def _verify_checksum_datasum(self, blocking):
        """
        Verify the checksum/datasum values if the cards exist in the header.
        Simply displays warnings if either the checksum or datasum don't match.
        """

        # NOTE:  private data members _checksum and _datasum are
        # used by the utility script "fitscheck" to detect missing
        # checksums.

        if self._header in 'CHECKSUM':
            self._checksum = self._header['CHECKSUM']
            self._checksum_comment = self._header.comments['CHECKSUM']
            if not self.verify_checksum(blocking):
                warnings.warn('Checksum verification failed for HDU %s.\n' %
                              ((self.name, self.ver),))
        else:
            self._checksum = None
            self._checksum_comment = None

        if 'DATASUM' in self._header:
            self._datasum = self._header['DATASUM']
            self._datasum_comment = self._header.comments['DATASUM']

            if not self.verify_datasum(blocking):
                warnings.warn('Datasum verification failed for HDU %s.\n' %
                              ((self.name, self.ver),))
        else:
            self._checksum = None
            self._checksum_comment = None
            self._datasum = None
            self._datasum_comment = None
dataset/ETHPy150Open spacetelescope/PyFITS/pyfits/hdu/base.py/_ValidHDU._verify_checksum_datasum/swapped operands of `in`