For a Django middleware class, how can process_request work just fine, but process_exception not be calls?

Question

I've created my own middleware class in Django that was working just fine until recently. The strange thing is that process_request still gets called just fine, but even when the response is 500 - internal server error, process_exception is not called at all. Why?

It makes no difference whether I declare my middleware class as the first or the last entry in the list of installed middleware in the settings file.

Answer 1

The process_exception only gets invoked when the view raises an Exception. As it says in the comment:

If the view raised an exception, run it through exception middleware, and if the exception middleware returns a response, use that. Otherwise, reraise the exception.

Exceptions raised by misconfiguration, importing error, process_request and process_view cannot be caught and feed to process_exception handlers.

To test whether your process_exception works, raise an Exception in the view after you ensure it works well.

There is not direct relationship between process_request and process_exception. They are handlers for different purposes and get invoked at different stages. Any Exception been raised after the process_request that executed successfully and before the view, will not be caught and processed by process_exception as said.

Answer 2

As per the documentation for process_exception,

process_exception(self, request, exception) takes an HttpRequest object, an Exception object raised by the view function as arguments and returns an HttpResponseobject as response. So, it will not be called when the code raises a 500 error (an HttpResponse object). The process_exception will be called only for uncaught exceptions in the views.