#31877: TemplateView.get_context_data()'s kwargs returns SimpleLazyObjects that
causes a crash when filtering.
-------------------------------------+-------------------------------------
Reporter: Tim L. White | Owner: Adam
| (Chainz) Johnson
Type: Bug | Status: new
Component: Generic views | Version: 3.1
Severity: Release blocker | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Tom Forbes):
There isn't really a general purpose way of wrapping primitive/arbitrary
types like this in Python that won't hit some corner cases. You can make
an object appear to be a duck by adapting it's quacking dynamically (i.e
`wrapt.ObjectProxy`), but if someone looks close enough they can always
see that it's actually dog. And on the whole that's a good thing, IMO.
Our use of `kwargs` makes this harder as we lose the ability to construct
a container that can trigger the deprecation warning which would be the
typical easy approach. There is no way to control what lands on the other
side of `get_context_data()` (it's always a plain kwargs dict), and there
is no way to construct a wrapper value that looks _exactly_ like the value
it's wrapping.
That basically leaves only "crazy" approaches, some of which are fun to
consider but none of which are suitable. Here's one that uses `settrace()`
to do what we need:
{{{
import sys
class DeprecatedWrapper(dict):
def __getitem__(self, key):
warnings.warn("stop right there, scoundrel!")
return super().__getitem__(key)
def wrap_kwargs(frame, *args):
frame['kwargs'] = DeprecatedWrapper(frame['kwargs'])
sys.settrace(None)
class TemplateView(...):
def get(...):
...
sys.settrace(wrap_kwargs)
context = self.get_context_data(**context_kwargs)
return self.render_to_response(context)
}}}
Given these issues, I'm not sure if we can go ahead with deprecating this.
--
Ticket URL: <https://code.djangoproject.com/ticket/31877#comment:12>
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