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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get(cls):
 """ Acquires the NotificationManager service async. """

        app = AndroidApplication.instance()
        f = app.create_future()

        if cls._instance:
            f.set_result(cls._instance)
            return f

        def on_service(obj_id):
            #: Create the manager
            if not cls.instance():
                m = cls(__id__=obj_id)
            else:
                m = cls.instance()
            f.set_result(m)

        cls.from_(app).then(on_service)

        return f