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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 alpha_senders(self):
 """ Access the alpha_senders :returns: twilio.rest.messaging.v1.service.alpha_sender.AlphaSenderList :rtype: twilio.rest.messaging.v1.service.alpha_sender.AlphaSenderList """

        if self._alpha_senders is None:
            self._alpha_senders = AlphaSenderList(self._version, service_sid=self._solution['sid'], )
        return self._alpha_senders