#21765: Contexts cannot be compared for equality.
-------------------------------------+-------------------------------------
Reporter: Keryn Knight | Owner: onjin
<django@…> | Status: new
Type: New feature | Version: master
Component: Template system | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: | Needs documentation: 0
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by Keryn Knight <django@…>):
* status: closed => new
* resolution: fixed =>
Comment:
Re-opening with permission:
The fix as committed is not entirely correct, I don't think, as it only
compares the '''last''' state change of a given context, so comparisons
can incorrectly return as equal if context states drift and then re-align,
for example:
{{{
>>> import django
>>> from django.template import Context
>>> a = Context()
>>> b = Context()
>>> a == b
True
}}}
the above is correct; from here on out, the contexts are continuations of
the above example:
{{{
>>> a.update({'a': 1})
>>> a == b
False
}}}
that's also correct.
{{{
>>> a.update({'c': 3})
>>> b.update({'c': 3})
>>> a == b
True
}}}
This is where the incorrectness appears. They are ''not equal'', but their
last push to the stack was, so they're being treated as equal. Based on
the commit in question (`d97bf2e9c8971764690caaf81a0914bc368d6b02`), the
change would be going from:
{{{
return self.dicts[-1] == other.dicts[-1]
}}}
to
{{{
return self.dicts == other.dicts
}}}
which would at least ensure the rest of the context is taken into account,
though that fix in itself may not be as correct as it should be -- it is
'''strict''' in the sense that the entire history of the contexts being
compared must be aligned, where it should perhaps instead squash the stack
into one dictionary for both sides and compare ''them'' for equality.
(Whether or not strictness is a benefit or problem is probably a DDN, and
like testing equality for context subclasses which differ (or have
different attrs, for things like `RenderContext`) could probably be
tracked in separate tickets, though.)
--
Ticket URL: <https://code.djangoproject.com/ticket/21765#comment:5>
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