Add a column to the table.

        Arguments:

        fieldname - name of the field to contain the new column of data
        column - column of data, should be a list with as many elements as the
        table has rows
        align - desired alignment for this column - "l" for left, "c" for centre and "r" for right
        valign - desired vertical alignment for new columns - "t" for top, "m" for middle and "b" for bottom

def add_column(self, fieldname, column, align="c", valign="t"):

        """Add a column to the table.

        Arguments:

        fieldname - name of the field to contain the new column of data
        column - column of data, should be a list with as many elements as the
        table has rows
        align - desired alignment for this column - "l" for left, "c" for centre and "r" for right
        valign - desired vertical alignment for new columns - "t" for top, "m" for middle and "b" for bottom"""

        if len(self._rows) in (0, len(column)):
            self._validate_align(align)
            self._validate_valign(valign)
            self._field_names.append(fieldname)
            self._align[fieldname] = align
            self._valign[fieldname] = valign
            for i in range(0, len(column)):
                if len(self._rows) < i+1:
                    self._rows.append([])
                self._rows[i].append(column[i])
        else:
            raise Exception("Column length %d does not match number of rows %d!" % (len(column), len(self._rows)))