code: def _to_addr(worksheet, row, col, row_fixed=False, col_fixed=False):
      
      addr = ""
      A = ord('A')
      col += 1
      while col > 0:
          addr = chr(A + ((col - 1) % 26)) + addr
          col = (col - 1) // 26
  
      prefix = ("'%s'!" % worksheet) if worksheet else ""
      col_modifier = "$" if col_fixed else ""
      row_modifier = "$" if row_fixed else ""
      return prefix + "%s%s%s%d" % (col_modifier, addr, row_modifier, row+1)
docs: converts a (0,0) based coordinate to an excel address