gistfile1.py

def singleton(cls):
    instances = {}
    def getinstance():
        if cls not in instances:
            instances[cls] = cls()
        return instances[cls]
    return getinstance

@singleton
class MyClass:
    def __init__(self):
        print "creating"

if __name__ == "__main__":
    foo = MyClass()
    bar = MyClass()

    if foo == bar:
        print "nice!"