import string


def prefixTrackName(filename):       
    """
    santitize trackName. Because track name must begin with a letter and
    contain only the following chars: [a-zA-Z0-9_].
    See the "track" Common settings at:
    https://genome.ucsc.edu/goldenpath/help/trackDb/trackDbHub.html#bigPsl_-_Pairwise_Alignments
    skip the santitization for cytoBandIdeo track
    """
    if filename == 'cytoBandIdeo':
        return filename
    valid_chars = "_%s%s" % (string.ascii_letters, string.digits)
    sanitize_name = ''.join([c if c in valid_chars else '_' for c in filename])
    sanitize_name = "gonramp_" + sanitize_name
    return sanitize_name