Singleton

borg_pattern.py

class Borg(object):
    _shared_state = {}

    def __new__(cls, *args, **kwargs):
        obj = super(Borg, cls).__new__(cls, *args, **kwargs)
        obj.__dict__ = cls._shared_state
        return obj

class Child(Borg):
    pass

borg = Borg()
another_borg = Borg()

print borg is another_borg 
child = Child()
borg.only_one = "I am the one"
print child.only_one

classic_singleton.py

class Singleton(object):
    def __new__(cls):
        if not hasattr(cls, 'instance'):
            cls.instance = super(Singleton, cls).__new__(cls)
        return cls.instance

singleton = Singleton()
another_singleton = Singleton()

print singleton is another_singleton

singleton.only_one_var = "I'm only one var"
print another_singleton.only_one_var