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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 ip_addresses(self):
 """ Access the ip_addresses :returns: twilio.rest.api.v2010.account.sip.ip_access_control_list.ip_address.IpAddressList :rtype: twilio.rest.api.v2010.account.sip.ip_access_control_list.ip_address.IpAddressList """

        if self._ip_addresses is None:
            self._ip_addresses = IpAddressList(
                self._version,
                account_sid=self._solution['account_sid'],
                ip_access_control_list_sid=self._solution['sid'],
            )
        return self._ip_addresses