code: def find_last(fileobj, serial, finishing=False):
          
  
          # For non-muxed streams, look at the last page.
          seek_end(fileobj, 256 * 256)
  
          data = fileobj.read()
          try:
              index = data.rindex(b"OggS")
          except ValueError:
              raise error("unable to find final Ogg header")
          bytesobj = cBytesIO(data[index:])
  
          def is_valid(page):
              return not finishing or page.position != -1
  
          best_page = None
          try:
              page = OggPage(bytesobj)
          except error:
              pass
          else:
              if page.serial == serial and is_valid(page):
                  if page.last:
                      return page
                  else:
                      best_page = page
              else:
                  best_page = None
  
          # The stream is muxed, so use the slow way.
          fileobj.seek(0)
          try:
              page = OggPage(fileobj)
              while True:
                  if page.serial == serial:
                      if is_valid(page):
                          best_page = page
                      if page.last:
                          break
                  page = OggPage(fileobj)
              return best_page
          except error:
              return best_page
          except EOFError:
              return best_page
docs: Find the last page of the stream 'serial'.
  
          If the file is not multiplexed this function is fast. If it is,
          it must read the whole the stream.
  
          This finds the last page in the actual file object, or the last
          page in the stream (with eos set), whichever comes first.
  
          If finishing is True it returns the last page which contains a packet
          finishing on it. If there exist pages but none with finishing packets
          returns None.
  
          Returns None in case no page with the serial exists.
          Raises error in case this isn't a valid ogg stream.
          Raises IOError.