单胎级工厂

Question

要创建Singleton u，可以这样做：

class Klass:

    def __new__(cls, args):
        if not hasattr(cls, 'instance'):
            cls.instance = Blah(args)
        return cls.instance

是否有办法按需创建Singleton类，即：

  SingletonFactory('Klass1')
  obj11 = Klass1(args)
  obj12 = Klass1(args)
  #obj11 == obj12 ==> true

  SingletonFactory('Klass2')
  obj21 = Klass2(args)
  obj22 = Klass2(args)
  #obj21 == obj22 ==> true

  #obj11 == obj22 ==> false

底层类仍然是Blah。

Answer 1

这是我的解决办法

def singleton(new_klass, klass): 

    def new(cls, *args, **kvargs):
        if not hasattr(cls, 'instance'):
            cls.instance = klass(*args, **kvargs)
        return cls.instance


    globals()[new_klass] = type(new_klass, (object,), {'__new__' : new})
    #return type(new_klass, (object,), {'__new__' : new})


singleton('C1',Blah)
c1 = C1(10,10)
c2 = C1(10,10)

c1 == c2  #true

singleton('C2',Blah)
c3 = C2(10,10)


c1 == c3  #false