Context Variable: Dot Lookup

$ python manage.py shell

• 1 dict

>>> from django.template import Template, Context
>>> 
>>> person = {'name': 'Sally', 'age': '43'}
>>> t = Template('{{ person.name }} is {{ person.age }} years old.')
>>> c = Context({'person': person})
>>> t.render(c)
'Sally is 43 years old.'

• 2 attribute

>>> from django.template import Template, Context
>>>
>>> class Person(object):
...     def __init__(self, first_name, last_name):
...         self.first_name, self.last_name = first_name, last_name
>>> t = Template('Hello, {{ person.first_name }} {{ person.last_name }}.')
>>> c = Context({'person': Person('John', 'Smith')})
>>> t.render(c)
'Hello, John Smith.'

• 3 Method

It’s not possible to pass arguments to the methods. You can only call methods that have no required arguments.

>>> from django.template import Template, Context
>>> t = Template('{{ var }} -- {{ var.upper }} -- {{ var.isdigit }}')
>>> t.render(Context({'var': 'hello'}))
'hello -- HELLO -- False'
>>> t.render(Context({'var': '123'}))
'123 -- 123 -- True'

• 4 list

Negative list indices are not allowed. For example, the template variable {{ items.-1 }} would cause aTemplateSyntaxError`.

>>> from django.template import Template, Context
>>>
>>> t = Template('Item 2 is {{ items.2 }}.')
>>> c = Context({'items': ['apples', 'bananas', 'carrots']})
>>> t.render(c)
'Item 2 is carrots.'

• 5 Invalid Variables

Generally, if a variable doesn’t exist, the template system inserts the value of the engine’s string_if_invalid configuration option, which is an empty string by default.

>>> from django.template import Template, Context
>>>
>>> t = Template('Your name is {{ name }}.')
>>> t.render(Context())
'Your name is .'
>>> t.render(Context({'var': 'hello'}))
'Your name is .'

• Dot lookup
  Dot lookups can be summarized like this: when the template system encounters a dot in a variable name, it tries the following lookups, in this order:
  • Dictionary lookup (e.g., foo["bar"])
  • Attribute lookup (e.g., foo.bar)
  • Method call (e.g., foo.bar())
  • List-index lookup (e.g., foo[2])

Tags

• 1 if-else

{% if ... %}
    ...
{% elif ... %}
    ...
{% else %}
   ...
{% endif %}

Use of actual parentheses in the if tag is invalid syntax.

• 2 for

{% for x in y_list %}
    ...
{% empty %}
  ...
{% endfor %}

the for tag supports an optional {% empty %} clause that lets you define what to output if the list is empty.

• 3 forloop

  • forloop.counter is always set to an integer representing the number of times the loop has been entered. This is one-indexed, so the first time through the loop, forloop.counter will be set to 1.

  • forloop.counter0 is like forloop.counter, except it’s zero-indexed. Its value will be set to 0 the first time through the loop.

  • forloop.revcounter is always set to an integer representing the number of remaining items in the loop. The first time through the loop, forloop.revcounter will be set to the total number of items in the sequence you’re traversing. The last time through the loop, forloop.revcounter will be set to 1.

  • forloop.revcounter0 is like forloop.revcounter, except it’s zero-indexed. The first time through the loop, forloop.revcounter0 will be set to the number of elements in the sequence minus 1. The last time through the loop, it will be set to 0.

  • forloop.first is a Boolean value set to True if this is the first time through the loop.

  • forloop.last is a Boolean value set to True if this is the last time through the loop.

  • forloop.parentloop is a reference to the forloop object for the parent loop, in case of nested loops.

• 4 comments

{# ...  #}      // one-line

{% comment %}    //multi-line
...
...
{% endcomment %}

filters

A filter argument comes after a colon and is always in double quotes.

{{ name|lower }}

Templates in views

• 1 settings.py
  set DIRS to [os.path.join(BASE_DIR,'templates')]

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [os.path.join(BASE_DIR,'templates')],
        'APP_DIRS': True,
        'OPTIONS': {
            # ...

• 2 create a \templates directory inside your root \mypro folder.

\mypro
   \mypro
   \templates
   manage.py

• 3 views.py

from django.template.loader import get_template
from django.http import HttpResponse
import datetime

def current_datetime(request):
    now = datetime.datetime.now()
    t = get_template('current_datetime.html')
    html = t.render({'current_date': now})
    return HttpResponse(html)

or

from django.shortcuts import render
import datetime

def current_datetime(request):
    now = datetime.datetime.now()
    return render(request, 'current_datetime.html', {'current_date': now})

• 4 current_datetime.html

<html>
    <body>
        It is now {{ current_date }}
    </body>
</html>

• 5 runserver

current time

• 6 Template Inheritance

base.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html lang="en">
<head>
    <title>{% block title %}{% endblock %}</title>
</head>
<body>
    <h1>My helpful timestamp site</h1>
    {% block content %}{% endblock %}

    {% block footer %}
    <hr>
    <p>Thanks for visiting my site.</p>
    {% endblock %}
</body>
</html>

current_datetime.html

{% extends "base.html" %}
{% block title %}The current time{% endblock %}
{% block content %}
    <p>It is now {{ current_date }}.</p>
{% endblock %}

hours_ahead.html

{% extends "base.html" %}
{% block title %}Future time{% endblock %}
{% block content %}
<p>
    In {{ hour_offset }} hour(s), it will be {{ next_time }}.
</p>
{% endblock %}

current time

hours_ahead

read more

• The django Book: Django Template

• The django Book: Django Template Tags and Filters

• The django Book: Built-in Template Tags and Filters

• Django documentation: Built-in Template Tags and Filters

• The django Book: Templates in Views