code: def updateData(self,exten,data):
          
          _extnum=self._interpretExten(exten)
          fimg = fileutil.openImage(self._filename, mode='update', memmap=False)
          fimg[_extnum].data = data
          fimg[_extnum].header = self._image[_extnum].header
          fimg.close()
docs: Write out updated data and header to
              the original input file for this object.