncEx | None	Fields to include in the output.	None
exclude	IncEx | None	Fields to exclude from the output.	None
by_alias	bool	Whether to use alias names for field names.	False
exclude_unset	bool	Whether to exclude unset fields.	False
exclude_defaults	bool	Whether to exclude fields with default values.	False
exclude_none	bool	Whether to exclude fields with None values.	False
round_trip	bool	Whether to output the serialized data in a way that is compatible with deserialization.	False
warnings	bool	Whether to display serialization warnings.	True

Returns:

Type	Description
Any	The serialized object.

Source code in pydantic/type_adapter.py

def dump_python(
    self,
    __instance: T,
    *,
    mode: Literal['json', 'python'] = 'python',
    include: IncEx | None = None,
    exclude: IncEx | None = None,
    by_alias: bool = False,
    exclude_unset: bool = False,
    exclude_defaults: bool = False,
    exclude_none: bool = False,
    round_trip: bool = False,
    warnings: bool = True,
) -> Any:
    """Dump an instance of the adapted type to a Python object.

    Args:
        __instance: The Python object to serialize.
        mode: The output format.
        include: Fields to include in the output.
        exclude: Fields to exclude from the output.
        by_alias: Whether to use alias names for field names.
        exclude_unset: Whether to exclude unset fields.
        exclude_defaults: Whether to exclude fields with default values.
        exclude_none: Whether to exclude fields with None values.
        round_trip: Whether to output the serialized data in a way that is compatible with deserialization.
        warnings: Whether to display serialization warnings.

    Returns:
        The serialized object.
    """
    return self.serializer.to_python(
        __instance,
        mode=mode,
        by_alias=by_alias,
        include=include,
        exclude=exclude,
        exclude_unset=exclude_unset,
        exclude_defaults=exclude_defaults,
        exclude_none=exclude_none,
        round_trip=round_trip,
        warnings=warnings,
    )

dump_json

dump_json(
    __instance,
    *,
    indent=None,
    include=None,
    exclude=None,
    by_alias=False,
    exclude_unset=False,
    exclude_defaults=False,
    exclude_none=False,
    round_trip=False,
    warnings=True
)

Serialize an instance of the adapted type to JSON.

Parameters:

Name	Type	Description	Default
__instance	T	The instance to be serialized.	required
indent	int | None	Number of spaces for JSON indentation.	None
include	IncEx | None	Fields to include.	None
exclude	IncEx | None	Fields to exclude.	None
by_alias	bool	Whether to use alias names for field names.	False
exclude_unset	bool	Whether to exclude unset fields.	False
exclude_defaults	bool	Whether to exclude fields with default values.	False
exclude_none	bool	Whether to exclude fields with a value of None.	False
round_trip	bool	Whether to serialize and deserialize the instance to ensure round-tripping.	False
warnings	bool	Whether to emit serialization warnings.	True

Returns:

Type	Description
bytes	The JSON representation of the given instance as bytes.

Source code in pydantic/type_adapter.py

def dump_json(
    self,
    __instance: T,
    *,
    indent: int | None = None,
    include: IncEx | None = None,
    exclude: IncEx | None = None,
    by_alias: bool = False,
    exclude_unset: bool = False,
    exclude_defaults: bool = False,
    exclude_none: bool = False,
    round_trip: bool = False,
    warnings: bool = True,
) -> bytes:
    """Serialize an instance of the adapted type to JSON.

    Args:
        __instance: The instance to be serialized.
        indent: Number of spaces for JSON indentation.
        include: Fields to include.
        exclude: Fields to exclude.
        by_alias: Whether to use alias names for field names.
        exclude_unset: Whether to exclude unset fields.
        exclude_defaults: Whether to exclude fields with default values.
        exclude_none: Whether to exclude fields with a value of `None`.
        round_trip: Whether to serialize and deserialize the instance to ensure round-tripping.
        warnings: Whether to emit serialization warnings.

    Returns:
        The JSON representation of the given instance as bytes.
    """
    return self.serializer.to_json(
        __instance,
        indent=indent,
        include=include,
        exclude=exclude,
        by_alias=by_alias,
        exclude_unset=exclude_unset,
        exclude_defaults=exclude_defaults,
        exclude_none=exclude_none,
        round_trip=round_trip,
        warnings=warnings,
    )

json_schema

json_schema(
    *,
    by_alias=True,
    ref_template=DEFAULT_REF_TEMPLATE,
    schema_generator=GenerateJsonSchema,
    mode="validation"
)

Generate a JSON schema for the adapted type.

Parameters:

Name	Type	Description	Default
by_alias	bool	Whether to use alias names for field names.	True
ref_template	str	The format string used for generating $ref strings.	DEFAULT_REF_TEMPLATE
schema_generator	type[GenerateJsonSchema]	The generator class used for creating the schema.	GenerateJsonSchema
mode	JsonSchemaMode	The mode to use for schema generation.	'validation'

Returns:

Type	Description
dict[str, Any]	The JSON schema for the model as a dictionary.

Source code in pydantic/type_adapter.py

def json_schema(
    self,
    *,
    by_alias: bool = True,
    ref_template: str = DEFAULT_REF_TEMPLATE,
    schema_generator: type[GenerateJsonSchema] = GenerateJsonSchema,
    mode: JsonSchemaMode = 'validation',
) -> dict[str, Any]:
    """Generate a JSON schema for the adapted type.

    Args:
        by_alias: Whether to use alias names for field names.
        ref_template: The format string used for generating $ref strings.
        schema_generator: The generator class used for creating the schema.
        mode: The mode to use for schema generation.

    Returns:
        The JSON schema for the model as a dictionary.
    """
    schema_generator_instance = schema_generator(by_alias=by_alias, ref_template=ref_template)
    return schema_generator_instance.generate(self.core_schema, mode=mode)

json_schemas staticmethod

json_schemas(
    __inputs,
    *,
    by_alias=True,
    title=None,
    description=None,
    ref_template=DEFAULT_REF_TEMPLATE,
    schema_generator=GenerateJsonSchema
)

Generate a JSON schema including definitions from multiple type adapters.

Parameters:

Name	Type	Description	Default
__inputs	Iterable[tuple[JsonSchemaKeyT, JsonSchemaMode, TypeAdapter[Any]]]	Inputs to schema generation. The first two items will form the keys of the (first) output mapping; the type adapters will provide the core schemas that get converted into definitions in the output JSON schema.	required
by_alias	bool	Whether to use alias names.	True
title	str | None	The title for the schema.	None
description	str | None	The description for the schema.	None
ref_template	str	The format string used for generating $ref strings.	DEFAULT_REF_TEMPLATE
schema_generator	type[GenerateJsonSchema]	The generator class used for creating the schema.	GenerateJsonSchema

Returns:

Type

Description

tuple[dict[tuple[JsonSchemaKeyT, JsonSchemaMode], JsonSchemaValue], JsonSchemaValue]

A tuple where: The first element is a dictionary whose keys are tuples of JSON schema key type and JSON mode, and whose values are the JSON schema corresponding to that pair of inputs. (These schemas may have JsonRef references to definitions that are defined in the second returned element.) The second element is a JSON schema containing all definitions referenced in the first returned element, along with the optional title and description keys.

Source code in pydantic/type_adapter.py

@staticmethod
def json_schemas(
    __inputs: Iterable[tuple[JsonSchemaKeyT, JsonSchemaMode, TypeAdapter[Any]]],
    *,
    by_alias: bool = True,
    title: str | None = None,
    description: str | None = None,
    ref_template: str = DEFAULT_REF_TEMPLATE,
    schema_generator: type[GenerateJsonSchema] = GenerateJsonSchema,
) -> tuple[dict[tuple[JsonSchemaKeyT, JsonSchemaMode], JsonSchemaValue], JsonSchemaValue]:
    """Generate a JSON schema including definitions from multiple type adapters.

    Args:
        __inputs: Inputs to schema generation. The first two items will form the keys of the (first)
            output mapping; the type adapters will provide the core schemas that get converted into
            definitions in the output JSON schema.
        by_alias: Whether to use alias names.
        title: The title for the schema.
        description: The description for the schema.
        ref_template: The format string used for generating $ref strings.
        schema_generator: The generator class used for creating the schema.

    Returns:
        A tuple where:

            - The first element is a dictionary whose keys are tuples of JSON schema key type and JSON mode, and
                whose values are the JSON schema corresponding to that pair of inputs. (These schemas may have
                JsonRef references to definitions that are defined in the second returned element.)
            - The second element is a JSON schema containing all definitions referenced in the first returned
                element, along with the optional title and description keys.

    """
    schema_generator_instance = schema_generator(by_alias=by_alias, ref_template=ref_template)

    inputs = [(key, mode, adapter.core_schema) for key, mode, adapter in __inputs]

    json_schemas_map, definitions = schema_generator_instance.generate_definitions(inputs)

    json_schema: dict[str, Any] = {}
    if definitions:
        json_schema['$defs'] = definitions
    if title:
        json_schema['title'] = title
    if description:
        json_schema['description'] = description

    return json_schemas_map, json_schema