Django: Display error message passed by Http404("msg") in custom 404 error handler

Using django 1.11, I have defined a custom 404 handler, by writing in my main URLs.py:

handler404 = 'myApp.views.myError'

The function myError() looks like this:

def myError(request):
    #errorMsg=request.error_404_message
    return render(request,'404.html')

This function works when I call raise Http404("My msg"). However, when I try to get the message passed by the Http404 call (see commented section in myError), my code crashes:

Server Error (500)

How can I then get the error message? I read a lot of questions about it like this one, but most answers refer to getting the message in the html file and not in a custom python error handler function.

EDIT: The problem is, that I cannot see the debug page, because the error obviously only occurs when myError() is called and this happens only, if debug=False in the settings.

The request does not have a error_404_message attribute by default, so request.error_404_message will give you an error.

The answer you linked to sets it as an attribute, but I do not see why you would want to do this in Django 1.9+, since you already have access to the exception in the view.

The signature of your custom view should be:

def myError(request, exception, template_name='404.html'):
    ...

You now have access to exception. You can look at the default page not found view to how it extracts the message from the exception.