CODEWITHSUNDEEP
pythonflaskjinja2
Sergey Potekhin
Sergey Potekhin

Reputation: 701

Print count before and after Jinja loop

I want to count the number of items in a list that have a specific value and print this count before and after I loop over the items. I tried the following:

{% set counter = [] %}
Counter : {{ counter|length }}

{% for i in array %}
    {% if i['maybe_true'] %}
        {% if counter.append('1') %}{% endif %}
    {% endif %}
{% endfor %}

Counter : {{ counter|length }}

Rendering this produces different values before and after, as expected.

Counter : 0
Counter : 100

Is it possible to get 100 before the loop too?

Upvotes: 1

Views: 910

Answers (1)

davidism
davidism

Reputation: 127180

To your direct question: no, you can't render a variable before you calculate it.

Use a selectattr filter. It returns a generator, so use the list filter before using length.

{{ array|selectattr('maybe_true')|list|length }}

If your actual code is more complex than this, consider moving the logic to Python then sending the processed data to the template.

true_items = [i for i in array if i.maybe_true]
return render_template('index.html', array=array, true_items=true_items)

{{ true_items|length }}
{% for i in array %}
    ...
{% endfor %}
{{ true_items|length }}

Upvotes: 4

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