Overview

Pydantic 2.8, released on August 2, 2024, adds validation warnings and improves tagged unions.

Main Features

Warnings and tagged unions

Validation warnings report non-blocking issues. Tagged unions benefit from clearer syntax.

python 
from pydantic import BaseModel, Field
from typing import Literal, Union, Annotated

class Cat(BaseModel):
    type: Literal['cat'] = 'cat'
    meows: bool = True

class Dog(BaseModel):
    type: Literal['dog'] = 'dog'
    barks: bool = True

Animal = Annotated[
    Union[Cat, Dog],
    Field(discriminator='type'),
]

class Household(BaseModel):
    animal: Animal

h = Household(animal={'type': 'cat', 'meows': True})
print(h.animal)  # type='cat' meows=True

Sources