docs: def _find_num_pages(self, url):
      """
      Find the number of pages paginating a genre's letter URL
      """
      def _new_url(i):
        return '{}&page={}#page'.format(url, i)
      i = 0
      j = 2000
      k = (i + j) / 2
      crawler = SeriesCrawler(_new_url(k))
      while i < j:
        ids = crawler.get_ids()
        # If we only find one (we've gone too far)
        if len(ids) == 1:
          # Don't decrement by 1 b/c this could be the last page
          j = k
          k = (i + j) / 2
          crawler.set_url(_new_url(k))
        else:
          i = k + 1
          k = (i + j) / 2
          crawler.set_url(_new_url(k))
      return i