handler500 as a Class-based view raises SystemCheckError

[Daniyal Abbasi]

Setting handler500 as a Class-Based view raises the following error which running checks.

$ python manage.py check
SystemCheckError: System check identified some issues:

ERRORS:
?: (urls.E007) The custom handler500 view 'path.to.my.MyView' does not take the correct number of arguments (request).

In my root urls.py, I have the following configuration,

handler404 = MyView.as_view()
handler500 = MyView.as_view()

I believe this is due to the function _check_custom_error_handlers in django/urls/resolver.py. The signature variable in this function is expected to match (request, exception) for all handlers except for handler500 which is expected to have only (request). A positional argument, template_name is also present.

While using class based views, we get two positional arguments (self, request) and then it recieves *args and * *kwargs. The check is permitting other handlers as the number of arguments coincidentally match.

I suggest a fix in the _check_custom_error_handlers which first checks if the handler* are function based or class based, and then it preceed the check with the appropriate number of arguments.