old_contents: #!/usr/bin/env python
  
  import os
  import sys
  from string import Template
  import argparse
  import hashlib
  
  if __name__ == "__main__":
      parser = argparse.ArgumentParser(description='Rename files based on content.')
  
      parser.add_argument('files', metavar='FILE', type=str, nargs='+',
                         help='Files to rename')
      parser.add_argument('-m', '--mask', nargs='?',
                         help='File destination mask', default='${hash}.${ext}')
      parser.add_argument('-p', '--pretend', action='store_true',
                         help='Do not rename, just print')
  
      args = parser.parse_args()
      print 'Renaming with mask: %s' % args.mask
      mask = Template(args.mask)
      for f in args.files:
          if not os.path.exists(f):
              print >>sys.stderr, 'File %s does not exists.' % f
          else:
              with open(f) as fp:
                  h = hashlib.sha1(fp.read()).hexdigest()
              ext = os.path.splitext(f)[1][1:]
              name = mask.substitute(hash=h, ext=ext)
              dest = os.path.join(os.path.dirname(f), name)
              print "`%s' -> `%s'" % (f, dest)
              if os.path.exists(dest):
                  print >>sys.stderr, 'Destination %s already exists.' % dest
              elif not args.pretend:
                  os.rename(f, dest)
  
new_contents: #!/usr/bin/env python
  
  import os
  import sys
  from string import Template
  import argparse
  import hashlib
  
  if __name__ == "__main__":
      parser = argparse.ArgumentParser(description='Rename files based on content.')
  
      parser.add_argument('files', metavar='FILE', type=str, nargs='+',
                         help='Files to rename')
      parser.add_argument('-m', '--mask', nargs='?',
                         help='File destination mask', default='${hash}.${ext}')
      parser.add_argument('-p', '--pretend', action='store_true',
                         help='Do not rename, just print')
  
      args = parser.parse_args()
      print 'Renaming with mask: %s' % args.mask
      mask = Template(args.mask)
      for f in args.files:
          if not os.path.exists(f):
              print >>sys.stderr, 'File %s does not exists.' % f
          else:
              with open(f) as fp:
                  h = hashlib.sha1(fp.read()).hexdigest()
              ext = os.path.splitext(f)[1][1:]
              name = mask.substitute(hash=h, ext=ext)
              dest = os.path.join(os.path.dirname(f), name)
              if os.path.basename(f) == name:
                  print 'OK %s' % name
              else:
                  print "`%s' -> `%s'" % (f, dest)
                  if os.path.exists(dest):
                      print >>sys.stderr, 'Destination %s already exists.' % dest
                  elif not args.pretend:
                      os.rename(f, dest)
  
subject: Fix error when already renamed