Jinja2 extends not working?

StackOverflow https://stackoverflow.com/questions/23139165

  •  05-07-2023
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Question

This is my base.html:

<html>
    <head>
        {% block head %}
        {% endblock %}
   </head>
    <body>
        {% block body %}
        {% endblock %}
    </body>
</html>

This is my meta.html:

{% extends 'templates/base.html' %}
{% block head %}

{% if page == 'index' %}
<meta name="mysite.com" content="{{page}}"></meta>
{% else %}
<meta name="mysite.com" content="other page"></meta>

{% endblock %}

This is my index.html:

{% extends 'templates/base.html' %}

{% block body %}
......
{% endblock %}

This is my view:

@view_config(route_name='index', renderer='templates/index.html', permission='view')
def index(request):
    return dict(page="index")

Extending the body works, but the meta tags are not showing up at all. What am I doing wrong?

Was it helpful?

Solution

As per Jinja2 documentation on extends, "The extends tag can be used to extend a template from another one. You can have multiple of them in a file but only one of them may be executed at the time."

When you load index.html from your view, the templating engine assesses index.html. It sees {% extends 'templates/base.html' %} in index.html and uses the blocks within index.html to replace same-name blocks of the parent/extended template (base.html).

So index.html says to use base.html as the skeleton template, but to replace {% block body %} in the parent (base.html) with its own {% block body %}.

Nowhere in this instruction (neither in base.html, nor index.html, nor the view code) does meta.html get mentioned. The templating engine isn't analyzing all the templates in your directory structure to see how it can plug things in. It is only using your explicit directives.

To be explicit about using meta.html, you can use the include directive (documentation found here) in base.html. Your base.html would then look like this:

<html>
    <head>
        {% include 'templates/meta.html' %}
        {% block head %}
        {% endblock %}
   </head>
    <body>
        {% block body %}
        {% endblock %}
    </body>
</html>

This would pull in meta.html and replace the same-name blocks of the skeleton (base.html) with the ones that were retrieved from the included template (meta.html).

In addition, the extends statement within meta.html needs to be removed, so it doesn't create a circular template inclusion.

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