Template system improvement: "cat" filter, "include" tag with filters

[David Avsajanishvili]

There are two suggestions:

1. Since we have add filter, that adds a value to integer variable, why not implement cat filter, which will concatenate strings? I think, it would be useful for many developers!

2. include tag has two options: template name could be specified either as a quoted string, or as a variable. But for all that template filters cannot be used. It would be nice to allow developers to specify template name more flexibly, for example:

   {% include var_name|lower %}

or even like this (page5_ka.txt):

   {% include "page"|cat:pageid|cat:LANGUAGE_CODE|cat:"_.txt" %}

The diffs attached to the ticket do these things. At the same time, new revision of template system will be fully backwards-compatible with previous.
An only exception is - using quoted strings with quotes inside, like this:

    {% include "a"mysterious"template.txt" %}

Currently, template system accepts this string as a template name with doublequotes inside, while modified - won't. But, IMHO, nobody will name templates this case.

[David Avsajanishvili]

"cat" filter (concatenate argument with value)

[David Avsajanishvili]

"include" tag modified so, it can process template filters

[David Avsajanishvili]

"cat" filter and "include" tag description update in documentation

[dc]

{% include "page"|cat:pageid|cat:LANGUAGE_CODE|cat:"_.txt" %}

I think that's to many logic in template.

[David Avsajanishvili]

I think that's to many logic in template.

Yes, but such usage is only an option available.
Although in some cases it might be useful.
See google-groups:
​http://groups.google.com/group/django-developers/browse_thread/thread/21631ff4141a8db3

[Johannes Dollinger]

The {% include %} fix is a duplicate of #5862 and #5756, and would be fixed by #7806.

The cat filter is definitely useful, I call it concat and use it just like proposed here.

[David Avsajanishvili]

Replying to emulbreh:

The {% include %} fix is a duplicate of #5862 and #5756, and would be fixed by #7806.

Good! Exactly that I have in mind!
Please, take into account this: ​http://code.djangoproject.com/attachment/ticket/5756/5756.3.patch

[(none)]

Milestone post-1.0 deleted

[dc]

See also #11687 which proposes to make 'add' filter more versatile.

[Jacob]

These are both useful features, but both can be implemented externally, and they don't cross the threshold of being widely useful. Thus, they're not a great match to include in Django's core.

Thanks!

[anonymous]

It's hard to objectively assess what the threshold of being widely useful is. Speaking of the "concat" filter, I personally thought it actually crossed that threshold, based my own experience and that of several co-workers...

[Julien Phalip]

That was me in the comment above.