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List:       cobbler-devel
Subject:    Re: template languages (was: Release plan?)
From:       Stuart Sears <stuart () sjsears ! com>
Date:       2011-08-26 14:22:31
Message-ID: 4E57AC27.3010604 () sjsears ! com
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On 08/26/2011 01:10 PM, James Cammarata wrote:
>> If you like the Django template language (I do :) ), then jinja2 might
>> be an alternative. It was based around the same syntax and extended.
>
> I've been playing with a few, and I really like both mako and jinja2.
> The main problem I see with mako is it's damn near impossible to stop
> people from importing random python modules. I tried some preprocessor
> hooks to strip imports out, but it's messy. Jinja2 is much better, and
> you can enable "line syntax" which makes the syntax more cheetah-like:
>
> {% for foo in bar %}
>    {{ foo }} {# comment that won't show up in the output #}
> {% endfor %}
> {% include "some_other.tmpl" %}
>
> can become:
>
> #for foo in bar:
>    {{ foo }} ## comment that won't show up in the output
> #endfor
> #include "some_other.tmpl"
>
> There is a small issue when you do it this way - it tries to interpret
> any line starting with # as a python commands. I've gotten around that
> by using #: as the character combo to indicate python lines. So it's
> not exactly like cheetah, but it's still very easy to read and write:
>
> #:for i in test:
> # comment will show up
> variable is {{ i }} ## comment won't be output
> #:endfor
> #:include 'test2'
>
> The code to render this is very simple:
>
>    from jinja2 import Environment, FileSystemLoader
>    env = Environment(
>              loader=FileSystemLoader(['/var/lib/cobbler/snippets',]),
>              line_statement_prefix="#:",
>              line_comment_prefix="##")
>
>    template = env.get_template('test')
>    print template.render({'test':[1,2,3]})
>
> Note that the FileSystemLoader() class can take multiple directories,
> so we could easily add the feature allowing multiple snippet
> directories.
>
> So, overall, if I had to pick a templating language today it would be jinja2.
>
>
>> I was considering (in my less-than-copious free time) hacking the
>> templating engine parts to be modular, or attempting to. That would
>> allow the testing of different engines.
>> Dunno how hard that would turn out to be though.
>
> I don't know if it's worth the effort to modularize this - it's
> something we shouldn't be switching out that often. It would make it
> easier to switch out if at some point the new language we choose
> starts slipping on support the way cheetah has, but how likely is
> that?

unlikely, I agree.
The modularization was for me more than anything. I like choice.
I see the cobbler end as a means of defining system (etc) parameters and 
passing them to a templating engine.
I'd quite like the templating engine to be up to me :)

Besides, the more modular the better - the same applies to the (already 
modularised) backends.

cheetah's rather twisted use of the octothorpe has always irked me a little.

Stuart

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