def process_ubls(ubls):
    """
    Return list of tuples of unique-baseline pairs from command line argument.

    Input:
       comma-separated value of baseline pairs (formatted as "b1_b2")
    Output:
       list of tuples containing unique baselines
    """
    # test that there are ubls to process
    if ubls == '':
        return []
    else:
        ubaselines = []
        for bl in ubls.split(','):
            try:
                i, j = bl.split('_')
                ubaselines.append((int(i), int(j)))
            except ValueError:
                raise AssertionError(
                    "ubls must be a comma-separated list of baselines (formatted as b1_b2)")
        return ubaselines