On Sun, Nov 3, 2013 at 9:57 PM, Emanuele Bertoldi <
[email protected]> wrote:
> I've opened a ticket (#21370) with a proposal for the *inclusion of a
> generic "getter" filter* in the built-in library.
>
> *Why?*
>
> Well, because at the moment Django's template system really lacks of
> support for retrieving data from existing context variables in all the
> cases in which the name of the attribute we need is determined at execution
> time.
>
It's worth pointing out that this is something the Django core team has
historically rejected, on the basis that it's a slippery slope from here to
turning Django's template language into a fully featured programming
language. So -- fair warning -- the default answer here is going to be
"No"; it's going to take some convincing to flip that position.
However, I will admit that this is a use case for which I have some
sympathy. Cross-cutting arrays of data is one of those things that is a lot
more complex to do in the context than it would be to do using a simple
lookup in a template.
Formally, I'm probably +0.1 :-)
> *Syntax:*
>
> {{ object|get:attr_name }}
>
> Of course the idea is to add a multi-purpose filter which covers different
> use cases (model instances, arbitrary objects, dicts, lists, tuples, etc.)
>
*IF* we are to add this, I'd be inclined to do this as a primitive of the
template language itself, rather than as a template filter. This is a
fundamental concept in context lookup, not a data transformation (which is
what filters generally represent).
The minimal syntactic solution would be to use the colon operator to denote
arguments in the same way as it does for filters:
{{ object:attr_name }}
or, by introducing square brackets as parseable symbols in the template
language:
{{ object[attr_name] }}
The latter has the benefit of being compatible with Jinja syntax; the
downside is that Django templates starts to look even more like a
programming language.
Yours,
Russ Magee %-)
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