def find_duplicates(_list):
    """a more efficient way to return duplicated items
    ref: https://www.iditect.com/guide/python/python_howto_find_the_duplicates_in_a_list.html

    :arg list _list: a python list
    """
    first_seen = set()
    first_seen_add = first_seen.add
    duplicates = set(i for i in _list if i in first_seen or first_seen_add(i))
    # turn the set into a list (as requested)
    return duplicates