How to use the tablib.packages.openpyxl3.cell.get_column_letter function in tablib

if ':' in range_string:
            # R1C1 range
            result = []
            min_range, max_range = range_string.split(':')
            min_col, min_row = coordinate_from_string(min_range)
            max_col, max_row = coordinate_from_string(max_range)
            if column:
                min_col = get_column_letter(
                        column_index_from_string(min_col) + column)
                max_col = get_column_letter(
                        column_index_from_string(max_col) + column)
            min_col = column_index_from_string(min_col)
            max_col = column_index_from_string(max_col)
            cache_cols = {}
            for col in range(min_col, max_col + 1):
                cache_cols[col] = get_column_letter(col)
            rows = range(min_row + row, max_row + row + 1)
            cols = range(min_col, max_col + 1)
            for row in rows:
                new_row = []
                for col in cols:
                    new_row.append(self.cell('%s%s' % (cache_cols[col], row)))
                result.append(tuple(new_row))
            return tuple(result)
        else:
            try:
                return self.cell(coordinate = range_string, row = row,
                        column = column)
            except CellCoordinatesException:
                pass

            # named range

:type row: int

        :param column: number of columns to offset
        :type column: int

        :rtype: tuples of tuples of :class:`.cell.Cell`

        """
        if ':' in range_string:
            # R1C1 range
            result = []
            min_range, max_range = range_string.split(':')
            min_col, min_row = coordinate_from_string(min_range)
            max_col, max_row = coordinate_from_string(max_range)
            if column:
                min_col = get_column_letter(
                        column_index_from_string(min_col) + column)
                max_col = get_column_letter(
                        column_index_from_string(max_col) + column)
            min_col = column_index_from_string(min_col)
            max_col = column_index_from_string(max_col)
            cache_cols = {}
            for col in range(min_col, max_col + 1):
                cache_cols[col] = get_column_letter(col)
            rows = range(min_row + row, max_row + row + 1)
            cols = range(min_col, max_col + 1)
            for row in rows:
                new_row = []
                for col in cols:
                    new_row.append(self.cell('%s%s' % (cache_cols[col], row)))
                result.append(tuple(new_row))
            return tuple(result)

:param column: number of columns to offset
        :type column: int

        :rtype: tuples of tuples of :class:`.cell.Cell`

        """
        if ':' in range_string:
            # R1C1 range
            result = []
            min_range, max_range = range_string.split(':')
            min_col, min_row = coordinate_from_string(min_range)
            max_col, max_row = coordinate_from_string(max_range)
            if column:
                min_col = get_column_letter(
                        column_index_from_string(min_col) + column)
                max_col = get_column_letter(
                        column_index_from_string(max_col) + column)
            min_col = column_index_from_string(min_col)
            max_col = column_index_from_string(max_col)
            cache_cols = {}
            for col in range(min_col, max_col + 1):
                cache_cols[col] = get_column_letter(col)
            rows = range(min_row + row, max_row + row + 1)
            cols = range(min_col, max_col + 1)
            for row in rows:
                new_row = []
                for col in cols:
                    new_row.append(self.cell('%s%s' % (cache_cols[col], row)))
                result.append(tuple(new_row))
            return tuple(result)
        else:
            try:

STYLES = {'datetime' : {'type':Cell.TYPE_NUMERIC,
                        'style':'1'},
          'string':{'type':Cell.TYPE_STRING,
                    'style':'0'},
          'numeric':{'type':Cell.TYPE_NUMERIC,
                     'style':'0'},
          'formula':{'type':Cell.TYPE_FORMULA,
                    'style':'0'},
          'boolean':{'type':Cell.TYPE_BOOL,
                    'style':'0'},
        }

DATETIME_STYLE = Style()
DATETIME_STYLE.number_format.format_code = NumberFormat.FORMAT_DATE_YYYYMMDD2 
BOUNDING_BOX_PLACEHOLDER = 'A1:%s%d' % (get_column_letter(MAX_COLUMN), MAX_ROW)

class DumpWorksheet(Worksheet):

    """
    .. warning::

        You shouldn't initialize this yourself, use :class:`..workbook.Workbook` constructor instead, 
        with `optimized_write = True`.
    """

    def __init__(self, parent_workbook):

        Worksheet.__init__(self, parent_workbook)

        self._max_col = 0
        self._max_row = 0

def columns(self):

        max_row = self.get_highest_row()

        cols = []

        for col_idx in range(self.get_highest_column()):
            col = get_column_letter(col_idx+1)
            res = self.range('%s1:%s%d' % (col, col, max_row))
            cols.append(tuple([x[0] for x in res]))


        return tuple(cols)

:param column: column index of the cell (e.g. 3)
        :type column: int

        :raise: InsufficientCoordinatesException when coordinate or (row and column) are not given

        :rtype: :class:`.cell.Cell`

        """
        if not coordinate:
            if  (row is None or column is None):
                msg = "You have to provide a value either for " \
                        "'coordinate' or for 'row' *and* 'column'"
                raise InsufficientCoordinatesException(msg)
            else:
                coordinate = '%s%s' % (get_column_letter(column + 1), row + 1)
        else:
            coordinate = coordinate.replace('$', '')

        return self._get_cell(coordinate)

def get_squared_range(p, min_col, min_row, max_col, max_row, string_table, style_table):

    expected_columns = [get_column_letter(ci) for ci in range(min_col, max_col)]

    current_row = min_row
    for row, cells in get_rows(p, min_row = min_row, max_row = max_row, min_column = min_col, max_column = max_col):
        full_row = []
        if current_row < row:

            for gap_row in range(current_row, row):

                dummy_cells = get_missing_cells(gap_row, expected_columns)
                
                yield tuple([dummy_cells[column] for column in expected_columns])

                current_row = row

        temp_cells = list(cells)