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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 __ChannelMaskListToStr(self, channelList):
 """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') """

        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