Learning Python3 Flask Part 2

Html and Jinja

Posted by Riino on July 6, 2020 Python Flask Server Web html

Web Source Structure

Remember our repo folder structure?

  │  ├─YourFlaskApp
  │  │  ├─static
  │  │  │  ├─css
  │  │  │  ├─img
  │  │  │  └─js
  │  │  └─templates
  │  │     └─layout
  │  ├─ __init__.py
  │  └─ views.py
  │	└─YourData.csv

Generally we use a static folder to hold all the static sources like css file, javascript file, because it’s the default name of flask when running:

app = Flask(__name__)

And noticed that we can handle the request in views.py, to return a html in templates folder, we shall use:

def target():
    page_name = "CUSTOM VARIABLE"
    return render_template('loading.html', messager_data=page_name)

Via render_template method, flask will try to find corresponding html file in templates, and @app.route will mark this function as a request handler , which is in control layer. The extra messager_data is a usable variable in Jinja, we will talk about this later.

Here, we noticed that html file and css/js files are not in same folder, which means we need to use some approach to let our html file find the static folder. Because if we use path directly, html can not find them for there’s only a templates folder in its sight.


Jinja is the solutions for all the issues above, like Liquid, jinja use embedded syntax in html to mark Variables and Function, for example, we should use this to put our css and javascript path:

  href="{{ url_for('static', filename='css/home.css') }}"

Here we use a ** format to mark that this is a jinja language, and the template engine will run usl_for method to get the correct path.

    src="{{ url_for('static', filename='js/riinosite/jquery.js') }}"

But, the most powerful feature of jinja is template, there’s two modes, import and extend, where the former has less support, but if you come from Liquid, you will be much more familiar with import.


Import means if you put any html file in /template, you can use them via import in another html, but to add path is not supported, for example, if you have _head.html, _footer.html, and _header.html , you can use them in your index.html like:

<!DOCTYPE html>
{% include "_head.html" %}
{% include "_header.html" %}
<!--Your Content-->
{% include "_footer.html" %}

But you can do like “include ”/layout/_footer.html”.


Extend is much more common in jinja, noticed that the html above can be a good template for building other pages, so we can mark our content part as the ‘extendable block’ like:

<!DOCTYPE html>
{% include "_head.html" %}
{% include "_header.html" %}
<section class="home-message ">
    {% block content %}
    {% endblock %}
{% include "_footer.html" %}

Here the block marks this html as a template, to use this template, we can do like :

{% extends "layout/fullscreen_layout.html" %}
 {% block content %}
 <!--Your Content-->
 {% endblock %}

Noticed that we can use a path now, like layout/yourtemplate.html


Now come back to our control function:

def target():
    page_name = "CUSTOM VARIABLE"
    return render_template('loading.html', messager_data=page_name)

Noticed that we put a variable here, so we can use it in jinja:


And if the variable is a list or a dictionary, we can use:

 {% for element in list %}
 {% endfor %}

Also, we can init own variable in jinja, in jinja we use set, this is the most significant difference between jinja and liquid, the latter use assign, except this, the code can almost be copied and run directly from liquid to jinja.