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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 roles(self):
 """ Access the roles :returns: twilio.rest.chat.v2.service.role.RoleList :rtype: twilio.rest.chat.v2.service.role.RoleList """

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