def _get_channel_num(port_grp):
    """ Return a channel number given a port group.  The lowest value
    port number in the group is returned.  No checks are made to insure
    that all ports are in the same chassis.
    Args:
        port_group: (tuple or list of str representing port numbers
        of the form 'n' or 'm/n' or 'ethm/n' or similar
    """
    return min([int(port_grp[i].rpartition('/')[-1])
               for i in range(len(port_grp))])