Python meta-class __metaclass__

<pre name= "code" class= "Python" > #python元类, the class creation process # First calls type.__new__# and then calls the class's constructor class.__init__def toString (c): s    =""; If Type (c) ==tuple:s= "tuple:" For I in C:s+=str (i) s+= "," Return s elif Typ E (c) = = dict:s= "dict:" For K,v in C.items (): s+= "k=%s,v=%s"% (k,v) s+= "," re    Turn S elif type (c) = = list:s= "list:" For I in C:s+=str (i) s+ "," return s Else:return C class Listmetaclass (type): Def __new__ (CLS, name, bases, attr): #对于比较长的代码行, you can use \  Come to the branch #有没有感觉跟C + + define definition of line-breaking feel the same (-><*><-) print (' cls=%s, name=%s,bases=%s,attrs=%s '%        (ToString (CLS), ToString (name), ToString (bases), ToString (attr)))     attr[' Add ']=lambda self,value:self.append (value) return type.__new__ (CLS, name, bases, attr) class MyList (list): __metaclass__ = Listmetaclass If __name__ = = "__main__": MyList = MyList () mylist.add (+) print (myList) def listadd (self,value): Self.appe nd (value) MyList2 = Listmetaclass ("MyList2", (list,), Dict (Add=listadd)) Mylist2=mylist2 () Mylist2.add (10 XX) print (MYLIST2) "" "Program output: Cls=<class ' __main__. Listmetaclass ', Name=mylist,bases=tuple:<type ' list ' >,,attrs=dict:k=__module__,v=__main__,k=__ Metaclass__,v=<class ' __main__. Listmetaclass ' >,[100]cls=<class ' __main__. Listmetaclass ', Name=mylist2,bases=tuple:<type ' list ' >,,attrs=dict:k=add,v=<function listAdd at     0X01AACBB0&GT;,[1000] "" "

Python meta-class __metaclass__