Jinja: Can we get an {% empty %} tag?

[priestc]

Django has this really cool tag called {% empty %}, which lets you do this:

{% for item in list %}
    <tr><td>{{ item }}</td></tr>
{% empty %}
    <tr><td>Nothing to show!</td></tr>
{% endfor %}

which is short for

{% if list %}
    {% for item in list %}
        <tr><td>{{ item }}</td?</tr>
    {% endfor %}
{% else %}
    <tr><td>Nothing to show!</td></tr>
{% endif %}

Since switching to jinja, I have really missed this tag :(

[mitsuhiko]

That already exists. Use {% else %} on a for loop. Unfortunately we had else before Django created empty and renaming it now to match Django semantics is kinda weird.

[priestc]

oh, i see. Maybe put a note of that in the "Switching from other Template Engines" under then django section?

[inactivist]

I don't see this in the switching documentation. It is mentioned in the control structures:for documentation but it would be helpful to have it in the switching doc...

[WloHu]

If list in code is a generator and for and if blocks work in the same way as in Python then the if-for construct doesn't solve the problem because generators are always truthy, plus such construct is less idiomatic than empty block.

I don't know if you can add a flag to check if loop has run, check for NameError: name 'item' is not defined or add helper variable to list(generator) at Jinja level. If not, then the only solutions is to add the empty block or convince Python devs that empty generators should be falsy (to avoid ugly checking by handling StopIteration and "pushing back" popped item).

[mitsuhiko]

The else block in Jinja works like the empty block in Django already. No change is necessary here.