Returns the current row as a tuple.

def _GetRow(self, columns=None):
        """Returns the current row as a tuple."""

        row = self._table[self._row_index]
        if columns:
            result = []
            for col in columns:
                if col not in self.header:
                    raise TableError("Column header %s not known in table." % col)
                result.append(row[self.header.index(col)])
            row = result
        return row