old_contents: import argparse
  import os
  import re
  import sys
  
  def main(cmdline):
  
      parser = argparse.ArgumentParser(
          description='Ensure zero padding in numbering of files.')
      parser.add_argument('path', type=str,
          help='path to the directory containing the files')
      args = parser.parse_args()
      path = args.path
  
      numbered = re.compile(r'(.*?)(\d+)\.(.*)')
  
      numbered_fnames = [fname for fname in os.listdir(path)
                         if numbered.search(fname)]
  
      max_digits = max(len(numbered.search(fname).group(2))
                       for fname in numbered_fnames)
  
      for fname in numbered_fnames:
          _, prefix, num, ext, _  = numbered.split(fname, maxsplit=1)
          num = num.zfill(max_digits)
          new_fname = "{}{}.{}".format(prefix, num, ext)
          if fname != new_fname:
              os.rename(os.path.join(path, fname), os.path.join(path, new_fname))
              print "Renamed {} to {}".format(fname, new_fname)
          else:
              print "{} seems fine".format(fname)
  
  if __name__ == "__main__":
      sys.exit(main(sys.argv[1:]))
  
  
new_contents: #!/usr/bin/env python3
  
  import argparse
  import os
  import re
  import sys
  
  
  def main():
  
      parser = argparse.ArgumentParser(
          description='Ensure zero padding in numbering of files.')
      parser.add_argument(
          'path',
          type=str,
          help='path to the directory containing the files')
      args = parser.parse_args()
      path = args.path
  
      numbered = re.compile(r'(.*?)(\d+)\.(.*)')
  
      numbered_fnames = [fname for fname in os.listdir(path)
                         if numbered.search(fname)]
  
      max_digits = max(len(numbered.search(fname).group(2))
                       for fname in numbered_fnames)
  
      for fname in numbered_fnames:
          _, prefix, num, ext, _ = numbered.split(fname, maxsplit=1)
          num = num.zfill(max_digits)
          new_fname = "{}{}.{}".format(prefix, num, ext)
          if fname != new_fname:
              os.rename(
                  os.path.join(path, fname),
                  os.path.join(path, new_fname))
              print("Renamed {} to {}".format(fname, new_fname))
          else:
              print("{} seems fine".format(fname))
  
  if __name__ == "__main__":
      sys.exit(main())
  
subject: Convert to py3, fix style issues (flake8, pylint).