Python Tutorial
Django Template Tags
Tags use percent braces. They control logic, URLs, static files, and template inheritance — they do not print a value by themselves.
Tag vs Variable
| Syntax | Purpose |
|---|---|
{{ name }} | Output a value |
{% tag %} | Run a command (if, for, url, include) |
url Tag
Build a link from a URL name instead of a hard-coded path:
<a href="{% url 'members' %}">All members</a>
<a href="{% url 'details' id=member.id %}">Details</a>extends and block
A base layout with holes that child templates fill:
<!-- templates/master.html -->
<!DOCTYPE html>
<html>
<body>
<nav>Members club</nav>
{% block content %}{% endblock %}
</body>
</html><!-- members/templates/members/all.html -->
{% extends "master.html" %}
{% block content %}
<h1>Members</h1>
{% endblock %}csrf_token
Every POST form must include this tag so Django accepts the request:
<form method="post">
{% csrf_token %}
...
</form>Comments
{# This does not appear in the HTML source #}📘 Real-World Deep Dive
Knowing <strong>Django Tags (Django)</strong> well is what turns Django from a curiosity into a daily tool — you'll reach for it in nearly every real project.
Real-Life Scenario
An end-to-end usage of Django Tags that you'd actually see in a data pipeline or analytics notebook.
Real-Life Example
# myapp/templatetags/formatting.py
from django import template
register = template.Library()
@register.filter
def money(value):
return f"${value:,.2f}"
# Template:
# {{ amount|money }}Expected Output
(no output)Common mistakes
- Forgetting to call
.save()on a model instance after mutation silently persists nothing. - Reading every row with
Model.objects.all()on a 1 M-row table OOMs the worker — use.iterator()for streaming. - Queries inside loops produce N+1 problems — pull related rows with
select_related/prefetch_related. - Treating Django Tags as a black box without reading the docs — the API has subtle defaults that bite when you scale.
🚀 Performance & Best Practices
- Add database indexes (
db_index=TrueorMeta.indexes) on columns used infilter. - Use
cache_pageon read-heavy views and setCONN_MAX_AGEto keep DB connections warm. - Generate migrations with
python manage.py makemigrations --dry-run --verbosity 3and review before committing. - When working with Django, prefer vectorised / batched operations over Python loops.
🧪 Try It Yourself
- Reproduce the snippet on a representative slice of your own data.
- Profile the snippet with
cProfileortimeitand find the single biggest improvement. - Generalise the snippet into a small, reusable function you can drop into future projects.