798             df = self.opener(self.datafile)

   798             df = self.opener(self.datafile)

   799 

   799 

   800         readahead = max(65536, length)

   800         readahead = max(65536, length)

   801         df.seek(offset)

   801         df.seek(offset)

   802         d = df.read(readahead)

   802         d = df.read(readahead)

   803         self._addchunk(offset, d)

   804         self._addchunk(offset, d)

   804         if readahead > length:

   805         if readahead > length:

   805             return d[:length]

   806             return d[:length]

   806         return d

   807         return d

   807 

   808