code: def open(self):
          
  
          if self.handle is None:
              self.handle = fits.open(self.fname, mode='readonly')
  
          if self.extn:
              if len(self.extn) == 1:
                  hdu = self.handle[self.extn[0]]
              else:
                  hdu = self.handle[self.extn[0],self.extn[1]]
          else:
              hdu = self.handle[0]
          if isinstance(hdu,fits.hdu.compressed.CompImageHDU):
              self.compress = True
          return hdu
docs: Opens the file for subsequent access.