Overview

Pydantic 1.8, released on March 28, 2021, introduces custom JSON encoders and strengthens strict types for finer validation.

Main Features

Custom JSON encoders

The json_encoders configuration lets you define how custom types are serialized to JSON, avoiding serialization errors for non-standard types.

python 
from datetime import datetime
from pydantic import BaseModel

class Event(BaseModel):
    name: str
    date: datetime
    attendees: set[str]

    class Config:
        json_encoders = {
            datetime: lambda v: v.strftime('%Y-%m-%d %H:%M'),
            set: list,
        }

evt = Event(name='PyCon', date=datetime(2021, 5, 14), attendees={'Alice', 'Bob'})
print(evt.json())  # {"name": "PyCon", "date": "2021-05-14 00:00", ...}

Strict types

Strict types like StrictStr, StrictInt, and StrictBool reject implicit conversions, ensuring received data matches the expected type exactly.

python 
from pydantic import BaseModel, StrictInt, StrictStr, ValidationError

class Config(BaseModel):
    port: StrictInt
    host: StrictStr

# OK: exact types
c = Config(port=8080, host='localhost')

# Error: '8080' is a string, not an int
try:
    Config(port='8080', host='localhost')
except ValidationError as e:
    print(e)  # value is not a valid integer

Sources