def remove_duplicates(seq, keep=()):
    """

    Remove duplicates from a sequence while perserving order.

    The optional tuple argument "keep" can be given to specificy 
    each string you don't want to be removed as a duplicate.
    """
    seq2 = []
    seen = set();
    for i in seq:
        if i in (keep):
            seq2.append(i)
            continue
        elif i not in seen:
            seq2.append(i)
        seen.add(i)
    return seq2