docs: def trim(hdu, datasec='DATASEC'):
      """TRIM a CFHT MEGAPRIME frame  using the DATASEC keyword"""
      datasec = re.findall(r'(\d+)',
                           hdu.header.get(datasec))
      l = int(datasec[0]) - 1
      r = int(datasec[1])
      b = int(datasec[2]) - 1
      t = int(datasec[3])
      logger.info("Trimming [%d:%d,%d:%d]" % ( l, r, b, t))
      hdu.data = hdu.data[b:t, l:r]
      hdu.header.update('DATASEC',
                        "[%d:%d,%d:%d]" % (1, r - l + 1, 1, t - b + 1),
                        comment="Image was trimmed")
      hdu.header.update('ODATASEC',
                        "[%d:%d,%d:%d]" % (l + 1, r, b + 1, t),
                        comment="previous DATASEC")
      return