old_contents: #! /usr/bin/env python
  # -*- coding: utf-8 -*-
  # Adds my copyright notice to photos.
  #
  # Author: R.F. Smith <rsmith@xs4all.nl>
  # $Date$
  #
  # To the extent possible under law, Roland Smith has waived all copyright and
  # related or neighboring rights to markphotos.py. This work is published from
  # the Netherlands. See http://creativecommons.org/publicdomain/zero/1.0/
  
  import sys
  import subprocess
  from multiprocessing import Pool, Lock
  from os import utime, devnull
  import os.path
  from time import mktime
  
  globallock = Lock() 
  
  def processfile(name):
      args = ['exiftool', '-CreateDate', name]
      createdate = subprocess.check_output(args)
      fields = createdate.split(":") #pylint: disable=E1103
      year = int(fields[1])
      cr = "R.F. Smith <rsmith@xs4all.nl> http://rsmith.home.xs4all.nl/"
      cmt = "Copyright © {} {}".format(year, cr)
      args = ['exiftool', '-Copyright="Copyright (C) {} {}"'.format(year, cr),
              '-Comment="{}"'.format(cmt), '-overwrite_original', '-q', name]
      rv = subprocess.call(args)
      modtime = int(mktime((year, int(fields[2]), int(fields[3][:2]),
                            int(fields[3][3:]), int(fields[4]), int(fields[5]),
                            0,0,-1)))
      utime(name, (modtime, modtime))
      globallock.acquire()
      if rv == 0:
          print "File '{}' processed.".format(name)
      else:
          print "Error when processing file '{}'".format(name)
      globallock.release()
  
  def checkfor(args):
      """Make sure that a program necessary for using this script is
      available."""
      if isinstance(args, str):
          args = args.split()
      try:
          with open(devnull, 'w') as f:
              subprocess.call(args, stderr=subprocess.STDOUT, stdout=f)
      except:
          print "Required program '{}' not found! exiting.".format(args[0])
          sys.exit(1)
  
  def main(argv):
      """Main program.
  
      Keyword arguments:
      argv -- command line arguments
      """
      if len(argv) == 1:
          binary = os.path.basename(argv[0])
          print "Usage: {} [file ...]".format(binary)
          sys.exit(0)
      checkfor(['exiftool',  '-ver'])
      p = Pool()
      p.map(processfile, argv[1:])
      p.close()
  
  if __name__ == '__main__':
      main(sys.argv)
  
new_contents: #! /usr/bin/env python
  # -*- coding: utf-8 -*-
  # Adds my copyright notice to photos.
  #
  # Author: R.F. Smith <rsmith@xs4all.nl>
  # $Date$
  #
  # To the extent possible under law, Roland Smith has waived all copyright and
  # related or neighboring rights to markphotos.py. This work is published from
  # the Netherlands. See http://creativecommons.org/publicdomain/zero/1.0/
  
  import sys
  import subprocess
  from multiprocessing import Pool, Lock
  from os import utime, devnull
  import os.path
  from time import mktime
  from checkfor import checkfor
  
  globallock = Lock() 
  
  def processfile(name):
      args = ['exiftool', '-CreateDate', name]
      createdate = subprocess.check_output(args)
      fields = createdate.split(":") #pylint: disable=E1103
      year = int(fields[1])
      cr = "R.F. Smith <rsmith@xs4all.nl> http://rsmith.home.xs4all.nl/"
      cmt = "Copyright © {} {}".format(year, cr)
      args = ['exiftool', '-Copyright="Copyright (C) {} {}"'.format(year, cr),
              '-Comment="{}"'.format(cmt), '-overwrite_original', '-q', name]
      rv = subprocess.call(args)
      modtime = int(mktime((year, int(fields[2]), int(fields[3][:2]),
                            int(fields[3][3:]), int(fields[4]), int(fields[5]),
                            0,0,-1)))
      utime(name, (modtime, modtime))
      globallock.acquire()
      if rv == 0:
          print "File '{}' processed.".format(name)
      else:
          print "Error when processing file '{}'".format(name)
      globallock.release()
  
  def main(argv):
      """Main program.
  
      Keyword arguments:
      argv -- command line arguments
      """
      if len(argv) == 1:
          binary = os.path.basename(argv[0])
          print "Usage: {} [file ...]".format(binary)
          sys.exit(0)
      checkfor(['exiftool',  '-ver'])
      p = Pool()
      p.map(processfile, argv[1:])
      p.close()
  
  if __name__ == '__main__':
      main(sys.argv)
  
subject: Put checkfor in a separate module.