def hide_keys(dictionary, keys_to_hide, new_value='xxx'):
    """
    Return a copy of the given dictionary on which specified keys will be replaced by the new_value word (or 'xxx').

    :param dictionary: a dictionary
    :param keys_to_hide: keys to hide in the output dictionary
    :param new_value: replacement string for keys to hide
    :return: the new dictionary with hidden items
    """
    _new_dict = {}
    for key, value in dictionary.items():
        _new_dict[key] = new_value if key in keys_to_hide else value
    return _new_dict
