def prettylist(list_):
    """
    Filter out duplicate values while keeping order.
    """
    if not list_:
        return ''

    values = set()
    uniqueList = []

    for entry in list_:
        if not entry in values:
            values.add(entry)
            uniqueList.append(entry)

    return uniqueList[0] if len(uniqueList) == 1 \
        else '[' + '; '.join(uniqueList) + ']'
Filter out duplicate values while keeping order.