code: def _read_top_header(self):
      
      magic = self._fh.read(4)
      l_text = struct.unpack('<i',self._fh.read(4))[0]
      header_text = self._fh.read(l_text).rstrip('\0')
      n_ref = struct.unpack('<i',self._fh.read(4))[0]
      return header_text, n_ref
docs: Read the header text and number of reference seqs