[FIXED] Jinja2 If ignores boolean value

Issue

I have a Jinja2 template where a variable that resolves as a boolean False is being ignored in an {% if %} statement.

The relevant chunk of the template looks like

{% if user.can_manage_techniques %}j
{% block submenu_items %}
<li class="pure-menu-item"><a href={{ url_for('new_technique') }} class="pure-menu-link">New Technique</a></li>
{% endblock %}
{% endif %}

The user is set in render template as

    return render_template('technique_list.j2',
                            techniques=Technique.find_all(),
                            **state())

with the state being a function that returns a dict[string, object].

The user that is passed to it is set in the __init__ of the object as a variable - so:

    def __init__(self):
        self.can_manage_techniques = False

Even when the can_manage_techniques is false, the list item still renders. How do I make the {% if %} realise that it is false and go to the {% endif %}?

I have also tried == true and sameas true

Solution

I can't reproduce your problem on local with minimal app below:

from flask import Flask, render_template_string
app = Flask(__name__)

@app.route('/')
def hello():
    return render_template_string('''
        {{ can }}
        {% if can %}
            {% block submenu_items %}
                <li class="pure-menu-item">New Technique</li>
            {% endblock %}
        {% endif %}
        ''', can=False)

IMO, the usage is correct, so you may need to check more related code.

I found why this happened after checking your code on GitHub. This issue caused by the template inheritance behavior: In child template, contents outside the block will be skipped.

Since your template is child template, so you need to put the if statements into the block.

Answered By - Grey Li