new_contents: # Copyright (c) 2010 The Chromium Authors. All rights reserved.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  import re
  import sys
  
  # A tool to add "#pragma once" lines to files that don't have it yet.
  # Intended usage:
  #   find chrome -name '*.h' -exec  python tools/pragmaonce/pragmaonce.py {} \;
  
  # Some files have absurdly long comments at the top
  NUM_LINES_TO_SCAN_FOR_GUARD = 250
  
  def main(filename):
    f = open(filename)
    lines = f.readlines()
    f.close()
  
    index = -1
    for i in xrange(min(NUM_LINES_TO_SCAN_FOR_GUARD, len(lines) - 1)):
      m1 = re.match(r'^#ifndef ([A-Z_]+)', lines[i])
      m2 = re.match(r'^#define ([A-Z_]+)', lines[i + 1])
      if m1 and m2:
        if m1.group(1) != m2.group(1):
          print 'Skipping', filename, \
                ': Broken include guard (%s, %s)' % (m1.group(1), m2.group(1))
        index = i + 2
        break
  
    if index == -1:
      print 'Skipping', filename, ': no include guard found'
      return
  
    if index < len(lines) and re.match(r'#pragma once', lines[index]):
      # The pragma is already there.
      return
  
    lines.insert(index, "#pragma once\n")
  
    f = open(filename, 'w')
    f.write(''.join(lines))
    f.close()
  
  if __name__ == '__main__':
    if len(sys.argv) != 2:
      print >>sys.stderr, "Usage: %s inputfile" % sys.argv[0]
      sys.exit(1)
    main(sys.argv[1])
  
subject: Add python script that can add "#pragma once" to all our files.