def get_page_sentence(self, wikipedia_url,
                        sentence_id):
    """Get the text for a sentence on the given wikipedia page.

    Args:
      wikipedia_url: Url to lookup
      sentence_id: The sentence to retrieve

    Returns:
      The text of the sentence if it exists, None otherwise
    """
    page = (
        self.session.query(WikiPage).filter_by(
            wikipedia_url=wikipedia_url).first())
    if page is None:
      return None
    else:
      page_proto = fever_pb2.WikipediaDump.FromString(page.proto)
      if sentence_id in page_proto.sentences:
        return page_proto.sentences[sentence_id].text
      else:
        return None
Get the text for a sentence on the given wikipedia page.

    Args:
      wikipedia_url: Url to lookup
      sentence_id: The sentence to retrieve

    Returns:
      The text of the sentence if it exists, None otherwise
    
language/serene/wiki_db.py