Django template syntax

• template is a text file. It can generate any text-based format (HTML, XML, CSV, etc.).
• template contains variables , which get replaced with values when the template is evaluated
• template tags control the logic of the template.

template.html

{% extends "base_generic.html" %}

{% block title %}{{ section.title }}{% endblock %}

{% block content %}
<h1>{{ section.title }}</h1>

{% for story in story_list %}
<h2>
  <a href="{{ story.get_absolute_url }}">
    {{ story.headline|upper }}
  </a>
</h2>
<p>{{ story.tease|truncatewords:"100" }}</p>
{% endfor %}
{% endblock %}

template variables

• Variables look like this: {{ variable }}.
• When the template engine encounters a variable, it evaluates that variable and replaces it with the result.
• Use a dot (.) to access attributes of a variable.

template.html

{{ section.title }}
{{ foo }}

template filters

• we can modify variables for display by using filters .
• filters look like this: {{ name|lower }} where name is a variable and lower is a filter.
• lower converts the value of name to lowercase

Filter	Description	Example Usage
date	Formats a date according to a given format string.	{{ my_date|date:"F j, Y" }}
time	Formats a time according to a given format string.	{{ my_time|time:"H" }}
default	Provides a default value if the variable is None or empty.	{{ my_var|default:"N/A" }}
default_if_none	Provides a default value only if the variable is None.	{{ my_var|default_if_none:"N/A" }}
length	Returns the length of the value.	{{ my_list|length }}
lower	Converts a string to lowercase.	{{ my_string|lower }}
upper	Converts a string to uppercase.	{{ my_string|upper }}
title	Converts a string to title case.	{{ my_string|title }}
truncatewords	Truncates a string to the specified number of words.	{{ my_string|truncatewords:3 }}
truncatechars	Truncates a string to the specified number of characters.	{{ my_string|truncatechars:10 }}
default	Returns a default value if the variable is None.	{{ name|default:"Guest" }}
length	Returns the length of the value.	{{ items|length }}
join	Joins a list with a string.	{{ list|join:", " }}
yesno	Converts boolean values to strings.	{{ my_bool|yesno:"yes,no,maybe" }}
safe	Marks a string as safe for HTML output.	{{ my_html|safe }}
escape	Escapes a string’s HTML.	{{ my_string|escape }}
linebreaks	Converts newlines into <p> and <br> tags.	{{ my_text|linebreaks }}
urlize	Converts URLs in plain text into clickable links.	{{ my_text|urlize }}
pluralize	Adds an 's' to a word if the value is not 1.	{{ count|pluralize }}
slice	Returns a slice of the value.	{{ my_list|slice:":2" }}
add	Adds a number to the value.	{{ num|add:5 }}
divisibleby	Returns True if the value is divisible by the argument.	{{ num|divisibleby:3 }}
filesizeformat	Formats a number of bytes as a human-readable file size.	{{ size|filesizeformat }}
first	Returns the first item in a list.	{{ my_list|first }}
last	Returns the last item in a list.	{{ my_list|last }}
random	Returns a random item from a list.	{{ my_list|random }}
striptags	Strips HTML tags from a string.	{{ my_html|striptags }}

template tags

• Tags look like this: {% tag %}.
• Some tags require beginning and ending tags (i.e.{% tag %} ... tag contents ... {% endtag %}).

Tag	Description	Example Usage
{% for %}	Loop over a sequence.	<ul> {% for item in items %} <li>{{ item }}</li> {% endfor %} </ul>
{% if %}	Conditional statement.	{% if user.is_authenticated %} <p>Welcome, {{ user.username }}!</p> {% else %} <p>Please log in.</p> {% endif %}
{% elif %}	Conditional elif clause.	{% if value < 10 %} <p>Less than 10</p> {% elif value < 20 %} <p>Less than 20</p> {% else %} <p>20 or more</p> {% endif %}
{% else %}	Conditional else clause.	{% if user.is_authenticated %} <p>Welcome, {{ user.username }}!</p> {% else %} <p>Please log in.</p> {% endif %}
{% block %}	Define a block that can be overridden in child templates.	{% block content %} <p>Content goes here.</p> {% endblock %}
{% extends %}	Inherit from another template.	{% extends "base.html" %}
{% include %}	Include another template within the current one.	{% include "navbar.html" %}
{% load %}	Load a custom template tag library.	{% load custom_tags %}
{% comment %}	Comment out a block of text.	{% comment %} This is a comment and will not be rendered. {% endcomment %}
{% csrf_token %}	Generate a CSRF token.	<form method="post"> {% csrf_token %} <!-- form fields --> </form>
{% static %}	Generate a URL for static files.	<img src="{% static 'images/logo.png' %}" alt="Logo">
{% url %}	Generate a URL for a view.	<a href="{% url 'app_name:view_name' %}">Link</a>
{% now %}	Display the current date and time.	<p>Today's date is {% now "Y-m-d" %}</p>
{% with %}	Create a new context variable.	{% with total=business.employees.count %} <p>Total employees: {{ total }}</p> {% endwith %}
{% autoescape %}	Control auto-escaping behavior.	{% autoescape off %} {{ data|safe }} {% endautoescape %}
{% spaceless %}	Remove whitespace between HTML tags.	{% spaceless %} <div> <span>Content</span> </div> {% endspaceless %}
{% cycle %}	Cycle among values for each iteration of a loop.	<ul> {% for o in some_list %} <li class="{% cycle 'odd' 'even' %}">{{ o }}</li> {% endfor %} </ul>
{% firstof %}	Output the first variable that is not empty.	{% firstof var1 var2 var3 %}
{% regroup %}	Group a list of objects by an attribute.	{% regroup items by category as grouped_items %} <ul> {% for group in grouped_items %} <li>{{ group.grouper }} <ul> {% for item in group.list %} <li>{{ item.name }}</li> {% endfor %} </ul> </li> {% endfor %} </ul>
{% verbatim %}	Disable template tag parsing for a block of text.	{% verbatim %} {{ raw_variable }} {% endverbatim %}

template inheritance

• The most powerful and complex – part of Django’s template engine is template inheritance.
• Template inheritance allows you to build a base “skeleton” template that contains all the common elements of your site and defines blocks that child templates can override.

base.html

<!DOCTYPE html>
<html lang="en">
<head>
    <link rel="stylesheet" href="style.css">
    <title>{% block title %}My amazing site{% endblock %}</title>
</head>

<body>
    <div id="sidebar">
        {% block sidebar %}
        <ul>
            <li><a href="/">Home</a></li>
            <li><a href="/blog/">Blog</a></li>
        </ul>
        {% endblock %}
    </div>

    <div id="content">
        {% block content %}{% endblock %}
    </div>
</body>
</html>

blog.html

{% extends "base.html" %}

{% block title %}My amazing blog{% endblock %}

{% block content %}
{% for entry in blog_entries %}
    <h2>{{ entry.title }}</h2>
    <p>{{ entry.body }}</p>
{% endfor %}
{% endblock %}

blog_page.html

{% extends "base.html" %}

{% block title %}Django is awesome {% endblock %}

{% block content %}
<div>
    Django’s template language is designed to strike a balance between power and ease. It’s designed to feel comfortable to those used to working with HTML. If you have any exposure to other text-based template languages, such as Smarty or Jinja2, you should feel right at home with Django’s templates.
</div>
{% endblock %}

Custom template filters

• Create a templatetags directory

  • Django will look for custom filter or tags in directory app/templatetags
  • Create custom filters module custom_filters.py

my_app/
    templatetags/
        __init__.py
        custom_filters.py

• Add custom filters to the module app/templatetags/custom_filters.py like below

from django import template

register = template.Library()

@register.filter(name='multiply')
def multiply(value, arg):
    """Multiplies the value by the arg."""
    return value * arg

• Load and use custom filters in template

{% load custom_filters %}
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Custom Filters</title>
</head>
<body>
    <h1>Custom Template Filters Example</h1>
    <p>Multiply 5 by 3: {{ 5|multiply:3 }}</p>
</body>
</html>

Custom template tags

• Create a templatetags directory

  • Django will look for custom filter or tags in directory app/templatetags
  • Create custom filters module custom_tags.py

my_app/
    templatetags/
        __init__.py
        custom_tags.py

• Add custom filters to the module app/templatetags/custom_tags.py like below

from django import template

register = template.Library()

@register.simple_tag
def current_time(format_string):
    """Returns the current time formatted according to the format_string."""
    from datetime import datetime
    return datetime.now().strftime(format_string)

• Load and use custom filters in template

{% load custom_tags %}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Custom Tags</title>
</head>
<body>
    <h1>Custom Template Tags Example</h1>
    <p>Current time: {% current_time "%Y-%m-%d %H:%M:%S" %}</p>
</body>
</html>

References

• https://docs.djangoproject.com/en/dev/ref/templates/language/
• https://docs.djangoproject.com/en/dev/ref/templates/builtins/
• https://docs.djangoproject.com/en/dev/ref/templates/api/