code: def _is_variable_extends(extend_node):
      
      if django.VERSION < (1, 4):
          return extend_node.parent_name_expr  # Django 1.3
      else:
          # The FilterExpression.var can be either a string, or Variable object.
          return not isinstance(extend_node.parent_name.var, six.string_types)
docs: Check whether an ``{% extends variable %}`` is used in the template.
  
      :type extend_node: ExtendsNode