How to use the bamnostic.bam.BAMheader function in bamnostic

def _load_header(self, check_sq=True):
        """ Loads the header into the reader object

        Args:
            check_sq (bool): whether to check for file header or not (default: True).

        Raises:
            KeyError: If 'SQ' entry is not present in BAM header
        """

        self._header = BAMheader(self)
        self.header = self._header.SAMheader if self._header.SAMheader else self._header
        self.text = self._header._SAMheader_raw

        # make compatible with pysam attributes, even though the data exists elsewhere
        self.__references = []
        self.__lengths = []
        for n in range(self._header.n_refs):
            self.__references.append(self._header.refs[n][0])
            self.__lengths.append(self._header.refs[n][1])
        self.__nreferences = self._header.n_refs

        if check_sq:
            if not self._check_sq():
                raise KeyError('No SQ entries in header')