def extendListNoDuplicates(listToBeExtended, newItems):
    """Extend list with items without duplicities.

    :param list listToBeExtended: list to be extended
    :param list newItems: new items
    :return: extended list
    :rtype: list

    >>> extendListNoDuplicates([1, 2, 3, 4], [4, 5, 6])
    [1, 2, 3, 4, 5, 6]
    """
    for item in newItems:
        if not item in listToBeExtended:
            listToBeExtended.append(item)

    return listToBeExtended