from pydantic import BaseModel, field_validator from pydantic_swift_code import SwiftCode class BankAccount(BaseModel): ... swift_code: SwiftCode @field_validator("swift_code", mode="after") @classmethod def validate_swift_code_after_init(cls, swift_code: str) -> str: """Custom validation""" if swift_code[:4] not in {"REVO", "MONZ"}: raise ValueError("Only Revolut and Monzo swift codes are allowed") if swift_code[4:6] not in {"US", "GB"}: raise ValueError("Only GB and US swift codes are allowed") return swift_code