How to reuse validators on Pydantic V2

Pydantic is a data validation and settings management library for Python. It is especially useful for data validation in web applications and APIs. With the release of Pydantic V2, reusing validators has become even more convenient and flexible.

Defining validators in Pydantic V2

Validators in Pydantic V2 are defined using the @validator decorator, which allows you to define custom validation logic for a particular field in a Pydantic model.

Reusing validators

In Pydantic V2, you can reuse validators by defining them as standalone functions and then applying them to multiple fields in different models. This allows you to maintain a single source of truth for your validation logic and easily apply it across your application.

Example

Let’s say you have a validator for email address validation:

    from pydantic import BaseModel, validator

    def validate_email(email):
        if "@" not in email:
            raise ValueError("Invalid email address")
        return email

    class User(BaseModel):
        email: str

        @validator("email")
        def validate_email(cls, v):
            return validate_email(v)
    

Now, if you want to reuse the validate_email validator in another model, you can simply import the function and apply it using the @validator decorator:

    from pydantic import BaseModel, validator
    from my_module import validate_email

    class AnotherModel(BaseModel):
        email: str

        @validator("email")
        def validate_email(cls, v):
            return validate_email(v)
    

Conclusion

By defining validators as standalone functions and reusing them across different Pydantic models, you can improve code reusability and maintainability in your application. Pydantic V2 provides a powerful and flexible way to handle data validation, making it easier to write clean and organized code.