How do I use Pydantic for data validation in Python?

How do I use Pydantic for data validation in Python?

Pydantic is a data validation and settings management library for Python. You can define data models using Python type annotations.

Can you show me a simple example?

Sure! Here's a basic example:

from pydantic import BaseModel

class User(BaseModel):
    id: int
    name: str
    email: str

user = User(id=1, name='John Doe', email='[email protected]')
print(user)

What happens if I provide invalid data?

If you provide invalid data, Pydantic will raise a ValidationError. For example:

user = User(id='not-an-int', name='John Doe', email='[email protected]')

This will raise an error because 'id' must be an integer.

Can I add custom validation?

Yes! You can add custom validation methods using the @validator decorator. Here's an example:

from pydantic import BaseModel, validator

class User(BaseModel):
    name: str

    @validator('name')
    def name_must_not_be_empty(cls, v):
        if not v:
            raise ValueError('Name must not be empty')
        return v