def list_merge(list_a, list_b):
    """
    Merge two lists without duplicating items

    Args:
      list_a: list
      list_b: list
    Returns:
      New list with deduplicated items from list_a and list_b
    """
    # return list(collections.OrderedDict.fromkeys(list_a + list_b))
    result = []
    for item in list_a:
        if item not in result:
            result.append(item)
    for item in list_b:
        if item not in result:
            result.append(item)
    return result