code: def _render_final(self, render_func, *context, **kwargs):
          
          stack = ContextStack.create(*context, **kwargs)
          self._context = stack
  
          engine = self._make_render_engine()
  
          return render_func(engine, stack)
docs: Arguments:
  
            render_func: a function that accepts a RenderEngine and ContextStack
              instance and returns a template rendering as a unicode string.