Логические операторы - теги шаблонов Django

Опубликовано: 24 Февраля, 2022

A Django template is a text document or a Python string marked-up using the Django template language. Django being a powerful Batteries included framework provides convenience to rendering data in a template. Django templates not only allow paassing data from view to template, but also provides some limited features of a programming such as variables, for loops, comments, extends, if else etc.
This article revolves about how to use boolean operators in Templates. The {% if %} tag evaluates a variable, and if that variable is “true” (i.e. exists, is not empty, and is not a false boolean value) the contents of the block are output. One can use various boolean operators with Django If Template tag.

Syntax

{% if variable boolean_operator value %}
// statements
{% endif %}

Example

if tags may use and, or or not to test a number of variables or to negate a given variable:

{% if athlete_list and coach_list %}
    Both athletes and coaches are available.
{% endif %}
  
{% if not athlete_list %}
    There are no athletes.
{% endif %}
  
{% if athlete_list or coach_list %}
    There are some athletes or some coaches.
{% endif %}
  
{% if not athlete_list or coach_list %}
    There are no athletes or there are some coaches.
{% endif %}
  
{% if athlete_list and not coach_list %}
    There are some athletes and absolutely no coaches.
{% endif %}

As one can see, the if tag may take one or several {% elif %} clauses, as well as an {% else %} clause that will be displayed if all previous conditions fail. These clauses are optional.

Boolean operators – Django template Tags Explanation

Illustration of How to use Boolean operators in Django templates using an Example. Consider a project named geeksforgeeks having an app named geeks.

Refer to the following articles to check how to create a project and an app in Django.
How to Create a Basic Project using MVT in Django?
How to Create an App in Django ?

Now create a view through which we will pass the context dictionary,
In geeks/views.py,

# import Http Response from django
from django.shortcuts import render
   
# create a function
def geeks_view(request):
    # create a dictionary
    context = {
        "data" : 99,
    }
    # return response
    return render(request, "geeks.html", context)

Create a url path to map to this view. In geeks/urls.py,

from django.urls import path
  
# importing views from views.py
from .views import geeks_view
  
urlpatterns = [
    path("", geeks_view),
]

Create a template in templates/geeks.html,

{% if data == 99 %}
Value in data is : - {{ data }}
{% else %}
Data is empty
{% endif%}

Let’s check what is displayed on “/” are displayed in the template.

Boolean Operators

== operator
Equality. Example:

{% if somevar == "x" %}
  This appears if variable somevar equals the string "x"
{% endif %}

!= operator
Inequality. Example:

{% if somevar != "x" %}
  This appears if variable somevar does not equal the string "x",
  or if somevar is not found in the context
{% endif %}

< operator
Less than. Example:

{% if somevar < 100 %}
  This appears if variable somevar is less than 100.
{% endif %}

> operator
Greater than. Example:

{% if somevar > 0 %}
  This appears if variable somevar is greater than 0.
{% endif %}

<= operator
Less than or equal to. Example:

{% if somevar <= 100 %}
  This appears if variable somevar is less than 100 or equal to 100.
{% endif %}

>= operator
Greater than or equal to. Example:

{% if somevar >= 1 %}
  This appears if variable somevar is greater than 1 or equal to 1.
{% endif %}

in operator
Contained within. This operator is supported by many Python containers to test whether the given value is in the container. The following are some examples of how x in y will be interpreted:

{% if "bc" in "abcdef" %}
  This appears since "bc" is a substring of "abcdef"
{% endif %}

{% if "hello" in greetings %}
  If greetings is a list or set, one element of which is the string
  "hello", this will appear.
{% endif %}

{% if user in users %}
  If users is a QuerySet, this will appear if user is an
  instance that belongs to the QuerySet.
{% endif %}

not in operator
Not contained within. This is the negation of the in operator.

is operator
Object identity. Tests if two values are the same object. Example:

{% if somevar is True %}
  This appears if and only if somevar is True.
{% endif %}

{% if somevar is None %}
  This appears if somevar is None, or if somevar is not found in the context.
{% endif %}

is not operator
Negated object identity. Tests if two values are not the same object. This is the negation of the is operator. Example:

{% if somevar is not True %}
  This appears if somevar is not True, or if somevar is not found in the
  context.
{% endif %}

{% if somevar is not None %}
  This appears if and only if somevar is not None.
{% endif %}

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Логические операторы - теги шаблонов Django

Syntax

Example

Boolean operators – Django template Tags Explanation

Boolean Operators

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