def split_exons(exons):
    """
    Return a list of the s-exons in the string.

    >>> split_exons('3_0/3_1')
    ['3_0', '3_1']
    >>> split_exons('4_0')
    ['4_0']
    """
    if '/' in exons:
        return exons.split('/')
    return [exons]
