from uuid import UUID, uuid4 from pydantic import BaseModel, Field, field_validator class Account(BaseModel): id: UUID = Field(default_factory=uuid4) name: str = "" currency: str = "USD" balance: float = 0.0 @field_validator("balance") @classmethod def _balance_non_negative(cls, v: float) -> float: if v < 0: raise ValueError("balance must be non-negative") return v