code: def _getFilename(self, fileNumber):
          
          cur = self._connection.cursor()
          cur.execute('SELECT name FROM files WHERE id = ?', (fileNumber,))
          row = cur.fetchone()
          if row is None:
              return None
          else:
              return row[0]
docs: Given a file number, get its name (if any).
  
          @param fileNumber: An C{int} file number.
          @return: A C{str} file name or C{None} if a file with that number
              has not been added.