Learn Django 3 and Start Creating Websites With Python

Django is the most popular web framework for building web applications with Python. It provides a powerful set of tools and conventions that allow developers to create complex, data-driven websites quickly and efficiently. In this comprehensive guide, we‘ll walk through everything you need to know to get started with Django 3 and begin creating your own fully-featured web apps.

What is Django?

Django is a free and open-source framework that follows the Model-View-Controller (MVC) architectural pattern. It‘s designed to simplify the creation of database-driven websites by providing reusable components, an object-relational mapper (ORM) for interacting with databases, and a template engine for rendering dynamic HTML pages.

Some of the key features and benefits of Django include:

• DRY (Don‘t Repeat Yourself) principle: Django promotes code reusability and avoids duplication.
• Batteries included: It comes with many built-in features for common web development tasks.
• Scalability: Django uses a component-based "shared-nothing" architecture that allows scaling of applications.
• Security: It provides built-in protection against common web vulnerabilities like cross-site scripting, SQL injection, etc.
• Admin interface: Django offers a production-ready automatic admin interface to manage your application‘s data.
• Excellent documentation and large community: Django has thorough documentation and a vast, supportive developer community.

Getting Started

Before diving into Django, you should have a solid grasp of core Python concepts like data types, control flow, functions, classes, etc. Familiarity with HTML and CSS is also beneficial for working with templates and styling your application.

To install Django, you‘ll first need Python and pip (Python package manager) set up on your system. It‘s recommended to use a virtual environment to isolate your Django project‘s dependencies from other Python projects on your machine. You can create a virtual environment and install the latest version of Django with the following commands:

python -m venv myenv 
source myenv/bin/activate
pip install django

Once Django is installed, you can start a new project using the django-admin command-line utility:

django-admin startproject myproject
cd myproject
python manage.py runserver

This will create a new project directory and start a development server at http://127.0.0.1:8000/. You should see a default Django landing page when you visit this URL in your web browser.

Key Django Concepts

Let‘s go over some of the core components and concepts you‘ll work with in a Django project:

Models

Models define the structure and data types of your application‘s database tables. They are defined as Python classes that inherit from django.db.models.Model. Each model attribute represents a database field. For example:

from django.db import models

class Customer(models.Model):
    name = models.CharField(max_length=120)
    logo = models.ImageField(upload_to=‘customers‘, default=‘no_picture.png‘)

    def __str__(self):
        return str(self.name)

This model represents a Customer table with name and logo fields. The __str__ method provides a human-readable string representation of each Customer instance.

Views

Views determine what data gets shown to the user and how. They retrieve data from models and pass it to templates for rendering. Views are Python functions or classes that take a web request and return a web response. For example:

from django.shortcuts import render
from .models import Customer

def customer_list_view(request):
    customers = Customer.objects.all()
    return render(request, ‘customers/main.html‘, {‘customers‘: customers})

This view retrieves all Customer objects from the database and renders them in a template located at customers/main.html, passing the customers data to the template context.

Templates

Templates define the structure and layout of your application‘s user interface, written in HTML with special syntax for rendering dynamic data. Django‘s template language allows embedding Python-like code for tasks like looping, conditionals, filters, etc. For example:

<ul>
{% for customer in customers %}
    <li>
        <img src="{{ customer.logo.url }}" />
        <p>{{ customer.name }}</p>  
    </li>
{% endfor %}
</ul>

This template loops through the customers data passed from the view and renders an image and name for each customer instance.

URLs

URLs map web requests to the appropriate view functions based on the requested URL pattern. URL configuration is defined in a `urls.py` file using path() and re_path() methods. For example:

from django.urls import path
from . import views

urlpatterns = [
    path(‘customers/‘, views.customer_list_view, name=‘customer-list‘),
]

This configuration maps the /customers/ URL pattern to the customer_list_view function defined earlier.

Building Features with Django

With the key concepts covered, let‘s explore some of the powerful features you can create in a Django web application.

User Authentication

Django comes with a built-in user authentication system that handles user accounts, groups, permissions, and cookie-based user sessions. You can easily add login, logout, and registration functionality to your application. Here‘s an example view for logging in a user:

from django.contrib.auth import authenticate, login
from django.shortcuts import render, redirect

def login_view(request):
    if request.method == ‘POST‘:
        username = request.POST[‘username‘]
        password = request.POST[‘password‘]
        user = authenticate(request, username=username, password=password)
        if user is not None:
            login(request, user)
            return redirect(‘home‘)
    return render(request, ‘login.html‘)

This view authenticates a user based on submitted username and password, logs them in if credentials are valid, and redirects to a home page.

Database Queries and Aggregation

Django‘s ORM provides an expressive query API for retrieving and filtering data from your models. You can chain methods to build complex queries and perform aggregations. For example:

from django.db.models import Sum, Avg

sales = Sale.objects.filter(customer__name=‘ABC Inc‘)
                    .aggregate(total_revenue=Sum(‘amount‘), 
                               average_revenue=Avg(‘amount‘))

This query retrieves all sales for the customer with name "ABC Inc", and calculates the total and average revenue using aggregate functions.

File Uploads and Downloads

Django makes it easy to accept file uploads from users and serve files for download. You can define model fields for file attachments, configure upload directories, and add upload handling to your views. For example:

from django.views.decorators.http import require_POST
from django.http import JsonResponse

@require_POST
def upload_sales_csv(request):
    csv_file = request.FILES.get(‘file‘)

    if csv_file:
        # Process uploaded CSV
        # ...
        return JsonResponse({‘message‘: ‘CSV processed successfully.‘})

    return JsonResponse({‘message‘: ‘No file was uploaded.‘}, status=400) 

This view accepts a POST request with a CSV file, performs some processing on it, and returns a JSON response indicating the upload status.

Integrating with Other Libraries

Django seamlessly integrates with a vast ecosystem of Python libraries and tools for additional functionality. Some popular libraries to use with Django include:

• pandas: For data manipulation and analysis
• matplotlib and Seaborn: For data visualization
• django-crispy-forms: For building elegant forms with validation and layout control
• django-rest-framework: For creating RESTful APIs
• django-allauth: For adding social authentication (OAuth) to your application

Here‘s an example of rendering a pandas DataFrame in a Django template after performing some analysis:

import pandas as pd
import matplotlib.pyplot as plt
from io import BytesIO
import base64

def sales_report_view(request):
    sales_df = pd.read_csv(‘sales_data.csv‘)
    sales_per_month = sales_df.groupby(pd.Grouper(key=‘date‘, freq=‘M‘))[‘amount‘].sum()

    # Generate a plot
    buffer = BytesIO()
    plt.plot(sales_per_month.index, sales_per_month.values)
    plt.savefig(buffer, format=‘png‘)
    buffer.seek(0)
    image_base64 = base64.b64encode(buffer.read()).decode()

    context = {‘sales_per_month‘: sales_per_month, ‘chart‘: image_base64}
    return render(request, ‘sales_report.html‘, context)

This view loads sales data from a CSV into a pandas DataFrame, performs a grouping and aggregation to get total sales per month, generates a matplotlib plot, and renders the DataFrame and chart in a template.

Deploying Django Applications

Once you‘ve built your Django application, you‘ll want to deploy it to a production environment so users can access it. Some popular deployment options include:

• PythonAnywhere: A beginner-friendly platform for deploying Python web applications
• Heroku: A cloud platform that supports Django deployments with managed infrastructure
• DigitalOcean: Cloud servers (droplets) that give you full control over your deployment
• AWS, Azure, GCP: Major cloud providers with various deployment services for Django

The Django documentation provides detailed guides for production deployments, including settings configuration, static file handling, database setup, and more.

Conclusion and Next Steps

In this guide, we‘ve covered the fundamentals of building web applications with Django 3, including key concepts, features, integrations, and deployment. To continue your Django learning journey, some suggested next steps are:

1. Build a complete project: Apply what you‘ve learned to create a full-stack web application from scratch.
2. Explore advanced topics: Dive deeper into areas like testing, caching, security, performance optimization, etc.
3. Contribute to open-source: Many Django packages and projects welcome contributions from the community.
4. Join the community: Participate in forums, attend meetups and conferences, and learn from experienced Django developers.

With its powerful features and active community, Django is an excellent choice for building robust, scalable web applications. It has been used to create many successful websites like Instagram, Mozilla, Bitbucket, and more. By mastering Django, you‘ll have a valuable skill set for back-end web development in the Python ecosystem.

Happy coding!