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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

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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. 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14 July 2025 · 8 min to read
Python

Python Static Method

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Here's an example from a User class that checks email format: class User: @staticmethod def is_valid_email(email): return "@" in email and "." in email This method doesn't depend on any part of the User instance, but conceptually belongs in the class. It can be used anywhere as User.is_valid_email(email), keeping your code cleaner and more organized. If the logic requires access to or modification of instance attributes or class-level data, avoid using a static method as it won't help here. For instance, if you are working with user settings or need to monitor object creation, you will require a class method or an instance method instead. class Counter: count = 0 @classmethod def increment(cls): cls.count += 1 In this example, using a static method would prevent access to cls.count, making it useless for this kind of task. Python Static Method vs Class Method Though they look similar, class and static methods in Python have different uses; so, let's now quickly review their differences. Defined inside a class, a class method is connected to that class rather than an instance. Conventionally called cls, the class itself is the first parameter; so, it can access and change class-level data. Factory patterns, alternate constructors, or any activity applicable to the class as a whole and not individual instances are often implemented via class methods. Conversely, a static method is defined within a class but does not start with either self or cls parameters. It is just a regular function that “lives” inside a class but doesn’t interact with the class or its instances. For utility tasks that are conceptually related to the class but don’t depend on its state, static methods are perfect. 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Managed solution for Backend development Example #2 Let's say we're working with a StringUtils module with a static method for checking if a string is a palindrome. The code will be: def is_palindrome(string):    return string == string[::-1] This function doesn't rely on any instance-specific data — it simply performs a check on the input. That makes it a good candidate for a static method. To organize it within a class and signal that it doesn't depend on the class state, we can use the @staticmethod decorator like this: class StringUtils:    @staticmethod    def is_palindrome(string):       return string == string[::-1] Let's enter for verification: print(StringUtils.is_palindrome("deed"))True print(StringUtils.is_palindrome("deer"))False That's correct, the first word is a palindrome, so the interpreter outputs True, but the second word is not, and we get False. So, we can call the is_palindrome method through the StringUtils class using the StringUtils.is_palindrome(string) syntax instead of importing the is_palindrome function and calling it directly. - Python static method and class instance also differ in that the static cannot affect the state of an instance. Since they do not have access to the instance, they cannot alter attribute values, which makes sense. Instance methods are how one may modify the instance state of a class. Example #3 Let's look at another example. Suppose we have a Person class that has an age attribute and a static is_adult method that checks the value against the age of majority: class Person:    def __init__(self, age):        self.age = age    @staticmethod    def is_adult(age):       return age >= 21 Next, let's create an age variable with a value of 24, call the is_adult static method from the Person class with this value and store its result in the is_adult variable, like this: age = 24is_adult = Person.is_adult(age) Now to test this, let's enter: print(is_adult)True Since the age matches the condition specified in the static method, we get True. In the example, the is_adult static method serves as an auxiliary tool—a helper function—accepting the age argument but without access to the age attribute of the Person class instance. Conclusion Static methods improve code readability and make it possible to reuse it. They are also more convenient when compared to standard Python functions. Static methods are convenient as, unlike functions, they do not call for a separate import. Therefore, applying Python class static methods can help you streamline and work with your code greatly. And, as you've probably seen from the examples above, they are quite easy to master. On our app platform you can find Python applications, such as Celery, Django, FastAPI and Flask. 
16 April 2025 · 6 min to read
Python

Input in Python

Python provides interactive capabilities through various tools, one of which is the input() function. Its primary purpose is to receive user input. This function makes Python programs meaningful because without user interaction, applications would have limited utility. How the Python Input Works This function operates as follows: user_name = input('Enter your name: ') user_age = int(input('How old are you? ')) First, the user is asked to enter their name, then their age. Both inputs are captured using a special operator that stores the entered values in the variables user_name and user_age. These values can then be used in the program. For example, we can create an age-based access condition for a website (by converting the age input to an integer using int()) and display a welcome message using the entered name: if user_age < 18: print('Sorry, access is restricted to adults only') else: print('Welcome to the site,', user_name, '!') So, what happens when int() receives an empty value? If the user presses Enter without entering anything, let's see what happens by extending the program: user_name = input('Enter your name: ') user_age = int(input('How old are you? ')) if user_age < 18: print('Sorry, access is restricted to adults only') else: print('Welcome to the site,', user_name, '!') input('Press Enter to go to the menu') print('Welcome to the menu') Pressing Enter moves the program to the next line of code. If there is no next line, the program exits. The last line can be written as: input('Press Enter to exit') If there are no more lines in the program, it will exit. Here is the complete version of the program: user_name = input('Enter your name: ') user_age = int(input('How old are you? ')) if user_age < 18: print('Sorry, access is restricted to adults only') else: print('Welcome to the site,', user_name, '!') input('Press Enter to go to the menu') print('Welcome to the menu') input('Press Enter to exit') input('Press Enter to exit') If the user enters an acceptable age, they will see the message inside the else block. Otherwise, they will see only the if block message and the final exit prompt. The input() function is used four times in this program, and in the last two cases, it does not store any values but serves to move to the next part of the code or exit the program. input() in the Python Interpreter The above example is a complete program, but you can also execute it line by line in the Python interpreter. However, in this case, you must enter data immediately to continue: >>> user_name = input('Enter your name: ') Enter your name: Jamie >>> user_age = int(input('How old are you? ')) How old are you? 18 The code will still execute, and values will be stored in variables. This method allows testing specific code blocks. However, keep in mind that values are retained only until you exit the interactive mode. It is recommended to save your code in a .py file. Input Conversion Methods: int(), float(), split() Sometimes, we need to convert user input into a specific data type, such as an integer, a floating-point number, or a list. Integer conversion (int()) We've already seen this in a previous example: user_age = int(input('How old are you? ')) The int() function converts input into an integer, allowing Python to process it as a numeric type. By default, numbers entered by users are treated as strings, so Python requires explicit conversion. A more detailed approach would be: user_age = input('How old are you? ') user_age = int(user_age) The first method is shorter and more convenient, but the second method is useful for understanding function behavior. Floating-point conversion (float()) To convert user input into a floating-point number, use float(): height = float(input('Enter your height (e.g., 1.72): ')) weight = float(input('Enter your weight (e.g., 80.3): ')) Or using a more detailed approach: height = input('Enter your height (e.g., 1.72): ') height = float(height) weight = input('Enter your weight (e.g., 80.3): ') weight = float(weight) Now, the program can perform calculations with floating-point numbers. Converting Input into a List (split()) The split() method converts input text into a list of words: animals = input('Enter your favorite animals separated by spaces: ').split() print('Here they are as a list:', animals) Example output: Enter your favorite animals separated by spaces: cat dog rabbit fox bear Here they are as a list: ['cat', 'dog', 'rabbit', 'fox', 'bear'] Handling Input Errors Users often make mistakes while entering data or may intentionally enter incorrect characters. In such cases, incorrect input can cause the program to crash: >>> height = float(input('Enter your height (e.g., 1.72): ')) Enter your height (e.g., 1.72): 1m72 Traceback (most recent call last): File "<pyshell#2>", line 1, in <module> height = float(input('Enter your height (e.g., 1.72): ')) ValueError: could not convert string to float: '1m72' The error message indicates that Python cannot convert the string into a float. To prevent such crashes, we use the try-except block: try: height = float(input('Enter your height (e.g., 1.72): ')) except ValueError: height = float(input('Please enter your height in the correct format: ')) We can also modify our initial age-input program to be more robust: try: user_age = int(input('How old are you? ')) except ValueError: user_age = int(input('Please enter a number: ')) However, the program will still crash if the user enters incorrect data again. To make it more resilient, we can use a while loop: while True: try: height = float(input('Enter your height (e.g., 1.72): ')) break except ValueError: print('Let’s try again.') continue print('Thank you!') Here, we use a while loop with break and continue. The program works as follows: If the input is correct, the loop breaks, and the program proceeds to the final message: print('Thank you!'). If the program cannot convert input to a float, it catches an exception (ValueError) and displays the message "Let’s try again."  The continue statement prevents the program from crashing and loops back to request input again. Now, the user must enter valid data before proceeding. Here is the complete code for a more resilient program: user_name = input('Enter your name: ') while True: try: user_age = int(input('How old are you? ')) break except ValueError: print('Are you sure?') continue if user_age < 18: print('Sorry, access is restricted to adults only') else: print('Welcome to the site,', user_name, '!') input('Press Enter to go to the menu') print('Welcome to the menu') input('Press Enter to exit') This program still allows unrealistic inputs (e.g., 3 meters tall or 300 years old). To enforce realistic values, additional range checks would be needed, but that is beyond the scope of this article. 
08 April 2025 · 6 min to read

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