Bug in django\forms\models.py in _construct_form, line 593?

[Piotr Gosławski]

Hi,

when using UpdateView with formset (inlineformset_factory), I randomly got KeyError (page works, refresh, error, refresh, works, ...)

Django Version:     1.7
Exception Type:     KeyError
Exception Value:     0
Exception Location:     ...\django\forms\models.py in _construct_form, line 593
Python Version:     3.4.0

I looked up django source and found:

    except IndexError:
        pass

I thought it was possibly caused by some changes in python 3.x, so I just changed it to

    except (IndexError, KeyError):
        pass

and it seems to work, but I want to make sure I'm not sweeping something else under the rug.
So... am I?

[Tim Graham]

Hi Piotr,

What you've provided is a bit short on details for us to tell. Have you tried searching Trac for a similar issue? "Is this a bug?" questions should usually be asked on the django-users mailing list. A minimal project we can use to reproduce the error is really helpful. If you think it's a Python 3 issue, then see if you can reproduce the issue on Python 2.

Tim

[Piotr Gosławski]

My project is not python 2 compatibile so I've tried to create a minimal project that would reproduce the error, but failed to do so. Turned out the view throwing KeyError was not the problem, at least not by itself. I went back to the original project and started poking at it. Finally I've noticed that the problem doesn't occur until I visit the page associated with another view. So basically view1 was breaking the worker process in such a weird way, that view2 (the one with formset) started throwing KeyError exception. All the other views were not affected. After restarting the server it worked again unil I visited view1.

Refreshing the page was only making it apear random because I had multiple worker processes. After changing number of processes to 1 it was more clear what was happening. Problem occured on Apache with mod_wsgi and uWSGI. It was also appearing on django's devserver, but stopped and I have no idea why.

I then started looking at view1 (based on CreateView) and commented out this method (just taking a long shot):

    def get_initial(self):
        self.initial.update({
            'start_time':datetime.datetime.utcnow().replace(tzinfo=utc) + datetime.timedelta(seconds = 30),
            'end_time':datetime.datetime.utcnow().replace(tzinfo=utc) + datetime.timedelta(minutes = 60),
        })
        return self.initial.copy()

The problem disappeared, but I don't really understand why.
Is there something wrong with the code above?
What kind of sorcery is this?

[Josh Smeaton]

At this point I think you're in the realm of django-users. This is probably a bug in user code rather than django, and you'll get better help from the django-users mailing list or IRC. At a guess the issue may be related to your views not being threadsafe, so you should show your entire view, and how you plug that view into your urlconf.

Regards,