layout_example.html

# child.html
{% extends 'layouts/full_width.html' %}
{% load static filters staticfiles %}

{% with sidebar_width="echo test" %}
    {% block sidebar_wrapper %}
        {{ block.super }}
    {% endblock sidebar_wrapper%}
{% endwith%}

{% block sidebar %}
    {{ block.super }}
    <div>
        sidebar stuff
    </div>
{% endblock %}

#layouts/full_width.html

{% block sidebar_wrapper %}
    ={{ sidebar_width }}=
    {% block sidebar %}{% endblock %}
{% endblock sidebar_wrapper %}