为什么 __set_name__ 不会为 StringField/flask_wtf 调用

Question

任何人都知道为什么没有为 StringField/flask_wtf 类调用钩子 set_name（由装饰函数添加）。虽然它被称为“简单构造”的类？如下代码所示：

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, BooleanField, SubmitField, SelectField, IntegerField
from wtforms.validators import DataRequired, Email, ValidationError, StopValidation
from flask import Flask, render_template, flash, redirect, url_for, request, jsonify, session

def AddSetName(Cl) :
    class ClsWithSetName(Cl):
        def __set_name__(self, owner, name):
            print("Set Name ", self, owner, name,super(Cl,self))
#            super(Cl,self).__set_name__(self,owner,name)
            self.key = name
            try:
                owner.KeyFields.append(name)
            except :
                owner.KeyFields = [name]

    return ClsWithSetName

class Trait(object):
    def __init__(self, minimum, maximum):
        self.minimum = minimum
        self.maximum = maximum

    def __get__(self, instance, owner):
        print("get called ", self, instance, owner)
        return instance.__dict__[self.key]

    def __set__(self, instance, value):
        print("Set called ", self, instance, value)
        if self.minimum < value < self.maximum:
            instance.__dict__[self.key] = value
        else:
            raise ValueError("value not in range")

Trait = AddSetName(Trait)
StringField = AddSetName(StringField)

class T1:
    Val1=Trait(0,10)
    Val2=Trait(0,5)

class FrmLogin(FlaskForm):
    username=StringField('username', validators=[DataRequired])
    password=StringField('password', validators=[DataRequired])

if __name__ == '__main__':
    pass
    print(dir(StringField))
#    x = T1()
#    x.Val1 = 8
#    x.Val2 = 4
#    print(x)
#    print(T1.KeyFields)

>>> Set Name  <__main__.AddSetName.<locals>.ClsWithSetName object at 0x0000018E2A0FDD88> <class '__main__.T1'> Val1 <super: <class 'Trait'>, <ClsWithSetName object>>
>>>Set Name  <__main__.AddSetName.<locals>.ClsWithSetName object at 0x0000018E2A0FDE08> <class '__main__.T1'> Val2 <super: <class 'Trait'>, <ClsWithSetName object>>
>>>['__call__', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__html__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__unicode__', '__weakref__', '_formfield', '_run_validation_chain', '_translations', '_value', 'do_not_call_in_templates', 'errors', 'gettext', 'ngettext', 'populate_obj', 'post_validate', 'pre_validate', 'process', 'process_data', 'process_errors', 'process_formdata', 'raw_data', 'validate', 'validators', 'widget']

输出没有显示对 StringField 的 set_name 的任何调用！

有什么“重新激活”或模仿这个电话的建议吗？

Answer 1

有一种情况可能导致类的“未调用 set_name”：当类包含不返回实例的 new 定义时（按预期返回对象的 None)。如果没有实例，python 不会调用该类的 init 和 set_name。

我尝试使用 StringField 组件来检查这个案例：

from flask_wtf import FlaskForm
from wtforms import StringField
from wtforms.validators import DataRequired
from flask import Flask


app = Flask(__name__ )

@app.route('/', methods=['GET', 'POST'])
def MainPage():
    Frm = FrmLogin()


def AddSetName(Cl) :
    class ClsWithSetName(Cl):
        def __new__(cls, *args, **Kargs):
            if len(Kargs) == 0 :
                inst = super(ClsWithSetName, cls).__new__(cls)
            else:
                inst = super(ClsWithSetName, cls).__new__(cls, *args, **Kargs)
            print("new ", inst)
            return inst

        def __init__(self, *args, **Kargs):
            super(ClsWithSetName, self).__init__(*args, **Kargs)
            print("init get called")

        def __set_name__(self, owner, name):
            print("Set Name ", self, owner, name,super(Cl,self))
#            super(Cl,self).__set_name__(self,owner,name)
            self.key = name
            try:
                owner.KeyFields.append(name)
            except :
                owner.KeyFields = [name]

    return ClsWithSetName

class Trait(object):
    def __init__(self, minimum, maximum):
        self.minimum = minimum
        self.maximum = maximum

    def __get__(self, instance, owner):
        print("get called ", self, instance, owner)
        return instance.__dict__[self.key]

    def __set__(self, instance, value):
        print("Set called ", self, instance, value)
        if self.minimum < value < self.maximum:
            instance.__dict__[self.key] = value
        else:
            raise ValueError("value not in range")

Trait = AddSetName(Trait)
StringField = AddSetName(StringField)

class T1:
    Val1=Trait(0,10)
#    Val2=Trait(0,5)
    pass

class FrmLogin(FlaskForm):
    username=StringField('username', validators=[DataRequired])
#    password=StringField('password', validators=[DataRequired])
    pass

if __name__ == '__main__':
    pass

>>> new  <__main__.AddSetName.<locals>.ClsWithSetName object at 0x0000017F46386348>
>>> init get called
>>> Set Name  <__main__.AddSetName.<locals>.ClsWithSetName object at 0x0000017F46386348> <class '__main__.T1'> Val1 <super: <class 'Trait'>, <ClsWithSetName object>>

>>> new  <UnboundField(ClsWithSetName, ('username',), {'validators': [<class 'wtforms.validators.DataRequired'>]})>

如果我们在 new 钩子中刷出“返回”指令，则不会调用 init 或 set_name。 同时，打印显示原始 new 调用为 'Trait' 字段返回一个对象（在特定地址），而在 StringField 的情况下它不返回一个对象（没有关联的地址with)，而是一个名为“UnboundField”的类。 但是，不从 new 返回对象是一种不寻常的行为，对象实例的丢失使得 init 或 set_name 的调用毫无意义。

这可能会回答我的问题“为什么不调用 set_name”，但它没有提供模仿它的替代方法。