#22510: Form fields cannot have names that are present as attributes on the form
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Reporter: gc@… | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 1.7-beta-2
Severity: Release blocker | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by gcbirzan):
Replying to [comment:2 loic84]:
> At the time I suggested we only allowed shadowing with `None`, @mjtamlyn
convinced me that we should follow normal Python inheritance/shadowing and
I think that was a good decision.
True, but the problem is that the builtin Form fields also have this
property. It's made worse by, for example, media being set by magic via
the previous meta class, so it's set on each of the classes that inherit
from Form.
> I see value in matching as closely as possible the MRO behavior, other
than the fact that `Field` magically remove themselves from the class
(whether shadowed or not), we are pretty good on that front.
>
> Inheritance makes this kind of clash possible, but a single form
couldn't define both a `Field` and an attribute anyway.
>
> To expose a `media=42` attribute like in the test of the proposed patch,
one can set `self.media` in `__init__()`, or ensure that it appears first
in the MRO. By ensuring it appears first in the MRO it won't shadow any
field, and it will not be shadowed itself because fields are removed from
the class.
To be honest, I don't remember why media = 42 is in there, it doesn't
really matter, it happens either way.
As for the proposed solution, with `__init__()` is ugly and, at the very
least, needs documentation explaining that things you don't manually set
might have this effect.
> We document:
>
> {{{
> It's possible to opt-out from a ``Field`` inherited from a parent class
by
> shadowing it. While any non-``Field`` value works for this purpose, it's
> recommended to use ``None`` to make it explicit that a field is being
> nullified.
> }}}
>
> Which is exactly the case described in the test of the proposed patch.
True. But even so, there's another bug that's fixed by my patch.
Reordering the shadowing and collecting means that, if nothing else,
defining media as a field on a form will work, if there's no other
inheritance.
--
Ticket URL: <https://code.djangoproject.com/ticket/22510#comment:3>
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