Well, Russ, you asked for suggestions, so here's a couple half-hearted
attempts.
Perhaps we could allow for if clauses in the with block or vice-versa? It
could be argued that it would reduce readability and/or induce confusion
with conditional expressions[0], and I would have to agree.
{% with my_bonnet.bees as bees if my_bonnet.bees %}
{# could be confused with conditional expressions #}
<ul class="bee list">
{% for bee in bees %}
<li>{{ bee }}</li>
{% endfor %}
</ul>
{% else %}
<span>No bees!</span>
{% endwith %}
----------------------- or -----------------------
{% if my_bonnet.bees with my_bonnet.bees as bees %}
{# seems a bit repetitive, even though explicit is better than implicit #}
<ul class="bee list">
{% for bee in bees %}
<li>{{ bee }}</li>
{% endfor %}
</ul>
{% else %}
<span>No bees!</span>
{% endif %} {# seems counter-intuitive that this isn't the end of a with
block #}
I'm not too keen on either suggestion, but they seem easier to implement
than the book-keeping alternative. Additional ideas would include having a
magic name for if operands (effectively making if's behave like with's by
default) or creating a different tag altogether.
Cheers,
Andre Terra
[0]:
http://docs.python.org/3/reference/expressions.html#conditional-expressions
On Sun, Jun 2, 2013 at 11:36 PM, Russell Keith-Magee <
russ...@keith-magee.com> wrote:
>
> On Mon, Jun 3, 2013 at 5:36 AM, Daniele Procida <dani...@vurt.org> wrote:
>
>> The for ... empty pattern in templates is common and useful: <
>> https://docs.djangoproject.com/en/dev/ref/templates/builtins/#for-empty>
>>
>> But this is another common pattern:
>>
>> {% if my_bonnet.bees %}
>> <ul>
>> {% for bee in my_bonnet.bees %}
>> <li>{{ bee }}
>> ...
>>
>> In other words, we have to check first for items in the iterable before
>> creating a <ul> or whatever other furniture to put them in.
>>
>> The problem here is that my_bonnet.bees gets asked for twice, and it
>> could be my.bonnet(), some very expensive function.
>>
>> One solution is to put everything inside:
>>
>> {% with my_bonnet.bees as bees %}
>>
>> but now:
>>
>> * we've used up a precious level of indentation
>> * we've introduced a new variable in the templates to worry about
>> * it just feels a bit fussy
>>
>> Is this enough of an issue to make it worthwhile implementing some other
>> approach in the template system?
>>
>> This specific use case (i.e., the empty UL/OL) has bothered me in the
> past as well. However, I'm not sure I see an elegant way to.
>
> I'm open to suggestions, but the only way I can see around the problem is
> to put an extra argument on the {% for %} that allows for extra 'wrapper'
> content "if not empty" - something like:
>
> {% for bee in my_bonnet.bees pre="<ul class='beelist'>" post="</ul>"%}
> <li>{{ bee }}<li>
> {% empty %}
> <span>No bees in your bonnet.</span>
> {% endfor %}
>
> But I'm really not sure I like the syntax combining markup into tags
> arguments. Alternatively, add new sub tags to {% for %}:
>
> {% for bee in my_bonnet.bees %}
> {% pre %}
> <ul class='bee list'>
> {% body %}
> <li>{{ bee }}<li>
> {% post %}
> </ul>
> {% empty %}
> <span>No bees in your bonnet.</span>
> {% endfor %}
>
> but that's starting to get verbose, and leaves ambiguous what to do with
> content appearing between the opening {% for %} and the {% pre %}
>
> Any other syntax I can think of requires introducing another indentation
> level. Have you got a specific suggestion for how to address this?
>
> Russ %-)
>
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