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

Created on 2 Dec 2011 · 5Comments · Source: pallets/jinja

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 :(

Source

priestc

👍3

Most helpful comment

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.

mitsuhiko on 3 Dec 2011

👍8

All 5 comments

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.

mitsuhiko on 3 Dec 2011

👍8

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

priestc on 3 Dec 2011

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

inactivist on 25 Mar 2013

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).