#------------------------------------------------------------------------------
#  LineReverse.py
#  Reverses the word order of every line in a file
#------------------------------------------------------------------------------
import sys

# usage()
# Prints error messages to stderr
def usage():
   print("Usage: $ python3 LineReverse.py <input file> <output file>", 
         file=sys.stderr)
   exit()
# end


def main():

   # check command line arguments and open files
   if len(sys.argv)!=3:
      usage()
   # end
   try:
      infile = open(sys.argv[1])
   except FileNotFoundError as e:
      print(e, file=sys.stderr)
      usage()
   # end
   outfile = open(sys.argv[2], 'w')

   # read in each line of infile, reverse it, then print to outfile
   lines = infile.readlines()
   for S in lines:
      L = S.split()
      L.reverse()
      R = ' '.join(L)
      print(R, file=outfile)
   # end

   infile.close()
   outfile.close()

# end

#------------------------------------------------------------------------------
if __name__=='__main__':

   main()

# end