class Singleton(type):
    _instances = {}
 
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
        return cls._instances[cls]
 
 
# Python2
class MyClass(BaseClass):
    __metaclass__ = Singleton
    pass
 
 
# Python3
class MyClass(BaseClass, metaclass=Singleton):
    pass
 
 
  # Test
  for x in range(5):
    MyClass().x = x
    print(MyClass().x)

* http://stackoverflow.com/questions/6760685/creating-a-singleton-in-python