code: def merged_cell_ranges(self):
      
      for row_number, row in enumerate(self.raw_sheet.rows()):
        for col_number, cell in enumerate(row):
          rspan, cspan = cell.span
          if (rspan, cspan) != (1, 1):
            yield ((col_number, row_number), (col_number + cspan, row_number + rspan))
docs: Generates the sequence of merged cell ranges in the format:
  
      ((col_low, row_low), (col_hi, row_hi))