def add_pd_lr(data, var_list, sufix_str):
    """Create the left, right, and sum of the give var_list for a dataframe.
    
    Parameters
    ----------
    data : pandas.DataFrame
        The dataframe which contains the var_list left and right part.
    var_list : :obj:`list` of :obj:`str`
        The list of labels without left or right specified.
    sufix_str : 'str'
        The string for left and right, e.g. Right or rh. etc.
    
    Returns
    -------
    data : pandas.DataFrame
        The dataframe which contains the var_list left, right and sum.
    res_list : :obj:`list` of :obj:`str`
        The newly added columns list.

    """
    left_suf = sufix_str[0]; right_suf = sufix_str[1];
    for x in var_list:
        data[x] = data[left_suf+x]+ data[right_suf+x];
    columns_left   = [ left_suf+x  for x in var_list];
    columns_right  = [ right_suf+x for x in var_list];
    res_list = var_list+columns_left+columns_right;
    return data, res_list