🥷 Jinja

Jinja is a template engine, which allows you to generate text from a template.

Installation

Jinja2 is the version compatible with python3. You can install using pip:

pip install Jinja2

Basic Usage

With Jinja you provide a template file with variables that should be filled in. You load this file and then ‘render’ these variables.

Basic Load and Rendering Example

from jinja2 import Environment, FileSystemLoader

name = "jinja"
environment = Environment(loader=FileSystemLoader("templates/"))
template = environment.get_template("message.txt")

# returns rendered template as a string
content = template.render(name=name)

print(content)

Example template file

Hello, my name is {{ name }}.

Comments

Example of Jinja Comment

{# This is a comment #}

Flow Control

if statements

Example if statement

{% if score < 80 %}
You FAILED
{% else %}
You PASSED
{% endif %}

for loops

Example using Jinja for loop

{% for student in students %}
Hello, my name is {{ student }}
{% endfor %}

Nesting templates

As you get more templates, you might want to keep common code in the same place. You can use Jinja’s template inheritance.

Example base template

Hello my name is {{ name }}.

{% block age %} By default my age is {{ age }} {% endblock age %}

Example child template

{% extends "base.template" %}

{% block age %} My new age is {{ age }} {% endblock age %}

If the block age is not given in the overriding template, then the content from the default template will be used.

Including Templates

You are also able to include a whole other template in another template.

Note

Template files which are meant to be included should be prefixed with an underscore in their name.

Example of Jinja include

{% include "_other.template" %}

Some more words.

Whitespace

You need take care about where Jinja will add in whitespace.

Example template

Hello
{# Just a comment #}
You

Produced text

Hello

You

There are a few ways you can avoid this.

1. Enable trim_blocks and lstrip_blocks rendering options

2. Use a - at the start or end of a block. e.g. {% if var == "1" -%}

Built-in Filters

You can see a list of built-in filters here: https://jinja.palletsprojects.com/en/3.1.x/templates/#builtin-filters You can apply a filter by using the pipe symbol |.

Example Jinja filter

First name: {{ first_name | capitalize }}

Example chaining filters

{{ scraped_acl | first | trim }}

Jinja allows you to write your own filters too. These are basically just python functions. See https://ttl255.com/jinja2-tutorial-part-4-template-filters/#:~:text=on%20our%20list.-,Writing%20Your%20Own%20Filters,-As%20I%20already for more info.

Macros

Macros are nice for creating re-usable components.

Example Macros

{% macro banner() -%}
===========================================
|   This device is property of BigCorpCo  |
|   Unauthorized access is unauthorized   |
|  Unless you're authorized to access it  |
|  In which case play nice and stay safe  |
===========================================
{% endmacro -%}

{{ banner() }}

Example output

===========================================
|   This device is property of BigCorpCo  |
|   Unauthorized access is unauthorized   |
|  Unless you're authorized to access it  |
|  In which case play nice and stay safe  |
===========================================

You are also able to pass arguments to macro calls.

Example with arguments

{% macro def_if_desc(if_role) -%}
Unused port, dedicated to {{ if_role }} devices
{%- endmacro -%}

Macros are similar to python function in that they also can have args and kwargs.

Macros in separate file

You can store macros in a separate file and import them into your file as needed.

For example, to import: {% import 'macros.file' as macros -%}. You can access a macro by using macro.<macro_name>.