docs: def trim(hdu):
      """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])
      if opt.verbose:
          print "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