code: def get_identifier(self):
          
          if 'disqus_identifier' in self.options:
              return self.options['disqus_identifier']
  
          title_nodes = self.state.document.traverse(nodes.title)
          if not title_nodes:
              raise DisqusError('No title nodes found in document, cannot derive disqus_identifier config value.')
          return title_nodes[0].astext()
docs: Validate and returns disqus_identifier option value.
  
          :returns: disqus_identifier config value.
          :rtype: str