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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def close(self):
 """ Close the fits file and set relevant metadata to None """

        if hasattr(self, '_FITS'):
            if self._FITS is not None:
                self._FITS.close()
                self._FITS = None
        self._filename = None
        self.mode = None
        self.charmode = None
        self.intmode = None
        self.hdu_list = None
        self.hdu_map = None