Pydantic 库 validator 中 per 参数的执行顺序问题：为什么将 per 设置为 True 后，验证方法的执行顺序并非第一位？

from pydantic import BaseModel, ValidationError, validator

class UserModel(BaseModel):
    name: str
    username: str
    password1:str
    password2: str

    @validator('name')
    def name_must_contain_space(cls, v,values):
        print(values,'name')
        if ' ' not in v:
            raise ValueError('must contain a space')
        return v.title()

    @validator('password2')
    def passwords_match(cls, v, values):
        print(values,'password2')
        if 'password1' in values and v != values['password1']:
            raise ValueError('passwords do not match')
        return v

    @validator('username',pre=True)
    def username_alphanumeric(cls, v,values):
        print(values,'执行顺序优先')
        assert v.isalnum(), 'must be alphanumeric'
        return v

user = UserModel(
    name='samuel colvin',
    username='scolvin',
    password1='zxcvbn',
    password2='zxcvbn',
)