What is Pydantic and how does it integrate with FastAPI?

Pydantic is a data validation library that uses Python type hints to validate data. In FastAPI:

• Request Validation: Automatically validates incoming request data
• Response Serialization: Converts Python objects to JSON
• Documentation: Generates JSON Schema for API docs
• Error Handling: Provides detailed validation error messages

from pydantic import BaseModel, validator
from typing import Optional

class User(BaseModel):
    name: str
    email: str
    age: Optional[int] = None
    
    @validator('email')
    def validate_email(cls, v):
        if '@' not in v:
            raise ValueError('Invalid email')
        return v