id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
28244	Exceptions derived from BaseException instead of Exception are not caught by convert_exception_to_response()	alexpirine	nobody	"Hello,

[https://docs.python.org/3/library/exceptions.html#built-in-exceptions Python documentation] states:

  In Python, all exceptions must be instances of a class that derives from `BaseException`.

Deriving exceptions from `Exception` is a recommendation, but does not seem to be an absolute requirement:

  programmers are encouraged to derive new exceptions from the `Exception` class or one of its subclasses, and not from `BaseException`.

So, if `BaseException` is used instead of `Exception`, Django's [https://github.com/django/django/blob/master/django/core/handlers/exception.py#L36 convert_exception_to_response] doesn't catch it, and crashes instead:

{{{
#!python
def convert_exception_to_response(get_response):
    @wraps(get_response)
    def inner(request):
        try:
            response = get_response(request)
        except Exception as exc:
            response = response_for_exception(request, exc)
        return response
    return inner
}}}

If you run it on gunicorn with nginx, which is often the case, you will see ''upstream prematurely closed connection while reading response header from upstream'' errors, without any additional info, and without any logs whatsoever, even if you properly configured a logging system.

Only running `manage.py runserver` will display the full stack trace:

{{{
Traceback (most recent call last):
  File ""…/python3.6/wsgiref/handlers.py"", line 137, in run
    self.result = application(self.environ, self.start_response)
  File ""…/django/contrib/staticfiles/handlers.py"", line 63, in __call__
    return self.application(environ, start_response)
  File ""…/django/core/handlers/wsgi.py"", line 157, in __call__
    response = self.get_response(request)
  File ""…/django/core/handlers/base.py"", line 124, in get_response
    response = self._middleware_chain(request)
  File ""…/django/core/handlers/exception.py"", line 41, in inner
    response = get_response(request)
  File ""…/django/utils/deprecation.py"", line 140, in __call__
    response = self.get_response(request)
  File ""…/django/core/handlers/exception.py"", line 41, in inner
    response = get_response(request)
  [… and so on, depending on how much middleware you have …]
  File ""…/django/utils/deprecation.py"", line 140, in __call__
    response = self.get_response(request)
  File ""…/django/core/handlers/exception.py"", line 41, in inner
    response = get_response(request)
  File ""…/django/core/handlers/base.py"", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File ""…/django/views/decorators/http.py"", line 40, in inner
    return func(request, *args, **kwargs)
  File ""…/your_project/views.py"", line 42, in your_func
    …
your_project.YourErrorInheritedFromBaseException: Your error message
}}}

Of course I fixed my code by inheriting from `Exception`.

But I wonder if catching `BaseException` instead of `Exception` would be a good change?"	Uncategorized	closed	Uncategorized	1.11	Normal	wontfix			Unreviewed	0	0	0	0	0	0