2026-03-276 min read

Website (Python Programming)

Q: Q: How do I run my Flask application?

To run your Flask application, save your `app.py` file and any associated templates in the same directory, then execute the following command in your terminal or command prompt: `python app.py`.

Learn Website (Python Programming) step by step with clear examples and exercises.

Why This Matters

Creating a website is an essential skill for anyone looking to make their mark on the digital world. Whether you're building a personal blog, an e-commerce store, or a professional portfolio, Python offers a powerful and versatile toolset to get the job done. In this lesson, we will delve into creating a basic webpage using Python, exploring its practical depth, common mistakes, and best practices.

Why Web Development with Python Matters

Web development is an integral part of modern technology, and having proficiency in Python for web development can open up numerous opportunities. By understanding how to create websites with Python, you'll be able to build dynamic, interactive applications that cater to a wide range of user needs. Moreover, learning Python web development can serve as a stepping stone towards mastering more complex frameworks like Django and Pyramid.

Prerequisites

To follow along with this tutorial, you should have a basic understanding of Python syntax and data structures, including variables, functions, loops, and conditional statements. Familiarity with HTML and CSS is also helpful but not required as we will cover the basics within this lesson. Additionally, it's essential to have Python installed on your computer. You can download it from Python's official website.

Core Concept

Python's web development capabilities are primarily driven by its extensive library ecosystem. One of the most popular libraries for building web applications is Flask, a micro web framework that provides an easy-to-use interface for creating web pages and APIs.

Introduction to Flask

Flask is a lightweight web framework for Python that makes it easy to build web applications quickly and efficiently. It requires minimal setup and offers a clean, simple API for handling requests and responses. To get started with Flask, first install it using pip:

pip install flask

Creating a Simple Flask Application

Now let's create a simple Flask application to serve a static HTML page. Create a new file called app.py and add the following code:

from flask import Flask, render_template

app = Flask(__name__)

@app.route('/')
def home():
return render_template('index.html')

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

This code creates a new Flask application, sets up a route for the home page (/), and tells it to render an index.html file when that route is accessed. When you run this script with python app.py, your web browser should automatically open to http://127.0.0.1:5000/, displaying the contents of index.html.

Creating an HTML Template for Your Webpage

Next, let's create the HTML file for our webpage. Create a new folder called templates alongside app.py and add an index.html file inside it with the following content:

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>My First Webpage</title>
</head>
<body>
<h1>Welcome to My First Webpage!</h1>
</body>
</html>

This HTML file defines a basic web structure, including the document type (`), head (), body (), and title () elements. The ` tag contains the main heading for our webpage.

Worked Example

Let's create a simple Flask application that allows users to submit their names through a form and displays them on the webpage.

Step 1: Create a new file called `names.html` in the `templates` folder with the following content:

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>My Webpage with Names</title>
</head>
<body>
<h1>Names Submitted:</h1>
{% if names %}
<ul>
{% for name in names %}
<li>{{ name }}</li>
{% endfor %}
</ul>
{% else %}
<p>No names submitted yet.</p>
{% endif %}
<form action="/submit" method="post">
<label for="name">Enter your name:</label>
<input type="text" id="name" name="name">
<button type="submit">Submit</button>
</form>
</body>
</html>

This HTML file creates a list of names submitted by users and displays it when there are names. It also includes a form for users to submit their names.

Step 2: Modify the `app.py` file to handle form submissions and store names:

from flask import Flask, render_template, request, session

app = Flask(__name__)
app.secret_key = "mysecretkey" # Set a secret key for session management

names = []

@app.route('/')
def home():
if 'names' in session:
names = session['names']
return render_template('index.html')

@app.route('/submit', methods=['POST'])
def submit():
name = request.form['name']
names.append(name)
session['names'] = names
return redirect('/')

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

This code modifies the app.py file to handle form submissions by creating a new route (/submit) for handling POST requests. It stores the submitted names in a list and uses session management to keep track of them between page loads.

Common Mistakes

1.1 - Forgetting to import necessary modules (e.g., Flask)

In your Python script, make sure you have imported the Flask module at the beginning:

from flask import Flask, render_template, request, session

1.2 - Not defining the `home()` function or setting up the route for the home page

Ensure that your app.py file contains a home() function and sets up the route for the home page:

@app.route('/')
def home():
if 'names' in session:
names = session['names']
return render_template('index.html')

1.3 - Misconfiguring the form action or method in the HTML file

In your index.html file, make sure that the form action is set to the correct route (e.g., /submit) and uses the correct method (POST):

<form action="/submit" method="post">
...
</form>

1.4 - Not handling form data correctly on the Python side (e.g., using `request.args` instead of `request.form`)

In your Python script, make sure you are accessing form data using request.form['name'] instead of request.args.get('name').

1.5 - Forgetting to close the Flask application with `app.run(debug=True)` at the end of the script

Always remember to run your Flask application using app.run(debug=True) at the bottom of your script:

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

Practice Questions

Modify the example to display a list of user-submitted names on the webpage.
Add validation to ensure that only alphabetic characters are entered for the name.
Create a new route to display information about a specific book (e.g., title, author, and description).
Modify the example to allow users to submit multiple names separated by commas.
Implement a login system that requires users to enter a username and password before accessing certain pages.
Create a simple e-commerce store where users can add items to a cart and make purchases.
Design a web application for managing a library, allowing users to search for books, reserve them, and renew their reservations.

FAQ

Q: What is Flask?

A: Flask is a micro web framework for Python that provides an easy-to-use interface for creating web pages and APIs.

Q: How do I run my Flask application?

A: To run your Flask application, save your app.py file and any associated templates in the same directory, then execute the following command in your terminal or command prompt: python app.py.

Q: What is the difference between GET and POST requests?

A: GET requests are used to retrieve data from a server, while POST requests are used to send data to a server (e.g., form submissions).

Q: How do I handle errors in my Flask application?

A: You can create custom error handlers for specific exceptions or use the built-in app.errorhandler() function to handle common errors like 404 Not Found and 500 Internal Server Error.

Q: How do I deploy my Flask application?

A: There are several ways to deploy a Flask application, including using cloud services like Heroku or AWS Elastic Beanstalk, or setting up your own server with tools like Gunicorn and Nginx.