My proposal to create a new exception

[Victor Porton]

In https://code.djangoproject.com/ticket/31239 I proposed to create QueryDictKeyError derived from MultiValueDictKeyError and raise this exception on a missing parameter in request.GET and request.POST.

It is to be done to handle error in user data easily:

try:
 x = request.GET['x']
except MultiValueDictError:
 return response("Missing user data 'x'", status=404)
try:
 y = request.GET['y']
except MultiValueDictError:
 return response("Missing user data 'y'", status=404)


is much more cumbersome and error-prone than:

def handle_exception(self, exc):
  if isinstance(exc, QueryDictKeyError):
    # It is an unwise assumption that this is necessarily missing HTTP param,
    # but rewriting it in other way would be time consuming (and maybe even more error prone).
    return MyErrorResponse({"code": "PAR_1", "message": "Missing param.", "field": exc.args[0]})

The latter may be added to a base view to handle such errors in the entire project easily.

This handle_exception() could be even integrated into the core of Dajngo to handle such errors automatically without the user writing this code manually repeatedly.

Moreover, the above code is much more maintenable, as no need to change error messages in each and every view, if a user wants to change the error message.

Programming is about automation and we need the task about handling user input errors to be done automatically.

@felixxm claims "Creating a single method to catch and handle all kind of exceptions is error prone."

But the reverse things is true: not handling exception automatically leads to many code errors.

@felixxm's claim as valid as "use CGI instead of Django: using a CMS is error-prone, specify in the code exactly what you want rather to relying to a single method."

If code can be simplified, it needs to be simplified.

Please support my feature request.

[Steven Mapes]

Perhaps I'm totally missing the point and use case for this but is there any reason you are not simply using any of these

if expected_key is not in request.GET:
    return MyErrorResponse(...)

if not request.GET.get("expected_key", None):
    return MyErrorResponse(...)

required = ["one", "two", "three", "four"]
if not all(k in request.GET.keys() for k in required):
    return MyErrorResponse(...)

I've used the latter approach if I have required parameters in a GET/POST and I'm not using forms. I  just adding the check to a base view and having required
be an attribute

[Victor Porton]

Just because your code repeated in each and every form can be eliminated and we can check it all in one place,

shortening code, eliminating duplication, reducing possibilities of errors.

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