创建类的两种方式

方式一:class Foo(object,metaclass=type):    CITY = "bj"    def func(self,x):        return x + 1方式二:Foo = type('Foo',(object,),{'CITY':'bj','func':lambda self,x:x+1})

类的演变

演变1:class MyType(type):    def __init__(self,*args,**kwargs):        print('创建类之前')        super(MyType,self).__init__(*args,**kwargs)        print('创建类之后')Base = MyType('Base',(object,),{})# class Base(object,metaclass=MyType):#     passclass Foo(Base):    CITY = "bj"    def func(self, x):        return x + 1演变2:class MyType(type):    def __init__(self,*args,**kwargs):        print('创建类之前')        super(MyType,self).__init__(*args,**kwargs)        print('创建类之后')def with_metaclass(arg):    return MyType('Base',(arg,),{}) # class Base(object,metaclass=MyType): passclass Foo(with_metaclass(object)):    CITY = "bj"    def func(self, x):        return x + 1演变3:class MyType(type):    def __init__(self,*args,**kwargs):        super(MyType,self).__init__(*args,**kwargs)class Foo(object,metaclass=MyType):

总结

1. 默认类由type实例化创建。2. 某个类指定metaclass=MyType，那么当前类的所有派生类都由于MyType创建。3. 实例化对象    - type.__init__             - type.__call__    - 类.__new__    - 类.__init__