import copy


def _merge_list_of_scalars(dst, src):
    """Merge list of scalars (add src first, then remaining unique dst)"""
    dst_copy = copy.copy(dst)
    src_set = set(src)
    dst = copy.copy(src)
    for val in dst_copy:
        if val not in src_set:
            dst.append(val)
    return dst