Boolean Operator - Django Template Tags

Boolean Operators

The “If” tags can be used with “and”, “or,” and “not” to test many variables depending on the context.

Let's look at a few examples considering we can have an employee and an employer list.

Case 1: Both employees and employers are present.

{% if emploee_list and employer_list %}

{% endif %}

Case 2:  If There are no employees present.

{% if not employee_list %}

{% endif %}

Case 3:  Some employees or a few employers are present.

{% if employee_list or employer_list %}

{% endif %}

Case 4:  There are no employees or few employers present.

{% if not employee_list or employer_list %}

{% endif %}

Case 5: A few employees and no employers are present.

{% if employee_list and not employer_list %}

{% endif %}

Case 6: Combination of case 4 and case 5.

We can use both “and” and “or” clauses in the same tag.


Note: The ”and” clause will appear first due to the precedence rule.

{% if employee_list and employer_list or customer_list %}

This condition will be written in the following way:

if (employee_list and employer_list) or customer_list

It is improper to use literal parentheses in the "if" tag. Use nested “if” tags if you require them to show precedence. The “if” tags may also use the operators, which will be explained one by one in the following examples.

== operator

This operator shows equality conditions. For example, if the variable equals the string "a".

{% if variable == "a" %}

{% endif %}

!= operator

This operator shows inequality conditions. For example, if the variable doesn't match the letter "a" or if it isn't even there in the text.

{% if variable != "a" %}

{% endif %}

< operator

This operator shows less than condition. For example, if the variable is less than 10.

{% if variable < 10 %}

{% endif %}

> operator

This operator shows greater than condition. For example, if the variable is greater than 10.

{% if variable > 10 %}

{% endif %}

<= operator

This operator shows less than or equal to the condition. For example, if the variable is less than 10 or equal to 10.

{% if variable <= 10 %}

{% endif %}

>= operator

This operator shows greater than or equal to the condition. For example, if the variable is greater than 10 or equal to 10.

{% if variable >= 10 %}

{% endif %}

in operator

This operator shows contained within the condition. The examples below show how “a” in “x” will be written.

Case 1: If "am" is a substring of "sample".

{% if "am" in "sample" %}

{% endif %}

Case 2: If “week” is a list or set, one element is the string "Monday".

{% if "Monday" in week%}

{% endif %}

Case 3: If “employees” is a Set, and if “employee” is an instance that belongs to the Set.

{% if employee in employees%}

{% endif %}

not in operator

This operator shows not contained within the condition. This is the “in” operator's negation.

is operator

This operator shows the object identity condition. It checks whether the two values represent the same object. 

Case 1: If and only if the variable is True.

{% if variable is True %}

{% endif %}

Case 2:  If the variable is none or is not found.

{% if variable is None %}

{% endif %}

is not operator

This operator shows the negated object identity condition. It checks whether the two values do not represent the same object. This is the “is” operator's negation.

Case 1: If the variable is not True or is not found.

{% if variable is not True %}

{% endif %}

Case 2: If and only if the variable is not “none”.

{% if variable is not None %}

{% endif %}

Implementation

Let's see how these templates can be used in a program.

Step 1:

First, install Django if you already haven't installed it in your system. For windows, follow the first command, macOS/Unix the second.

Windows: 

py -m pip install Django

MacOS/Unix:

python -m pip install Django

Step 2:

Create a project tempApp for the Django template by running the following command

django-admin startproject tempApp

Step 3:

Navigate to the tempApp folder and create an application temp for the Django template by running the following command

py manage.py startapp temp

Step 4:

In your application’s views.py file, define a view that returns a template. 

views.py

from django.shortcuts import render
def my_view(request):
	val1 = 4
	val2 = 13
	val3 = 20
	val4 = 22
	val5 = 50
	val6 = 60
	list = [4, 9, 13]
	return render(request, 'template.html', {
		'var1': val1,
		'var2': val2,
		'var3': val3,
		'var4': val4,
		'var5': val5,
		'var6': val6,
		'list': list
		})

Step 4:

Create an urls.py file in your application’s directory and add the following URL pattern. 

urls.py

from django.contrib import admin
from django.urls import path
from .views import my_view

urlpatterns = [
    path('', my_view ),
]

Step 5:

Add a URL pattern for the view in your project’s urls.py file, which can be found under the tempApp directory.

urls.py

from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path('', include('temp.urls')),
    path("admin/", admin.site.urls),
]

Step 6:

Create a folder named templates. In this folder, create a file called template.html. Add the following code to the template.html.

template.html

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Templates</title>
</head>
<body>
	{% if var1 == 4 %}
	<p>Value of var1 is equal to 4</p>
	{% endif %}

	{% if var2 != 11 %}
	<p>Value of var2 is not equal to 11</p>
	{% endif %}

	{% if var3 < 22 %} 
	<p>Value of var3 is less than 22</p>
	{% endif %}

	{% if var4 <= 28 %} 
	<p>Value of var4 is less than or equal to 28</p>
	{% endif %}

	{% if var5 > 40 %}
	<p>Value of var5 is greater than 40</p>
	{% endif %}

	{% if var6 >= 49 %}
	<p>Value of var6 is greater than or equal to 49</p>
	{% endif %}

	{% if 9 in list %}
	<p>9 is in the list</p>
	{% endif %}

	{% if not var7 %}
	<p>Value of var7 is False</p>
	{% endif %}

	{% if var1 == 4 and var5 > 11 %}
	<p>Value of var1 is equal to 4 and var5 is greater than 11</p>
	{% endif %}

	{% if var1 == 4 or var2 != 0 %}
	<p>Value of var1 is equal to 4 or var2 is not equal to 0</p>
	{% endif %}
</body>
</html>

Step 7: Add the application name under the INSTALLED_APPS in the settings.py file.

INSTALLED_APPS = [
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
    "temp"
] 

Note: After following the above steps, your file structure should look like this.

Output

Start the Django development server by running the following command on your terminal to attain an output.

python manage.py runserver

A link should be displayed on your terminal. Click on the link to see the template.

Here we can see how the templates work based on the above explanation.

Example:

var1 = 4 = val1

Therefore, in the template.html, when we give

......
{% if var1 == 4 %}
<p>Value of var1 is equal to 4</p>
{% endif %}
......

We get the output “Value of var1 is equal to 4”.

Frequently Asked Questions

What is a Django template?

It is a text file that is written using Django templating language. It gets rendered along with a set of variables defined in its context that can be used for updating the view the template will generate.

How does Django achieve scalability?

The Django web nodes do not have any stored state. This allows it to scale horizontally by firing up more web nodes when required.

What are templates in Django?

Templates are a way of creating dynamic Html pages with the help of python.

Are tags and filters the same?

No, they are not the same. With the help of filters, we can change the value, but we cannot do this using tags.

What are some other tags in Django templates?

Some other essential tags in Django are firstof, now, url, load, etc.

Conclusion

Congratulations on getting through this far! You saw how Django templates use template tags to manipulate the view. The examples clearly showed how we could use boolean operators in Django, like ==, !=, >=, < is, in, not inside template tags. To learn more about Django, you can go through the following blogs:

1. Getting started with Django
2. Django Template
3. Django Models
4. Reasons To Choose Django Framework
5. Tags in Django Templates
    

You may refer to our Guided Path on Code Studios for enhancing your skill set on DSA, Competitive Programming, System Design, etc. Check out essential interview questions, practice our available mock tests, look at the interview bundle for interview preparations, and so much more!

Happy Learning, Ninjas!