一、创建类的流程
二、什么是元类
在Python3中继承type的就是元类
示例
# 方式一 class MyType(type): ‘‘‘继承type的就是元类‘‘‘ def __init__(self,*args,**kwargs): print("MyType创建的对象",self) #Foo super(MyType,self).__init__(*args,**kwargs) def __call__(self, *args, **kwargs): obj = super(MyType,self).__call__(*args,**kwargs) print("类创建对象",self,obj) #Foo class Foo(object,metaclass=MyType): # 对象加括号会去执行__call__方法，__call__方法里面继承了type的__call__方法 ，type的__call__方法里面会先执行__new__方法，再去执行__init__方法。 所以，Foo就是用type创建出来的 user = "haha" age = 18 obj = Foo()
# 方式二 class MyType(type): def __init__(self, *args, **kwargs): print("ssss") super(MyType, self).__init__(*args, **kwargs) def __call__(cls, *args, **kwargs): v = dir(cls) obj = super(MyType, cls).__call__(*args, **kwargs) return obj #对象加括号就会去执行__call__方法 class Foo(MyType(‘Zcc‘, (object,), {})): #MyType(‘Zcc‘, (object,), {})相当于class Zcc(object):pass,也就是创建了一个Zcc的类 user = ‘haiyan‘ age = 18 obj = Foo()
# 方式三 class MyType(type): def __init__(self, *args, **kwargs): print("ssss") super(MyType, self).__init__(*args, **kwargs) def __call__(cls, *args, **kwargs): v = dir(cls) obj = super(MyType, cls).__call__(*args, **kwargs) return obj #对象加括号就会去执行__call__方法 def with_metaclass(arg,base): print("类对象",MyType(‘Zcc‘, (base,), {})) return arg(‘Zcc‘, (base,), {}) #返回一个类对象 <class ‘__main__.Zcc‘> class Foo(with_metaclass(MyType,object)): #MyType(‘Zcc‘, (object,), {})相当于class Zcc(object):pass,也就是创建了一个Zcc的类 user = ‘haiyan‘ age = 18 obj = Foo()
class ASD(type): pass qqq = ASD("qwe", (object,), {}) #用ASD这个元类创建了一个（qwe,并且继承object类的）类 # class ASD(qwe): # pass obj = qqq() # 能创建类的是元类 # 能创建对象的是类 print(obj) #<__main__.qwe object at 0x00000000024FFBA8> print(obj.__class__) #<class ‘__main__.qwe‘> print(obj.__class__.__class__) #<class ‘__main__.ASD‘> print(obj.__class__.__class__.__class__) #<class ‘type‘> print(obj.__class__.__class__.__class__.__class__) #<class ‘type‘>
