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Jinja2 Template engine

Jinja2 is a template engine for Python.  You can use it when rendering data to web pages.  For every link you visit, you want to show the data with the formatting. By using a template engine we can seperate display logic (html, css) from the actual Python code. Let’s start with an example

Related course
Python Flask: Make Web Apps with Python

Getting started with Jinja2
Create the directories:

  • /app
  • /app/templates

And create the file user.html in /app/templates:

<title><block title %><endblock %></title>
<ul>
<for user in users %>
<li><user></li>
<endfor %></ul>

Then create the code app.py  in /app/app.py:

from flask import Flask, flash, redirect, render_template, request
from random import randint

app = Flask(__name__)

@app.route("/")
def index():
return "Flask App!"

@app.route("/user/")
def hello():

users = [ "Frank", "Steve", "Alice", "Bruce" ]
return render_template(
'user.html', **locals())

if __name__ == "__main__":
app.run(host='0.0.0.0', port=8080)

Finally execute with:

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3
python app.py
* Running on http://0.0.0.0:8080/

You can then open http://127.0.0.1:8080/user/  in your browser. This will output the data formatted according to html:

<caption id=”attachment_1290” align=”alignnone” width=”637”]jinja2 Jinja2 Template Engine Output

About Jinja
A Jinja2 template is simply a text file that does not need to have a specific extension such as .html, .xml.
A template may contain tags and special delimiters:

Delimiters Usage
<… %> Statements
< … >> Expressions to print to the template output
<… #> Comments not included in the template output
# … ## Line Statements

In the example above we have two statements and one expression.  We have not included any comments.

Base template and child templates
A Jinja2 template can extend a base template. On a webpage with many sites you may want these pages look similar.  In /templates/ create a file called base.html with this code:



<block head %>
<link rel="stylesheet" href="style.css">
<title><block title %><endblock %> - My Webpage</title>
<endblock %>
<div id="content"><block content %><endblock %></div>
<div id="footer">
<block footer %>
Copyright 2015 by <a href="https://pythonspot.com/">pythonspot</a>.
<endblock %></div>

We did not set a style.css, but you could set one. Change /templates/user.html to:

<extends "base.html" %>
<block title %>Index<endblock %>
<block head %>
<#123; super() >>
<style type="text/css">
.important <olor: #336699; ><br />
</style>

<endblock %>
<block content %>
<h1>Users</h1>
<p class="important"></p>

<ul>
<for user in users %>
<li><#123; user >></li>
<endfor %></ul>
<endblock %>

Restart the app with:

python app.py
* Running on http://0.0.0.0:8080/

Output:

<caption id=”attachment_1294” align=”alignnone” width=”637”]template jinja Flask Jinja template engine