code: def search_for_comment(self, lineno, default=None):
          
          if not self.index:
              self.make_index()
          block = self.index.get(lineno, None)
          text = getattr(block, 'text', default)
          return text
docs: Find the comment block just before the given line number.
  
          Returns None (or the specified default) if there is no such block.