def _format_row(row, colnames, tab):
    """
    Helper function for _repr_html. Formats one row.
    :param row: row of this table
    :param colnames: vector of column names
    :param tab: table, used to get the column keywords
    :return: html-formatted row
    """
    out=""

    out+="\n<tr>"
    for colname in colnames:
        out+="<td style='vertical-align:top; white-space:pre'>"
        out+=_format_cell(row[colname], tab.getcolkeywords(colname))
        out+="</td>\n"
    out+="</tr>\n"
    return out