def muzeropad(runs, out):
    """
    muzeropad(runs,out)
        runs is a string containing the run number
    utility of the suite tab, not a method
    future:
    1) determine how many leading zeros for padding
       read a file from data dir
       check number of digits before '.'
       count number of digits in run
       zero pad
    now:
    0) zeroth version pads a fixed number of zeros to 4 digits
    out in mugui is _output_, Textarea for printing messages
    """
    zeros = '0000'
    if len(runs) < len(zeros):
        return zeros[:len(zeros) - len(runs)] + runs
    elif len(runs) == len(zeros):
        return runs
    else:
        with out:
            print('Too long run number!')
        return []
