Type Adapter

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.

API Documentation

pydantic.type_adapter.TypeAdapter

For use cases like this, Pydantic provides TypeAdapter, which can be used for type validation, serialization, and JSON schema generation without needing to create 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


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

try:
    UserListAdapter.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.

Performance considerations

When creating an instance of TypeAdapter, the provided type must be analyzed and converted into a pydantic-core schema. This comes with some non-trivial overhead, so it is recommended to create a TypeAdapter for a given type just once and reuse it in loops or other performance-critical code.