code: def get(self, key, get_cas=False):
          
          for server in self.servers:
              value, cas = server.get(key)
              if value is not None:
                  if get_cas:
                      return value, cas
                  else:
                      return value
          if get_cas:
              return None, None
docs: Get a key from server.
  
          :param key: Key's name
          :type key: six.string_types
          :param get_cas: If true, return (value, cas), where cas is the new CAS value.
          :type get_cas: boolean
          :return: Returns a key data from server.
          :rtype: object