Can a Jinja variable's scope extend beyond in an inner block?

Question

I have the following Jinja template:

{% set mybool = False %}
{% for thing in things %}
    

        

            {%          


        
                      

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Answer 1

You can solve your problem using this hack (without extensions):

import jinja2

env = jinja2.Environment()
print env.from_string("""
{% set mybool = [False] %}
{% for thing in things %}
    <div class='indent1'>
        <ul>
            {% if current_user %}
              {% if current_user.username == thing['created_by']['username'] %}
                {% set _ = mybool.append(not mybool.pop()) %}
                <li>mybool: {{ mybool[0] }}</li> <!-- prints True -->
                <li><a href='#'>Edit</a></li>
              {% endif %}
            {% endif %}
            <li>Flag</li>
        </ul>
    </div>
    <hr />
{% endfor %}

{% if not mybool[0] %}
    <!-- always prints this -->
    <p>mybool is false!</p>
{% else %}
  <p>mybool is true!</p>
{% endif %}
""").render(current_user={'username':'me'},things=[{'created_by':{'username':'me'}},{'created_by':{'username':'you'}}])

Answer 2

One way around this limitation is to enable the "do" expression-statement extension and use an array instead of boolean:

{% set exists = [] %}
{% for i in range(5) %}
      {% if True %}
          {% do exists.append(1) %}
      {% endif %}
{% endfor %}
{% if exists %}
    <!-- exists is true -->
{% endif %}

To enable Jinja's "do" expression-statement extension: e = jinja2.Environment(extensions=["jinja2.ext.do",])

Answer 3

Answer to a related question: I wanted to have a global counter of the number of times I entered a certain if-block in the template, and ended up with the below.

At the top of the template:

{% set counter = ['1'] %}

In the if-block I want to count:

{% if counter.append('1') %}{% endif %}

When displaying the count:

{{ counter|length }}

The string '1' can be replaced with any string or digit, I believe. It is still a hack, but not a very large one.

Answer 4

Found this great article that describes a little hack. It's not possible to change value of a jinja variable in a different scope, but it's possible to modify a global dictionary values:

# works because dictionary pointer cannot change, but entries can 

{% set users = ['alice','bob','eve'] %} 
{% set foundUser = { 'flag': False } %} 

initial-check-on-global-foundUser: 
  cmd.run: 
    name: echo initial foundUser = {{foundUser.flag}} 

{% for user in users %} 
{%- if user == "bob" %} 
{%-   if foundUser.update({'flag':True}) %}{%- endif %} 
{%- endif %} 
echo-for-{{user}}: 
  cmd.run: 
    name: echo my name is {{user}}, has bob been found? {{foundUser.flag}} 
{% endfor %} 

final-check-on-global-foundUser: 
  cmd.run: 
    name: echo final foundUser = {{foundUser.flag}}

I've also found very helpful this syntax to set the value without actually using set:

{%-   if foundUser.update({'flag':True}) %}{%- endif %} 

It actually checks the result of an update operation on a dictionary (note to self).

Answer 5

Here's the general case for anyone wanting to use the namespace() object to have a variable persist outside of a for loop.

{% set accumulator = namespace(total=0) %}
{% for i in range(0,3) %}
    {% set accumulator.total = i + accumulator.total %}
    {{accumulator.total}}
 {% endfor %}`          {# 0 1 3 #}
 {{accumulator.total}}  {# 3 (accumulator.total persisted past the end of the loop) #}

Answer 6

Update 2018

As of Jinja 2.10 (8th Nov 2017) there is a namespace() object to address this particular problem. See the official Assignments documentation for more details and an example; the class documentation then illustrates how to assign several values to a namespace.