What is Jinja?
Introduction
Jinja is a powerful and popular templating engine for Python. It is widely used in web frameworks like Flask and Django to generate dynamic HTML pages. Jinja allows developers to use control structures, filters, and macros to manipulate template data efficiently.
Features of Jinja
- Template Inheritance: Allows reuse of templates by extending base templates.
- Control Structures: Includes loops (
for), conditionals (if/else), and more. - Filters: Built-in functions to modify variables inside templates.
- Macros: Functions that allow reusable template code.
- Escaping: Prevents XSS attacks by escaping dangerous characters.
- Integration: Works seamlessly with Python frameworks like Flask and Django.
Installation of Jinja
Jinja is included with Flask but can also be installed separately using pip:
pip install Jinja2
To verify the installation, check the version:
python -c "import jinja2; print(jinja2.__version__)"
Basic Syntax of Jinja
Jinja templates use curly braces ({{ }}) for expressions and {% %} for statements.
Example Template
<!DOCTYPE html>
<html>
<head>
<title>{{ title }}</title>
</head>
<body>
<h1>Welcome, {{ user }}</h1>
{% if user == "Admin" %}
<p>You have admin privileges.</p>
{% else %}
<p>Standard user access.</p>
{% endif %}
</body>
</html>
Rendering the Template in Python
from jinja2 import Template
template = Template("Hello, {{ name }}!")
message = template.render(name="Harshvardhan")
print(message)
Output:
Hello, Harshvardhan!
Control Structures in Jinja
If-Else Condition
{% if age >= 18 %}
<p>You are eligible to vote.</p>
{% else %}
<p>You are not eligible to vote.</p>
{% endif %}
Loops (For Loop)
<ul>
{% for item in items %}
<li>{{ item }}</li>
{% endfor %}
</ul>
Using Filters
Filters modify variables in templates.
<p>{{ name | upper }}</p> <!-- Converts text to uppercase -->
<p>{{ price | round(2) }}</p> <!-- Rounds a number to 2 decimal places -->
Template Inheritance
Jinja supports template inheritance using {% extends %} and {% block %}.
Base Template (base.html)
<!DOCTYPE html>
<html>
<head>
<title>{% block title %}Default Title{% endblock %}</title>
</head>
<body>
<header>{% block header %}Default Header{% endblock %}</header>
<main>{% block content %}Default Content{% endblock %}</main>
</body>
</html>
Child Template (child.html)
{% extends "base.html" %}
{% block title %}Home Page{% endblock %}
{% block header %}Welcome to My Website{% endblock %}
{% block content %}<p>This is the home page content.</p>{% endblock %}
Using Jinja with Flask
Jinja is the default templating engine in Flask. To render an HTML template:
from flask import Flask, render_template
app = Flask(__name__)
@app.route('/')
def home():
return render_template('index.html', title='Home Page', user='Harshvardhan')
if __name__ == '__main__':
app.run(debug=True)
Conclusion
Jinja is a versatile and efficient templating engine that simplifies dynamic content rendering in Python applications. Its integration with web frameworks like Flask makes it an essential tool for developers. Mastering Jinja can significantly enhance the efficiency of your web development projects.
For more details, check the official Jinja documentation: https://jinja.palletsprojects.com.
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