Overview
The Django Template Language (DTL) is a powerful tool for rendering dynamic web pages in Django. It allows developers to present data in HTML format by embedding Python-like expressions within the HTML. Understanding DTL and its extensibility is crucial for creating flexible and dynamic web applications with Django.
Key Concepts
- Syntax and Tags: The basic building blocks of DTL, including variables, tags, and filters.
- Inheritance: The mechanism by which templates can extend other templates, promoting code reuse.
- Custom Tags and Filters: How developers can extend the template language by creating their own tags and filters.
Common Interview Questions
Basic Level
- What is the syntax for inserting a variable into a Django template?
- How do you comment out code in a Django template?
Intermediate Level
- How can you extend a base template in Django?
Advanced Level
- Describe how you would create and use a custom template filter in Django.
Detailed Answers
1. What is the syntax for inserting a variable into a Django template?
Answer: To insert a variable into a Django template, you use double curly braces with the variable's name inside. The Django Template Engine will replace this with the variable's value when rendering the template.
Key Points:
- Variables can be passed from a view to the template and are accessed using {{ variable_name }}.
- You can also access attributes of a variable or index elements if the variable is an object or a list.
Example:
// Assuming this variable is passed to the template:
string name = "John";
// In the Django template, you would use:
{{ name }}
// This renders as:
John
2. How do you comment out code in a Django template?
Answer: In a Django template, you can comment out code or text using {# #}. Anything between these tags will not be rendered in the final HTML.
Key Points:
- Useful for adding notes or temporarily disabling parts of the template.
- Nested comments are not supported.
Example:
{# This is a comment and will not be rendered #}
<div>
{# Another comment: <p>Example paragraph</p> #}
</div>
3. How can you extend a base template in Django?
Answer: You can extend a base template in Django using the {% extends %} tag at the beginning of a child template. This allows the child template to inherit and override specific blocks from the base template.
Key Points:
- Extending templates promotes DRY (Don't Repeat Yourself) principles.
- Blocks in the base template can be overridden by blocks with the same name in the child template.
Example:
// Base template: base.html
<!DOCTYPE html>
<html>
<head>
{% block head %}{% endblock %}
</head>
<body>
{% block content %}{% endblock %}
</body>
</html>
// Child template
{% extends "base.html" %}
{% block head %}
<title>Child Page</title>
{% endblock %}
{% block content %}
<p>This is the content of the child page.</p>
{% endblock %}
4. Describe how you would create and use a custom template filter in Django.
Answer: Creating a custom template filter involves defining a Python function and registering it using the @register.filter decorator in a custom templatetags module. The custom filter can then be used in templates.
Key Points:
- Custom filters are useful for adding custom formatting or transforming template variables.
- Ensure your app contains a templatetags directory with an __init__.py file for custom filters to be recognized.
Example:
// In your_app/templatetags/custom_filters.py
from django import template
register = template.Library()
@register.filter(name='cut')
def cut(value, arg):
"""Removes all values of arg from the given string."""
return value.replace(arg, '')
// Usage in a template:
{{ somevariable|cut:" " }}
// If somevariable was "Hello World", the output would be "HelloWorld"
