Best Practice for forms.Form.clean

[Simon Meers]

​https://docs.djangoproject.com/en/dev/ref/forms/validation/#cleaning-and-validating-fields-that-depend-on-each-other

I would advocate changing the example from:

    def clean(self):
        cleaned_data = self.cleaned_data
        # ...

to

    def clean(self):
        cleaned_data = super(ContactForm, self).clean()
        # ...

for the sake of painless form inheritance. Any opposition?

[Simon Meers]

Though I guess it might be helpful to add explanation that the base forms.Form.clean method simply returns self.cleaned_data. I'm wary of complicating things though.

[Julien Phalip]

Calling super() is probably good practice, however if we change the code sample, then the documentation around it should also be modified since it refers to self.cleaned_data.

Playing the devil's advocate, though, I'm not sure that this change would add much value in that part of the documentation. I'm wary it could be slightly confusing for beginners. Also it feels that by the time someone gets to deal with form inheritance, then they're not beginners any more and therefore should already know better about how to use super().

I don't feel strong enough either way so I'll let someone else intervene to triage this ticket :)

[Karen Tracey]

I think it's worth changing to use super(). For a ModelForm, you need to call the superclass clean() in order to get uniqueness checking done. Yes, we note that in the ModelForm doc, but I think it is often missed. Having the clean() example (even if it's a plain form clean) show the best practice makes sense to me.

[Preston Holmes]

I would add a very short note about why the call to super - "to maintain validation logic in the parent classes, use super to call the parent's clean method"

[Simon Meers]

Added documentation note

[Jannis Leidel]

In [17433]:

Fixed #17182 -- Changed best practice documentation for Form.clean to use super() instead of relying on self.cleaned_data. Thanks, DrMeers.