How can I implement custom validation in Pydantic?

How can I implement custom validation in Pydantic?

You can implement custom validation in Pydantic by using the @validator decorator. This allows you to define custom validation logic for your model fields.

Can you show me an example of using the @validator decorator?

Sure! Here's a simple example:

from pydantic import BaseModel, validator

class User(BaseModel):
    username: str
    age: int

    @validator('age')
    def check_age(cls, v):
        if v < 0:
            raise ValueError('Age must be a positive integer')
        return v

What happens if the validation fails?

If the validation fails, Pydantic will raise a ValidationError, and you can catch this exception to handle it appropriately.

Can I use multiple validators for a single field?

Yes, you can use multiple validators for a single field by applying the @validator decorator multiple times, or by combining validation logic within a single validator.