code: def _extract_input_connections(self):
      
      for con in self.connections:
        ends = con.strip().split('<->')  # [host1:port1->host2]
        ends = filter(None, ends)  # Remove '' elements
        if len(ends) == 0:
          continue
        if len(ends) > 0:
          host1, port1 = self._get_tuple(ends[0].split(':'))
        host2 = ''
        port2 = ''
        if len(ends) > 1:
          host2, port2 = self._get_tuple(ends[1].split(':'))
        self.input_connections.append((host1, port1, host2, port2))
docs: Given user input of interested connections, it will extract the info and output a list of tuples.
      - input can be multiple values, separated by space;
      - either host or port is optional
      - it may be just one end,
      - e.g., "host1<->host2 host3<->  host1:port1<->host2"
      :return: None