Jinja2: Efficient template engine in Flask applications

Jinja2 is a pure Python-written template engine that provides a Django-like non-XML syntax, while supporting inline expressions and optional sandboxing environments. It is compact, fast and easy to use and is a standalone template engine. Flask is a tiny Python-based web framework that allows you to write web applications quickly and efficiently.

This series of tutorials will explain the basic knowledge of Jinja2 templates from the perspective of Flask. The following section will introduce advanced template topics and learn how to layout templates in a modular and scalable way in Flask-based applications.

This tutorial assumes that you have mastered the basics of Flask and understand the best practices for setting up environments using virtualenv for Python application development.

Installation Pack

Flask comes with Jinja2, so we only need to install Flask. This tutorial series recommends using the development version of Flask, which includes more stable command line support, as well as many other features and improvements.

pip install https://github.com/mitsuhiko/flask/tarball/master

Why do you need a template engine?

In Flask, we can write a complete web application without any third-party template engine. Let's look at a simple example of if, else and {% %} blocks. Update the home.html page as follows:

flask_app/templates/home.html

{% extends 'base.html' %}

{% block container %}
<div class="top-pad">
    {% for id, product in products.items() %}
    <div class="well">
    <h2>
        <a href="http://www.miracleart.cn/link/0bbfd30c6d7efe2fff86061e79c010db'product', key=id) }}">{{product['name']}}</a>
        <small>$ {{ product['price']}}</small>
    </h2>
    </div>
    {% endfor %}
</div>
{% endblock %}

Watch how this template extends the upper filter as shown below:

{% extends 'base.html' %}

{% block container %}
<div class="top-pad">
    {% for id, product in products.items() %}
    <div class="well">
    <h2>
        <a href="http://www.miracleart.cn/link/0bbfd30c6d7efe2fff86061e79c010db'product', key=id) }}">{{product['name']|upper}}</a>
        <small>$ {{ product['price']}}</small>
    </h2>
    </div>
    {% endfor %}
</div>
{% endblock %}

Now, if you run the server, you should notice that the product name is all capitalized.

Summary

In this tutorial, we learned how to use Jinja2 layout template structure in a Flask-based application. We also learned how to use blocks to leverage inheritance in templates.

In the next part of this series, we will learn how to write custom filters, custom context processors, and macros.

This article has been updated and contains contributions from Esther Vaati. Esther is a software developer and contributor to Envato Tuts.

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