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 
 20  t1 = Test.getSingleton()
 21  t2 = Test.getSingleton()
 22  
 23  t1.test()
 24  t2.test()
 25  assert(isinstance(t1,Test))
 26  assert(isinstance(t2,Test))
 27  assert(id(t1)==id(t2))
 28 
 29  t1 = Test1.getSingleton()
 30  t2 = Test1.getSingleton()
 31 
 32  assert(isinstance(t1,Test1))
 33  assert(isinstance(t2,Test1))
 34  assert(id(t1)==id(t2))
 35  
 36  t1.test()
 37  t1.test1()
 38  t2.test()
 39  t1.test1()
 40 
 41  t3 = Test.getSingleton()
 42  
 43  t3.test()
 44  assert(isinstance(t3,Test))