Pydantic Field Validator Coercion

from typing import Annotated

from pydantic import BaseModel, Field, field_validator, model_validator


class SignupForm(BaseModel):
    email: Annotated[str, Field(min_length=5, max_length=120)]
    age: Annotated[int, Field(ge=18, le=120)]
    zipcode: str
    password: str
    password_confirm: str

    @field_validator('email', mode='before')
    @classmethod
    def normalize_email(cls, raw: object) -> object:
        if isinstance(raw, str):
            candidate = raw.strip().lower()
            if candidate.startswith('mailto:'):
                candidate = candidate.removeprefix('mailto:')
            return candidate
        return raw

    @field_validator('zipcode', mode='before')
    @classmethod
    def digits_only(cls, raw: object) -> object:
        if isinstance(raw, str) and raw.isdigit() and len(raw) == 5:
            return raw
        raise ValueError('zipcode must be exactly 5 digits')

    @model_validator(mode='after')
    def passwords_match(self) -> 'SignupForm':
        if self.password != self.password_confirm:
            raise ValueError('passwords do not match')
        return self


form = SignupForm(
    email='  MAILTO:[email protected] ',
    age='30',
    zipcode='02138',
    password='hunter2xx',
    password_confirm='hunter2xx',
)
print('normalized email:', form.email, 'age type:', type(form.age).__name__)