code: def get_node_at_path(query_path, context):
      
      if query_path not in context.query_path_to_node:
          raise AssertionError(
              u'Unable to find SqlNode for query path {} with context {}.'.format(
                  query_path, context))
      node = context.query_path_to_node[query_path]
      return node
docs: Return the SqlNode associated with the query path.