python元编程2【type类创建对象2种方法】

0. 参考资料

https://www.liaoxuefeng.com/wiki/1016959663602400/1017592449371072
https://stackoverflow.com/questions/18513821/python-metaclass-understanding-the-with-metaclass

1. return type(name, bases, attr) 和 return type.new(cls, 'name',(object,), {})

# # type 类创建对象方法1【class_ = ModelObject('name',(Test,),{})】
class SetterAwareType(type):    # 元类
    def __new__(cls, *args):
        print('in SetterAwareType __new__')
        return type.__new__(cls, *args)   # return 方式1,这种方式执行__init__函数
        name, bases, attr = args[:3]
        return type(name, bases, attr)     # return 方式2 ,这种方式不走__init__函数了，不打印 in SetterAwareType __init__

    def __init__(cls,  *args):
        print('in SetterAwareType __init__')
        return type.__init__(cls, *args)   # TypeError: type.__init__() takes 1 or 3 arguments

class ModelObject(SetterAwareType):
    pass

class Test(object):
    def test(self):
        print('in class Test test')

class_ = ModelObject('name',(Test,),{})
obj = class_()
obj.test()



# type 类创建对象方法2【a = ModelObject()】
class SetterAwareType(type):    # 元类
    def __new__(cls, *args):
        print('in SetterAwareType __new__')
        return type.__new__(cls, 'name',(object,), {})  # 'name' 直接传入了

    def __init__(cls,  *args):
        print('in SetterAwareType __init__')
        return super(SetterAwareType, cls).__init__(cls,  *args)
        # return type.__init__(cls, *args)   # TypeError: type.__init__() takes 1 or 3 arguments


class ModelObject(SetterAwareType):
    def test(self):
        print('in ModelObject copy')

a = ModelObject()
a.test()