Python NotificationsManager and observer

gistfile1.py

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]

class observes(object):
    def __init__(self, name):
        self.name = name

    def __call__(self, f):
        def wrapped_f(*args, **kwargs):
            return f(*args, **kwargs)

        NotificationsManager().register(self.name, wrapped_f)
        return wrapped_f


class NotificationsManager(object):
    __metaclass__ = Singleton

    def __init__(self):
        self.observers = dict()

    def register(self, name, observer):
        self.__verify_initialized(name)

        if observer not in self.observers[name]:
            self.observers[name].append(observer)

    def unregister(self, name, observer):
        self.__verify_initialized(name)

        if observer in self.observers[name]:
            self.observers[name].remove(observer)

    def unregister_all(self):
        self.observers.clear()

    def notify(self, name, *args, **kwargs):
        self.__verify_initialized(name)

        for observer in self.observers[name]:
            observer(*args, **kwargs)

    def __verify_initialized(self, name):
        if not self.observers.get(name):
            self.observers[name] = []


if __name__ == "__main__":
    class Foo(object):
        @staticmethod
        @observes("my_event")
        def onMyEvent():
            print("Foo.onMyEvent called!")

    NotificationsManager().notify("my_event")