Django Templates, Context, Template Tags and filters

Django Templates, Context, Template Tags and filters

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Django The Right Way

Published on Jun 19, 2021

6 min read

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When working with web frameworks at some point rendering data directly through your controller or views is not efficient. Let's take an example of code snippet from our first article in this series Django Setup, Architecture and Hello World which looks like

from django.http import HttpResponse


def hi_view(request):
    response = """
    <html>
        <body>
            <h1>Hello world</h1>
        </body>
    </html>
    """
    return HttpResponse(response)

Here we trying to send whole bunch of HTML code from the views itself. This might look easy and so clean to see in this example but trust me as your project grows up and when you will have 100's and 1000's of HTML code this method will be pain and unmanageable.

So how do we write templates in a manageable way and make it dynamic as well? The answer is through the help of Template System provided by the framework.

Django Template

  • A template can have some static HTML parts and some dynamic content to be inserted in between the HTML
  • A very efficient and convenient way of generating HTML dynamically
  • Django has built-in backend for its own template system which is called Django Template Language (DTL) and also for the popular alternative Jinja2

For the sake of simplicity we will be using Django Template Language (DTL) which is preconfigured on settings.py when creating our project using django-admin command line utility i.e: django-admin startproject project_name

You may have already heard about Jinja if you are from the Flask background. Let me know through RFA form or comments if i should make some tutorial on Jinja

So where are template engine configured?

If you open up your settings.py file or if you followed me through Django Setup, Architecture and Hello World then you will find your settings.py file under meme/settings.py since we created meme django project you will see something like

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

You can see BACKEND key which points to dotted path for DjangoTemplates and other settings there like DIRS where the template engine will look for the html files

Let's get to know last checklist before we jump in

  • To pass any value (some dynamic contents like blog post, user info fetched from the DB e.t.c) from view (view function) to the template (html files) we pass it as context.
  • Context means a plain dictionary of key and value (K:V) i.e {'name':'John'}
  • You can always provide as much template directory on your settings.py under TEMPLATEs-->DIRS
  • Since APP_DIRS=True in our above settings, the template finder will search inside our INSTALLED_APPS-->templates/ folder as well.
  • So this means, you can add your templates under the directory provided in DIRS or under templates/ directory under your app folder

So, where should i actually put my HTML files? The simple answer is if your HTML file is is for local app use only then put it inside templates/ folder of your apps or else if the HTML file is used globally in all your apps then put it under the DIRS folder which is usually templates/ folder inside your project directory

Loading and rendering a template

First let's create a simple template under our DIRS directory or under templates/ inside our app.

To make it more clear, lets create a new app named smile through help of dango command python manage.py startapp smile and register this app to the settings.py file and as soon as you register your app create templates folder inside your app and create a HTML file smile.html

We created a new app, so do you remember as soon as we create a new app we need to add this to the INSTALLED_APPS on our settings.py file

Under your smile/templates/smile.html or if create any HTML file you like.

    <html>
        <body>
            <h1>Today's special joke</h1>
            <h1> {{ joke }}</h1>
        </body>
    </html>

But, whats the {{ joke }} thing inside this HTML file. This is a way to insert dynamic content to the HTML file. This dynamic content or values are sent from views in the form of context we talked earlier

If your template doesn't have any dynamic contents to be inserted then that's fine as well, many of your page can have a static HTML as well

So, lets use and render this templates create a view function

# views.py
from django.http import HttpResponse
from django.template import loader


def joke_view(request):
    # load the template that you just created 
    template = loader.get_template(template_name='smile.html') 

    # create context
    context = {
        'joke': 'This is really funny joke !!'
    }

    result = template.render(context, request)
    return HttpResponse(result)

Now, quickly create up a URL path for this view functions like we did on our previous tutorial and you should see something like this when you visit your URL

django-template-and-context-initial-preview.png

But wait, there are shortcuts for easy rendering of templates

The view function joke_view() we just created can also be written as

from django.shortcuts import render


def joke_view(request):
    # create context
    context = {
        'joke': 'This is really funny joke !!'
    }
    return render(request, 
                  template_name="smile.html", 
                  context=context)

More on Context rendering and working with Templates

Variables

  • Outputs/prints the value from the context
  • Variables are surrounded by {{ }} (just like we did it just above)
Examples

Lets assume HTML template to be Hi, i am from {{ location }} and i love {{ lang }}. So,

  • context={'location':'Earth','lang':'Python'} on this HTML template would render to Hi, i am from Earth and i love Python.
  • context={'location':'Mars','lang':'Javascript'} on this HTML template would render to Hi, i am from Mars and i love Javascript.

Tags

  • A tag can be used to output content
  • It can be used to perform control structure i.e: if/else, loops
  • It can do many things to make your template dynamic
  • Tags are surrounded by {% %}
  • Some tags require ending tags where as some doesn't need it
    • {% csrf_token %} has no ending tag
    • {% if user.is_authenticated %}Hello, {{ user.username }}.{% endif %}​ has ending tag
Examples
  • for loops over each item in an array
    {% for language in language_list %}
         <li>{{ language }}</li>
    {% endfor %}
    
    where language_list is a iterable sent from view function as a context
  • if

    {% if language_list %}
      Number of language: {{ language_list|length }}
    {% else %}
      <h1>No Languages found.</h1>
    {% endif %}
    

    it even supports elif don't forget to try it

  • now displays current date and/or time
     It is {% now "jS F Y H:i" %}
    

Filters

  • Filter transform the values of variables and tag arguments
Examples
  • add adds the arguments to the value
    {{ number|add:"10" }}
    
    would output 100 if the value of number is 90. The value of number is sent as context from the view function as context={'number':90}
  • capfirst capitalizes the first character of the value
      {{ name|capfirst }}
    
  • default provides a default value if existing value evaluates to False
      {{ country|default:"Not Selected" }}
    
    If country is empty "" (empty string) then output will be Not Selected

Comments

  • Comments are placed in {# #} which are not rendered on templates during rendering process
Examples
{# this is a comment and will not be rendered #}

Last Note

We looked into tags and filters and saw some examples. I tried to make it easy as possible and lastly want to let you know there are so many builtin tags and filters inside django. Please have a look into official django docs https://docs.djangoproject.com/en/3.2/ref/templates/builtins/ to see the complete list.

You can always create your own template tags and filter, trust me they make working with templates very easy