code: def _replace_file(path, content):
    
    if os.path.exists(path):
      with open(path, 'r') as f:
        if content == f.read():
          print("Not overwriting {} because it is unchanged".format(path), file=sys.stderr)
          return
  
    with open(path, 'w') as f:
      f.write(content)
docs: Writes a file if it doesn't already exist with the same content.
  
    This is useful because cargo uses timestamps to decide whether to compile things.