Jinja templates: how inPace draws every page

Your plan for these four days

Day	Module	Time
1	Templates, variables, filters and escaping	about 1.5 h
2	Inheritance, includes and macros	about 1.5 h
3	The Environment: globals, filters, i18n	about 1.5 h
4	Testing, performance, security, interview drill	about 1.5 h

Install Jinja (pip install jinja2) and keep inpace/templates/ and the top of inpace/app.py open. inPace has about 50 templates that all extend one base.html.

The syntax

Tag	Does
{{ ... }}	Prints an expression
{% ... %}	A statement: if, for, set, block, macro...
{# ... #}	A comment, never sent to the browser

<h1>{{ course.title }}</h1>
{% if progress.percent >= 100 %}
  <p class="done">Finished!</p>
{% elif progress.percent %}
  <progress value="{{ progress.percent }}" max="100"></progress>
{% else %}
  <p>Not started yet.</p>
{% endif %}

<ul>
{% for m in course.modules %}
  <li class="{{ 'open' if m.open else 'locked' }}">{{ loop.index }}. {{ m.title }}</li>
{% else %}
  <li>This course has no modules.</li>
{% endfor %}
</ul>

• course.title tries the attribute, then course["title"]: dicts and objects look the same in templates.
• loop.index, loop.first, loop.last, loop.length are available in every for.
• for ... else runs when the list is empty.
• A missing variable is Undefined: it prints as empty by default. StrictUndefined makes it an error (great in tests).

Rendering from Python

from jinja2 import Environment, FileSystemLoader, select_autoescape
env = Environment(loader=FileSystemLoader("templates"), autoescape=select_autoescape(["html"]))
html = env.get_template("lesson.html").render(course=c, progress=p)