def set_relative_positions(exons_in_cds: list) ->None:
    """Set relative positions for exons in cds

    :param exons_in_cds:
    :type exons_in_cds: list
    :return: None
    """
    last_exon_end = 0
    for exon in exons_in_cds:
        exon['relative_start'] = last_exon_end + 1
        exon['relative_end'] = exon['relative_start'] + exon['in_cds_length']
        last_exon_end = exon['relative_end']
