code: def gather_info_hdu(self, hdulist):
          
          values = {}
          values['n_ext'] = len(hdulist)
          extnames = [hdu.header.get('extname', '') for hdu in hdulist[1:]]
          values['name_ext'] = ['PRIMARY'] + extnames
  
          fits_extractor = self.extractor_map['fits']
          for key in self.meta_dinfo_headers:
              values[key] = fits_extractor.extract(key, hdulist)
  
          return values
docs: Obtain a summary of information about the image.