code: def extract(self, filename, tu):
          
          it = tu.get_tokens(extent=tu.get_extent(filename, (0, int(os.stat(filename).st_size))))
  
          while True:
              try:
                  self.extract_loop(it)
              except StopIteration:
                  break
docs: extract extracts comments from a translation unit for a given file by
          iterating over all the tokens in the TU, locating the COMMENT tokens and
          finding out to which cursors the comments semantically belong.