def ctermpep(seq, length, add_stop=False):
    """Get C-terminal peptide

    add_stop will add a '*' to the peptide (total length still equal to
    `length`)

    If length is bigger than seq, it will return the entire seq

    seq is a Bio.Seq.Seq
    """
    if add_stop:
        seq += "*"
    return seq[-length:]