1 class A(object):
2     def __init__(self,*args, **kwargs):
3         print "init A"
4     def __new__(cls,*args, **kwargs):
5         print "new A %s"%cls
6 　　　　 #return super(A, cls).__new__(cls, *args, **kwargs)
7         return object.__new__(cls, *args, **kwargs)

1 class B(A):
2     def __init__(self,*args, **kwargs):
3         print "init B"
4     def __new__(cls,*args, **kwargs):
5         print "new B %s"%cls
6 　　　　 #return super(B, cls).__new__(cls, *args, **kwargs)
7         return object.__new__(cls, *args, **kwargs)

1 class PositiveInteger(int):
2     def __init__(self, value):
3         super(PositiveInteger, self).__init__(self, abs(value))
4
5
6 i = PositiveInteger(-3)
7 print i

class PositiveInteger(int):def __new__(cls, value):return super(PositiveInteger, cls).__new__(cls, abs(value))i = PositiveInteger(-3)
print i

class Singleton(object):def __new__(cls):# 关键在于这，每一次实例化的时候，我们都只会返回这同一个instance对象if not hasattr(cls, 'instance'):cls.instance = super(Singleton, cls).__new__(cls)return cls.instanceobj1 = Singleton()
obj2 = Singleton()obj1.attr1 = 'value1'
print obj1.attr1, obj2.attr1
print obj1 is obj2

class Singleton(object):__instance = Nonedef __init__(self, *args, **kwargs):passdef __new__(cls, *args, **kwargs):if not cls.__instance:# if not hasattr(cls, 'instance'):cls.__instance = super(Singleton, cls).__new__(cls, *args, **kwargs)cls.__instance.aa = args[0]print type(cls), type(cls.__instance), type(cls.__instance.aa)return cls.__instanceobj1 = Singleton(1, 2, 3, b=2)
obj2 = Singleton(1, 2, 3, b=2)obj1.attr1 = 'value1'
obj2.attr2 = 'value2'
print obj1.attr1, obj1.attr2
print obj1 is obj2
print obj1.aa, obj2.attr1