Jinja if/else statements in Python

Jinja is a popular templating language used in various web development frameworks such as Flask and Django. It provides a way to create dynamic HTML templates by embedding Python code within HTML files.

One of the most important features of Jinja is the ability to use if/else statements to control the flow of data in templates. This allows programmers to conditionally render certain parts of the template based on the values of variables.

Syntax of Jinja if/else statements:

{% if condition %}
    <!-- HTML code to be rendered if condition is true -->
{% else %}
    <!-- HTML code to be rendered if condition is false -->
{% endif %}

Here, condition is a Python expression that evaluates to either True or False. If the condition is true, the code block inside the "if" statement is executed, otherwise, the code block inside the "else" statement is executed.

Examples:

Let's look at a few examples to understand how to use Jinja if/else statements in Python:

Example 1:

Suppose you have a variable named score and you want to display a message based on the value of score. You can use the following code:

{% if score >= 80 %}
    <p>Excellent work!</p>
{% else %}
    <p>Keep improving!</p>
{% endif %}

In this example, if the score is greater than or equal to 80, the message "Excellent work!" will be rendered. Otherwise, the message "Keep improving!" will be rendered.

Example 2:

Imagine you have a list of names and you only want to display the names that start with the letter "J". You can use the following code:

<ul>
{% for name in names %}
    {% if name[0] == 'J' %}
        <li>{{ name }}</li>
    {% endif %}
{% endfor %}
</ul>

In this example, the template loops through the names list and checks if each name starts with the letter "J". If it does, the name is rendered as a list item. Only the names that satisfy the condition will be displayed.

Conclusion:

Jinja if/else statements provide a powerful way to conditionally render HTML content based on the values of variables. By using these statements, you can create dynamic templates that adapt to different situations. Jinja's flexible syntax and Python integration make it a popular choice among web developers.