Check if an array is not empty in Jinja2

Question

I need to check if the variable texts is defined or not in index.html.

If the variable is defined and not empty then I should render the loop. Otherwise, I want to show the error message {{error}}.

Basically this in PHP

if (isset($texts) && !empty($texts)) {
    for () { ... }
}
else {
    print $error;
}

index.html

{% for text in texts %} 
    <div>{{error}}</div>
    <div class="post">
        <div class="post-title">{{text.subject}}</div>
        <pre class="post-content">{{text.content}}</pre>
    </div>
{% endfor %}

How do I say this in jinja2?

score 71 · Answer 1 · edited May 23 '17 at 11:46

71

I think your best bet is a combination of defined() check along with looking at the length of the array via length() function:

{% if texts is defined and texts|length > 0 %}
    ...
{% endif %}

edited May 23 '17 at 11:46

Community

1
1

answered Jul 25 '16 at 17:19

andyfeller

905
1
7
12

13

`texts|length > 0` is equivalent to `texts` -- an empty list in a boolean test evaluates to `false`. – Davor Cubranic Jan 26 '17 at 22:15

phs · Answer 2 · 2018-01-24T02:12:59.430

To test for presence ("defined-ness"?), use is defined.

To test that a present list is not empty, use the list itself as the condition.

While it doesn't seem to apply to your example, this form of the emptiness check is useful if you need something other than a loop.

An artificial example might be

{% if (texts is defined) and texts %}
    The first text is {{ texts[0] }}
{% else %}
    Error!
{% endif %}

score 31 · Accepted Answer · answered May 08 '12 at 18:06

31

Take a look at the documentation of Jinja2 defined(): http://jinja.pocoo.org/docs/templates/#defined

{% if variable is defined %}
    value of variable: {{ variable }}
{% else %}
    variable is not defined
{% endif %}

Is it clear enough? In your case it could look like this:

{% if texts is defined %}
    {% for text in texts %} 
        <div>{{ error }}</div>
        <div class="post">
            <div class="post-title">{{ text.subject }}</div>
            <pre class="post-content">{{ text.content }}</pre>
        </div>
    {% endfor %}
{% else %}
    Error!
{% endif %}

answered May 08 '12 at 18:06

Tadeck

132,510
28
152
198

80

This misses the edge case of a defined array that is empty, which should also be an error, according to the original question. – Andrew Sep 16 '15 at 00:53
1

@Andrew Do you know how to fix this edge case? – Patrick Mutuku Jun 03 '18 at 11:56
5

@PatrickMutuku Case of empty but defined array can be handled by {% if texts %} – yeaske Nov 20 '18 at 19:09

score 13 · Answer 4 · answered Apr 07 '17 at 14:34

As mentioned in the documentation, you could also write:

{% for text in texts %}
    <div class="post">
        <div class="post-title">{{text.subject}}</div>
        <pre class="post-content">{{text.content}}</pre>
    </div>
{% else %}
    <div>{{ error }}</div>
{% endfor %}

It handles both the case where texts is undefined, and the case where texts is empty.

score 8 · Answer 5 · answered Aug 10 '18 at 22:16

8

This is a neat and simple solution that worked well for me!

{% if texts is defined and texts[0] is defined %}
    ...
{% endif %}

answered Aug 10 '18 at 22:16

sonictolfa

81
1
2

score 3 · Answer 6 · answered Jun 09 '16 at 23:42

It's possible that texts could be defined but contain a single list element which is an empty string; For example:

texts = ['']

In this case, testing if texts is defined will produce a true result so you should test the first element instead:

{% if texts[0] != '' %}
    ..code here..
{% endif %}

You might also want to combine that with the |length filter to make sure it only has one element.

score 1 · Answer 7 · answered May 06 '22 at 18:12

1

This worked for me when working with the UPS API where if there is only one object in a parent object the child is just an object, but when there is more than one child it's a array of objects.

{% if texts[0] %}
    ..code here..
{% endif %}

answered May 06 '22 at 18:12

Erich Wehrmann

464
2
11

score 0 · Answer 8 · edited Dec 28 '20 at 09:34

This is what worked for my use case in my Django app:

I needed to pass a queryset as context to an html template and display the block only if the queryset had values

Queryset:

events = Event.objects.filter(schedule_end__gte=date.today()).order_by('-created_at')

Passed context dictionary as follows:

{ "events" : events }

HTML template

{% if events %}
  <h3>Upcoming Events</h3>
  <ul>
    {% for event in events %}
    <li><h4>{{ event.title }}</h4></li>
    {% endfor %}
  </ul>
{% endif %}

score 0 · Answer 9 · answered Oct 03 '21 at 10:27

0

This works for me ( But I make sure to return an empty array [] and not None if its empty )

{% if array  %}

   <table class="table">
       ...
   </table>

{% endif %}

answered Oct 03 '21 at 10:27

Am Ben

89
5

score 0 · Answer 10 · answered Aug 01 '22 at 08:37

We can check if array is not empty by writing below jinja code. where the content2 is an array defined under py file. @app.route("/<name>") def home(name): return render_template("index.html", content=name, content2=[])

{% if content2 %}
<div>
    <h2>Array elements are available</h2>
    {% for con2 in content2 %}
        <p> {{con2}} </p>
    {% endfor %}
</div>
{% endif %}

Thanks

Check if an array is not empty in Jinja2

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