old_contents: #!/usr/bin/env python2
  import sys, subprocess
  import re
  
  if __name__ == '__main__':
      p = subprocess.Popen(sys.argv[1:], stderr=subprocess.PIPE)
      (stdout, stderr) = p.communicate()
      reg = re.compile(r'''Warning(: in file .*?,\s*required library .*? matches several files in path)''')
      if reg.search(stderr):
          sys.stderr.write(reg.sub(r'Error\1', stderr))
          sys.exit(1)
      sys.stderr.write(stderr)
      sys.exit(p.returncode)
  
new_contents: #!/usr/bin/env python3
  import sys, subprocess
  import re
  
  if __name__ == '__main__':
      p = subprocess.Popen(sys.argv[1:], stderr=subprocess.PIPE)
      (stdout, stderr) = p.communicate()
      stderr = stderr.decode('utf-8')
      reg = re.compile(r'''Warning(: in file .*?,\s*required library .*? matches several files in path)''')
      if reg.search(stderr):
          sys.stderr.write(reg.sub(r'Error\1', stderr))
          sys.exit(1)
      sys.stderr.write(stderr)
      sys.exit(p.returncode)
  
subject: Switch from python2 to python3