調用object .__ new__會發生什么？

Question

1. 老式類

    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. 新型班

    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> >>> 

我想了解在調用object.__new__的兩個版本的代碼中會發生什么？

Answer 1

舊式類不支持 __new__方法：

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

__new__是一種新的類功能。