def _uniq(input_list):
    """
    Return a list of unique elements of a list of elements
    while preserving the order.

    The function adopted from Lukas comment of 13/01/2016
    at https://www.peterbe.com/plog/uniqifiers-benchmark.

    Args:
        input_list(list): the processed list of elements.

    Returns the list of unique elements of the input list.
    """
    seen = set()
    seen_add = seen.add
    return [x for x in input_list if not (x in seen or seen_add(x))]