def my_render_callback(response):	return responsefrom django.template.response import TemplateResponsedef my_templateresponse(request):	response =  TemplateResponse(request, 'template.html', {})	response.add_post_render_callback(my_render_callback);	return response

we call add_post_render_callback to register a callback function.

in base.py , get_response 

 

if hasattr(response, 'render') and callable(response.render):                    for middleware_method in self._template_response_middleware:                        response = middleware_method(request, response)                    response = response.render()

The response is a TemplateResponse, the subclass of  SimpleTemplateResponse

 

it has a 'render' function

 

def render(self):        """Renders (thereby finalizing) the content of the response.        If the content has already been rendered, this is a no-op.        Returns the baked response instance.        """        retval = self        if not self._is_rendered:            self.content = self.rendered_content            for post_callback in self._post_render_callbacks:                newretval = post_callback(retval)                if newretval is not None:                    retval = newretval        return retval

需要注意的是这个callback的返回值, 如果 not None, 它的返回值就是我们最后的response,