Introduction

Flask uses the Jinja2 templating engine to render dynamic HTML pages. It lets you embed Python-like expressions directly in your HTML.

Setting Up Templates

Create a folder called templates in your project root. Flask looks there automatically.

Your First Template

Create templates/index.html with the following content.

{{ heading }}

Passing Data from Flask

Use render_template to pass variables to your template.

return render_template("index.html", title="Home", heading="Welcome!")

Control Flow in Templates

Jinja2 supports if statements and for loops.

{% if user %}

Hello, {{ user }}!

{% else %}

Please log in.

{% endif %}

{% for item in items %}

{{ item }}

{% endfor %}

Template Inheritance

Use a base template to avoid repeating HTML across pages.

In base.html, define a block.

{% block content %}{% endblock %}

In child templates, extend and fill the block.

{% extends "base.html" %}

{% block content %}

Page content here

{% endblock %}

Filters

Jinja2 filters transform values inline.

{{ name | upper }}

{{ items | length }}

{{ text | truncate(100) }}