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Comprehensive Guide to Web Development with Python: From Flask to Django

Comprehensive Guide to Web Development with Python: From Flask to Django
Mohammad Waqas Shahid
Technical writer
Python
13.02.2024
Reading time: 14 min

Immense popularity has been gained by Python in web development because of its versatility and simplicity. This comprehensive guide will walk through the basics, covering Flask and Django frameworks, working with templates and views, database integration, handling forms, adding user authentication, and developing RESTful APIs. Following manual addresses towards steps on how to use Python for web development.

Flask and Django

Python has two frameworks for web development: Flask and Django. Both of these can be deployed on our app platform. Flask is a simple framework and is capable of making simple web apps as compared to Django which is more complex than Flask and also has more built-in features. Despite the differences, both frameworks are used by some of the most visited websites today. These sites include Netflix, Spotify, Uber, Zomato etc.

Getting started with Flask

Follow these steps to set up a basic Flask application:

  1. Install Flask using the following command:
pip install flask
  1. Create a new Python file, e.g., app.py, and add the following code:
from flask import Flask
app = Flask(__name__) 
@app.route('/')
def hello_world():
return 'Hello, Flask!'
  1. Run the application with:
flask run app.py

Afterwards, the terminal will output a link similar to http://127.0.0.1:5000/. By clicking this page, the app will appear in the user’s default browser with the instructions of “hello world” as was stated in the code.

Transitioning to Django

Django is a more robust framework that follows the Model-View-Controller (MVC) pattern. Install Django and create a project:

  1. Install Django using:
pip install django
  1. Create a new Django project:
django-admin startproject myproject
  1. Run the development server:  
python manage.py runserver

Afterwards, the terminal will output a link similar to http://127.0.0.1:8000/. By clicking this page, the app will appear in the user’s default browser.

Working with templates and views

In both Flask and Django, templates and views play a crucial role in rendering dynamic content. 

Create an HTML template in Flask

  1. Create a templates folder in Flask project folder.
  2. Add an HTML file, e.g., index.html, with your template.

Code for HTML is as follows: 

<!-- templates/index.html --> 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>{{ page_title }}</title>
</head>
<body>
    <header>
        <h1>{{ heading }}</h1>
    </header>
    <section>
        <p>{{ content }}</p>
    </section>
    <footer>
      <p>Your Flask App</p>
    </footer>
</body>
</html>

This HTML template includes placeholders (enclosed in double curly braces {{...}}) that Flask will replace with actual values during rendering.

Use templates in Flask

In the Flask application, the render_template function is used to render the HTML template with dynamic content. Below is an example:

# Example: Using templates in Flask
from flask import Flask, render_template app = Flask(__name__) @app.route('/') def home(): # Provide dynamic content to the template template_data = { 'page_title': 'Home Page', 'heading': 'Welcome to Flask!', 'content': 'This is a sample Flask web application.', } return render_template('index.html', **template_data) if __name__ == '__main__': app.run(debug=True)

In this example, the render_template function is used to render the index.html template with dynamic content provided by the template_data dictionary.

By incorporating this Flask-specific code, the HTML template is seamlessly integrated into the Flask application, allowing for the dynamic rendering of content.

Create an HTML template in Django

In order to create a view in Django, follow the stated guidelines:

  1. Define a view function in the views.py file.
from django.shortcuts import render
 
def index(request):
    context = {
        'page_title': 'Django Home',
        'heading': 'Welcome to Django!',
        'content': 'This is your Django app homepage.',
    }
    return render(request, 'your_app/index.html', context)

In this example, the index view function prepares a context dictionary with values for the placeholders in the HTML template. It then renders the index.html template using the render function.

  1. Map the view to a URL in urls.py.

Now, open the urls.py file in your app folder. Create a URL pattern that maps to the index view function.

from django.urls import path
from .views import index
 
urlpatterns = [
    path('', index, name='index'),
]

Database integration

Database integration is essential for dynamic web applications.

Connecting databases in Flask

  1. Add the following to your Flask app:
from flask_sqlalchemy import SQLAlchemy
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'
db = SQLAlchemy(app)
  1. Define models for your database.

Once Flask-SQLAlchemy is integrated, proceed to define models for your database. Databases are tables which are represented by models. In the Python programming language, these are Python classes. Below is a simplified example:

from datetime import datetime
from flask_sqlalchemy import SQLAlchemy
 
db = SQLAlchemy()
 
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(20), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    date_joined = db.Column(db.DateTime, default=datetime.utcnow)
 
    def __repr__(self):
        return f"User('{self.username}', '{self.email}')"

Connecting databases in Django

In Django, configuring databases is handled through the settings.py file. Follow these steps to set up a PostgreSQL database or another supported database:

  1. Modify settings.py.

Open the settings.py file within your Django project folder. Locate the DATABASES configuration section, and modify the ENGINE, NAME, USER, and PASSWORD parameters accordingly.

# Example: Configuring a PostgreSQL database in Django
 
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'your_database_name',
        'USER': 'your_database_user',
        'PASSWORD': 'your_database_password',
        'HOST': 'localhost',
        'PORT': '5432',
    }
}

Replace the placeholder values with your specific database details.

  1. Run migrations:

After modifying the database configuration, run the following commands to apply the changes and create necessary tables:

python manage.py makemigrations
python manage.py migrate

These commands create database tables based on the defined models.

With these configurations, your Flask application is now connected to a SQLite database, and your Django application is set up with the specified database, allowing seamless integration for dynamic web functionalities.

Handling forms and user input

Forms play a pivotal role in facilitating user interaction on web applications. This section delineates the process of creating a simple form in Flask using the WTForms library and constructing a form in Django through Django forms, integrated seamlessly with a view.

Form handling in Flask

Forms are vital for user interaction. Create a simple form in Flask:

  1. Use the WTForms library:
pip install Flask-WTF 
  1. Define a form in your Flask app.

Below is a basic example illustrating how to create a registration form using Flask-WTF:

# Example: Defining a simple form in Flask using WTForms 
from flask import Flask, render_template from flask_wtf import FlaskForm from wtforms import StringField, PasswordField, SubmitField app = Flask(__name__) app.config['SECRET_KEY'] = 'your_secret_key' class RegistrationForm(FlaskForm): username = StringField('Username') password = PasswordField('Password') submit = SubmitField('Register') @app.route('/register', methods=['GET', 'POST']) def register(): form = RegistrationForm() if form.validate_on_submit(): # Process the form data (e.g., save to database) return 'Registration successful!' return render_template('register.html', form=form)

In this example, the RegistrationForm class is created, defining fields for username, password, and a submit button. The form is then integrated into a route (/register), and upon submission, the data can be processed as needed.

Handling a form in Django

In Django, form handling is seamlessly integrated using Django forms. Follow these steps to create and integrate a form within your Django app.

  1. Define a form using Django's form framework. Below is an example of a simple registration form in Django:
from django import forms

class RegistrationForm(forms.Form):
    username = forms.CharField(label='Username', max_length=100)
    password = forms.CharField(label='Password', widget=forms.PasswordInput)
  1. Integrate the form with your view.

Integrate the form into your Django view. Modify your existing view or create a new one to handle the form submission:

from django.shortcuts import render
from .forms import RegistrationForm

def register(request):
    form = RegistrationForm(request.POST or None)

    if form.is_valid():
        # Process the form data (e.g., save to database)
        return render(request, 'registration_success.html')

    return render(request, 'register.html', {'form': form})

This example assumes the existence of HTML templates (register.html and registration_success.html) for rendering the form and success messages.

With these implementations, both Flask and Django applications can seamlessly handle forms, enabling effective user input and interaction.

Adding user authentication

User authentication is crucial for most web applications.

Secure user authentication in Flask

Implement authentication in Flask:

  1. Use Flask-Login for session management:
pip install flask-login
  1. Implement login and logout routes.

After installing Flask-Login, integrate it into your Flask application. Below is a simplified example illustrating the implementation of login and logout routes:

from flask import Flask, render_template,redirect,url_for
from flask_login import LoginManager, UserMixin, login_user, login_required, logout_user, current_user

app = Flask(__name__)
app.config['SECRET_KEY'] = 'your_secret_key'

# Sample User class (replace with your user model)
class User(UserMixin):
    def __init__(self, user_id):
        self.id = user_id

login_manager = LoginManager(app)
login_manager.login_view = 'login'

@login_manager.user_loader
def load_user(user_id):
    return User(user_id)

@app.route('/login')
def login():
    # Implement your login logic here
    user = User(user_id=1)
    login_user(user)
    return 'Login successful!'

@app.route('/logout')
@login_required
def logout():
    logout_user()
    return 'Logout successful!'

Customize the user authentication logic within the login route as per your application's requirements.

Secure user authentication in Django

In Django, use the built-in authentication system.

  1. Include django.contrib.auth in the INSTALLED_APPS list.

Open the settings.py file within your Django project folder. Locate the INSTALLED_APPS list and include django.contrib.auth:

INSTALLED_APPS = [
    # ... other apps ...
    'django.contrib.auth',
    # ... other apps ...
]
  1. Run migrations to create necessary tables.

Execute the following commands to apply migrations and create the necessary tables for user authentication:

python manage.py makemigrations
python manage.py migrate

These commands create tables such as auth_user needed for storing user authentication information.

With these implementations, both Flask and Django applications are equipped with secure user authentication mechanisms. Flask utilizes Flask-Login for session management, while Django leverages its built-in authentication system, ensuring the confidentiality and integrity of user credentials.

RESTful API development

RESTful APIs play a pivotal role in facilitating communication between different components of a web application

API development in Flask

  1. Define a Flask app and API endpoint.

In your Flask application, define a route that serves as your API endpoint. Below is an example:

# Example: Creating a simple API endpoint in Flask

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/api/hello', methods=['GET'])
def hello_world():
    return jsonify({'message': 'Hello, World!'})

This example creates a Flask app and a route (/api/hello) that returns a JSON response with a simple greeting.

  1. Run the Flask app.

Start your Flask development server to test the API endpoint:

flask run
  1. Visit http://127.0.0.1:5000/api/hello in your browser or a tool like Postman to interact with the API.

RESTful API in Django

  1. Ensure Django and Django REST Framework are installed. Use the following commands:
pip install django djangorestframework
  1. Create a Django Project and App, if not done already. Follow the standard Django project creation steps.
  1. In the Django app, define API views and serializers. Below is an example:
# In views.py
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status

class HelloWorld(APIView):
    def get(self, request):
        return Response({'message': 'Hello, World!'}, status=status.HTTP_200_OK)

# In serializers.py
from rest_framework import serializers

class HelloWorldSerializer(serializers.Serializer):
    message = serializers.CharField(max_length=100)
  1. Configure URLs in your app's urls.py file:
# In urls.py
from django.urls import path
from .views import HelloWorld

urlpatterns = [
    path('hello/', HelloWorld.as_view(), name='hello-world'),
]

This sets up a Django project with an API endpoint at http://127.0.0.1:8000/hello/.

  1. Run migrations and start Django development server. Write the following in your terminal:
python manage.py migrate
python manage.py runserver
  1. Visit http://127.0.0.1:8000/hello/ to interact with the Django API endpoint.

With these implementations, you've created a simple API endpoint in both Flask and Django, enabling seamless communication within your web applications.

Middleware and extensions

Enhancing Flask with Flask-Migrate and custom middleware

  1. Install Flask-Migrate.

Begin by installing Flask-Migrate, a Flask extension for handling database migrations:

pip install Flask-Migrate
  1. Initialize and perform database migrations.

Initialize the migration environment and apply migrations to your database:

flask db init
flask db migrate
flask db upgrade

These commands set up the necessary migration files and apply them to the database.

  1. Implement middleware in Flask.

In Flask, middleware allows you to define functions that run before and after request handling. As an example, let's create a simple logging middleware:

# Example: Simple logging middleware in Flask

from flask import Flask, request

app = Flask(__name__)

@app.before_request
def log_request_info():
    app.logger.info(f'Received request: {request.method} {request.url}')

@app.after_request
def log_response_info(response):
    app.logger.info(f'Sent response: {response.status_code}')
    return response

if __name__ == '__main__':
    app.run(debug=True)

This middleware logs information about incoming requests and outgoing responses.

Django with middleware

  1. Configure middleware in Django.

In Django, middleware classes are employed to process requests and responses globally. Add middleware classes in the MIDDLEWARE setting within your Django project's settings.py. As an illustration, let's add Django's built-in CommonMiddleware:

# Example: Configuring middleware in Django settings.py

MIDDLEWARE = [
    # ... other middleware classes
    'django.middleware.common.CommonMiddleware',
    # ... other middleware classes
]

CommonMiddleware adds security and performance-related headers to your responses.

  1. Create custom middleware in Django:

You can create custom middleware by defining a class with methods like process_request or process_response. Use the following example Python code:

# Example: Creating a custom logging middleware in Django

# In myapp/middleware.py
class LoggingMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        # Code to be executed for each response afte
        # the view is called.
        return response
  1. Add custom middleware to MIDDLEWARE:
# Example: Adding custom middleware to Django settings.py

MIDDLEWARE = [
    # ... other middleware classes
    'myapp.middleware.LoggingMiddleware',
    # ... other middleware classes
]

Ensure you replace myapp.middleware.LoggingMiddleware with the actual path to your middleware.

Conclusion

In conclusion, this comprehensive guide has equipped you with the fundamental knowledge of web development using Python. Whether you choose Flask for its simplicity or Django for its robust features, the skills learned here form a solid foundation for creating dynamic and powerful web applications. Now, go ahead and unleash the full potential of Python for web development.

Python
13.02.2024
Reading time: 14 min

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Understanding the main() Function in Python

In any complex program, it’s crucial to organize the code properly: define a starting point and separate its logical components. In Python, modules can be executed on their own or imported into other modules, so a well‑designed program must detect the execution context and adjust its behavior accordingly.  Separating run‑time code from import‑time code prevents premature execution, and having a single entry point makes it easier to configure launch parameters, pass command‑line arguments, and set up tests. When all important logic is gathered in one place, adding automated tests and rolling out new features becomes much more convenient.  For exactly these reasons it is common in Python to create a dedicated function that is called only when the script is run directly. Thanks to it, the code stays clean, modular, and controllable. That function, usually named main(), is the focus of this article. All examples were executed with Python 3.10.12 on a Hostman cloud server running Ubuntu 22.04. Each script was placed in a separate .py file (e.g., script.py) and started with: python script.py The scripts are written so they can be run just as easily in any online Python compiler for quick demonstrations. What Is the main() Function in Python The simplest Python code might look like: print("Hello, world!")  # direct execution Or a script might execute statements in sequence at file level: print("Hello, world!")       # action #1 print("How are you, world?") # action #2 print("Good‑bye, world...")  # action #3 That trivial arrangement works only for the simplest scripts. As a program grows, the logic quickly becomes tangled and demands re‑organization: # function containing the program’s main logic (entry point) def main():     print("Hello, world!") # launch the main logic if __name__ == "__main__":     main()                    # call the function with the main logic With more actions the code might look like: def main(): print("Hello, world!") print("How are you, world?") print("Good‑bye, world...") if __name__ == "__main__": main() This implementation has several important aspects, discussed below. The main() Function The core program logic lives inside a separate function. Although the name can be anything, developers usually choose main, mirroring C, C++, Java, and other languages.  Both helper code and the main logic are encapsulated: nothing sits “naked” at file scope. # greeting helper def greet(name): print(f"Hello, {name}!") # program logic def main(): name = input("Enter your name: ") greet(name) # launch the program if __name__ == "__main__": main() Thus main() acts as the entry point just as in many other languages. The if __name__ == "__main__" Check Before calling main() comes the somewhat odd construct if __name__ == "__main__":.  Its purpose is to split running from importing logic: If the script runs directly, the code inside the if block executes. If the script is imported, the block is skipped. Inside that block, you can put any code—not only the main() call: if __name__ == "__main__":     print("Any code can live here, not only main()") __name__ is one of Python’s built‑in “dunder” (double‑underscore) variables, often called magic or special. All dunder objects are defined and used internally by Python, but regular users can read them too. Depending on the context, __name__ holds: "__main__" when the module runs as a standalone script. The module’s own name when it is imported elsewhere. This lets a module discover its execution context. Advantages of Using  main() Organization Helper functions and classes, as well as the main function, are wrapped separately, making them easy to find and read. Global code is minimal—only initialization stays at file scope: def process_data(data): return [d * 2 for d in data] def main(): raw = [1, 2, 3, 4] result = process_data(raw) print("Result:", result) if __name__ == "__main__": main() A consistent style means no data manipulation happens at the file level. Even in a large script you can quickly locate the start of execution and any auxiliary sections. Isolation When code is written directly at the module level, every temporary variable, file handle, or connection lives in the global namespace, which can be painful for debugging and testing. Importing such a module pollutes the importer’s globals: # executes immediately on import values = [2, 4, 6] doubles = [] for v in values: doubles.append(v * 2) print("Doubled values:", doubles) With main() everything is local; when the function returns, its variables vanish: def double_list(items): return [x * 2 for x in items] # create a new list with doubled elements def main(): values = [2, 4, 6] result = double_list(values) print("Doubled values:", result) if __name__ == "__main__": main() That’s invaluable for unit testing, where you might run specific functions (including  main()) without triggering the whole program. Safety Without the __name__ check, top‑level code runs even on import—usually undesirable and potentially harmful. some.py: print("This code will execute even on import!") def useful_function(): return 42 main.py: import some print("The logic of the imported module executed itself...") Console: This code will execute even on import! The logic of the imported module executed itself... The safer some.py: def useful_function():     return 42 def main():     print("This code will not run on import") main() plus the __name__ check guard against accidental execution. Inside main() you can also verify user permissions or environment variables. How to Write main() in Python Remember: main() is not a language construct, just a regular function promoted to “entry point.” To ensure it runs only when the script starts directly: Tools – define helper functions with business logic. Logic – assemble them inside main() in the desired order. Check – add the if __name__ == "__main__" guard.  This template yields structured, import‑safe, test‑friendly code—excellent practice for any sizable Python project. Example Python Program Using main() # import the standard counter from collections import Counter # runs no matter how the program starts print("The text‑analysis program is active") # text‑analysis helper def analyze_text(text): words = text.split() # split text into words total = len(words) # total word count unique = len(set(words)) # unique word count avg_len = sum(len(w) for w in words) / total if total else 0 freq = Counter(words) # build frequency counter top3 = freq.most_common(3) # top three words return { 'total': total, 'unique': unique, 'avg_len': avg_len, 'top3': top3 } # program’s main logic def main(): print("Enter text (multiple lines). Press Enter on an empty line to finish:") lines = [] while True: line = input() if not line: break lines.append(line) text = ' '.join(lines) stats = analyze_text(text) print(f"\nTotal number of words: {stats['total']}") print(f"Unique words: {stats['unique']}") print(f"Average word length: {stats['avg_len']:.2f}") print("Top‑3 most frequent words:") for word, count in stats['top3']: print(f" {word!r}: {count} time(s)") # launch program if __name__ == "__main__": main() Running the script prints a prompt: Enter text (multiple lines). Press Enter on an empty line to finish: Input first line: Star cruiser Orion glided silently through the darkness of intergalactic space. Second line: Signals of unknown life‑forms flashed on the onboard sensors where the nebula glowed with a phosphorescent light. Third line: The cruiser checked the sensors, then the cruiser activated the defense system, and the cruiser returned to its course. Console output: The text‑analysis program is active Total number of words: 47 Unique words: 37 Average word length: 5.68 Top‑3 most frequent words: 'the': 7 time(s) 'cruiser': 4 time(s) 'of': 2 time(s) If you import this program (file program.py) elsewhere: import program         # importing program.py Only the code outside main() runs: The text‑analysis program is active So, a moderately complex text‑analysis utility achieves clear logic separation and context detection. When to Use main() and When Not To Use  main() (almost always appropriate) when: Medium/large scripts – significant code with non‑trivial logic, multiple functions/classes. Libraries or CLI utilities – you want parts of the module importable without side effects. Autotests – you need to test pure logic without extra boilerplate. You can skip main() when: Tiny one‑off scripts – trivial logic for a quick data tweak. Educational snippets – short examples illustrating a few syntax features. In short, if your Python program is a standalone utility or app with multiple processing stages, command‑line arguments, and external resources—introduce  main(). If it’s a small throw‑away script, omitting main() keeps things concise. Conclusion The  main() function in Python serves two critical purposes: Isolates the program’s core logic from the global namespace. Separates standalone‑execution logic from import logic. Thus, a Python file evolves from a straightforward script of sequential actions into a fully‑fledged program with an entry point, encapsulated logic, and the ability to detect its runtime environment.
14 July 2025 · 8 min to read

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