python全棧開發基礎【補充】metaclass(元類)
阿新 • • 發佈:2018-02-19
認識 全棧 rgs bubuko class a alt 創建 繼承 圖片
一、創建類的執行流程
二、元類的認識
什麽是元類呢?在Python3中繼承type的就是元類
二、元類的示例
# 方式一 class MyType(type): ‘‘‘繼承type的就是元類‘‘‘ def __init__(self,*args,**kwargs): print("MyType創建的對象",self) #Foo super(MyType,self).__init__(*args,**kwargs) def __call__(self, *args, **kwargs): obj = super(MyType,self).__call__(*args,**kwargs) print("類創建對象",self,obj) #Foo class Foo(object,metaclass=MyType): # 對象加括號會去執行__call__方法,__call__方法裏面繼承了type的__call__方法 ,type的__call__方法裏面會先執行__new__方法,再去執行__init__方法。 所以,Foo就是用type創建出來的 user = "haiyan" 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 #對象加括號就會去執行__call__方法 class Foo(MyType(‘Zcc‘, (object,), {})): #MyType(‘Zcc‘, (object,), {})相當於class Zcc(object):pass,也就是創建了一個Zcc的類 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 #對象加括號就會去執行__call__方法 def with_metaclass(arg,base): print("類對象",MyType(‘Zcc‘, (base,), {})) return arg(‘Zcc‘, (base,), {}) #返回一個類對象 <class ‘__main__.Zcc‘> class Foo(with_metaclass(MyType,object)): #MyType(‘Zcc‘, (object,), {})相當於class Zcc(object):pass,也就是創建了一個Zcc的類 user = ‘haiyan‘ age = 18 obj = Foo()
附加
class ASD(type): pass qqq = ASD("qwe", (object,), {}) #用ASD這個元類創建了一個(qwe,並且繼承object類的)類 # class ASD(qwe): # pass obj = qqq() # 能創建類的是元類 # 能創建對象的是類 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‘>
python全棧開發基礎【補充】metaclass(元類)