Singleton

classmethod

pro

You can use both as simple class or as a singleton.
You do not need to write code for each class you want to act as singleton.

cons

   1 # Code is Public Domain.
   2 class Singleton:
   3     _singleton = None
   4     def getSingleton(cls):
   5         if not isinstance(cls._singleton,cls):
   6             cls._singleton = cls()
   7         return cls._singleton
   8 
   9     getSingleton = classmethod(getSingleton)
  10 
  11 if __name__=='__main__':
  12     class Test(Singleton):
  13         def test(self):
  14             print self.__class__,id(self)
  15 
  16     class Test1(Test):
  17         def test1(self):
  18             print self.__class__,id(self),'Test1'
  19