当你调用object .__ new__时会发生什么？

Question

1. 旧式类

   class Person(): 
       _names_cache = {} 
       def __init__(self,name): 
        self.name = name 
       def __new__(cls,name): 
        return cls._names_cache.setdefault(name,object.__new__(cls,name)) 
   
   ahmed1 = Person("Ahmed") 
   ahmed2 = Person("Ahmed") 
   print ahmed1 is ahmed2 
   print ahmed1 
   print ahmed2 
   
   
   >>> False 
   <__main__.Person instance at 0xb74acf8c> 
   <__main__.Person instance at 0xb74ac6cc> 
   >>> 
   

2. 新式类

   class Person(object): 
       _names_cache = {} 
       def __init__(self,name): 
        self.name = name 
       def __new__(cls,name): 
        return cls._names_cache.setdefault(name,object.__new__(cls,name)) 
   
   ahmed1 = Person("Ahmed") 
   ahmed2 = Person("Ahmed") 
   print ahmed2 is ahmed1 
   print ahmed1 
   print ahmed2 
   
   >>> True 
   <__main__.Person object at 0xb74ac66c> 
   <__main__.Person object at 0xb74ac66c> 
   >>> 
   

我想了解的代码的两个版本会发生什么，当我打电话object.__new__？

Answer 1

老式类不支持一个__new__方法：

>>> class Foo: 
...  def __new__(self, *args, **kw): 
...   print 'Nope' 
... 
>>> Foo() 
<__main__.Foo instance at 0x101f5c908> 

__new__只是一个新式类的功能。