code: def _find(self, id_):
          
          cur = self._connection.cursor()
          cur.execute(
              'SELECT fileNumber, offset FROM sequences WHERE id = ?', (id_,))
          row = cur.fetchone()
          if row is None:
              return None
          else:
              return self._getFilename(row[0]), row[1]
docs: Find the filename and offset of a sequence, given its id.
  
          @param id_: A C{str} sequence id.
          @return: A 2-tuple, containing the C{str} file name and C{int} offset
              within that file of the sequence.