code: def __ChannelMaskListToStr(self, channelList):
          
          chan_mask_range = ''
          if isinstance(channelList, list):
              if len(channelList):
                  chan_mask_range = ",".join(str(chan) for chan in channelList)
              else:
                  print 'empty list'
          else:
              print 'not a valid channel list:', channelList
  
          return chan_mask_range
docs: convert a channel list to a string
  
          Args:
              channelList: channel list (i.e. [21, 22, 23])
  
          Returns:
              a comma separated channel string (i.e. '21, 22, 23')