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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 channels(self):
 """ Access the channels :returns: twilio.rest.chat.v2.service.channel.ChannelList :rtype: twilio.rest.chat.v2.service.channel.ChannelList """

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