Let's start by introducing Flask, as we will be using it as an example in all the modules of this section. If you are not familiar with Python programming yet, take the Hakatemian 

Flask is a lightweight and flexible web framework designed to facilitate the development of web applications using the Python programming language. Flask provides a foundation for creating web applications that are easy to understand and maintain. It is a popular choice among many developers as it offers many features that make web development fast and efficient. Flask is also an open-source project, which means that developers can benefit from the contributions of the community and share their experiences with others. This makes Flask a very user-friendly framework suitable for both beginners and experienced developers.


This program creates a web application that displays the "Hello, Hakatemia!" heading when the user visits the root directory of the application.

The first line of the program loads Flask. The next line creates a new instance of the Flask application named "

 tells Flask how to find the application in the file structure, you don't need to worry about that now.

The first line of the code determines the initial 

 decorator. This decorator tells Flask that the function handles HTTP requests with the path 

 function is defined, which returns an HTML document:

Finally, the Flask development server is started, which listens on port 81.

Let's start by introducing Flask, as we will be using it as an example in all the modules of this section. If you are not familiar with Python programming yet, take the Hakatemian [Python programming course](/courses/python-ohjelmointi) before continuing from here.

## What is Flask?

Flask is a lightweight and flexible web framework designed to facilitate the development of web applications using the Python programming language. Flask provides a foundation for creating web applications that are easy to understand and maintain. It is a popular choice among many developers as it offers many features that make web development fast and efficient. Flask is also an open-source project, which means that developers can benefit from the contributions of the community and share their experiences with others. This makes Flask a very user-friendly framework suitable for both beginners and experienced developers.

---

## Simple example

Here is a simple Flask program:

```python
from flask import Flask app = Flask(__name__) @app.route(&#39;/&#39;) def hello_world(): return &#39;<h1> Hello, Hakatemia!</h1> &#39; app.run(host=&#39;0.0.0.0&#39;, port=81)
```

This program creates a web application that displays the "Hello, Hakatemia!" heading when the user visits the root directory of the application.

The first line of the program loads Flask. The next line creates a new instance of the Flask application named "**app**". **\_\_name\_\_** tells Flask how to find the application in the file structure, you don't need to worry about that now.

The first line of the code determines the initial *route* ("/") of the application using the **@app.route** decorator. This decorator tells Flask that the function handles HTTP requests with the path **/** (in practice, the homepage).

On the fourth line, the **hello\_world** function is defined, which returns an HTML document:

```html
<h1>Hello, Hakatemia!</h1>
```

Finally, the Flask development server is started, which listens on port 81.

---

## Practice

@embed 958a99dba4c7


Python and Flask

This course is an introduction to web development and focuses on the basics of HTML, CSS, JavaScript and backend systems. The aim of the course is to provide students with the necessary skills and knowledge to design, develop and understand simple web applications.

This course is an introduction to web development and focuses on the basics of building websites, namely HTML, CSS, JavaScript, and fundamentals of backend systems. The goal of the course is to provide you with the necessary skills and knowledge to design and develop simple full-stack web applications, as well as understand web applications made by others.

In the first part, HTML is studied, which is a markup language used in building websites.


The second part covers the basics of CSS, such as the use of style sheets, rules, selectors, and formatting. It also covers advanced features of CSS, such as animations and responsive design.

In the third part, we will study JavaScript, which is currently an incredibly important tool in both frontend and backend development, and thus also in cybersecurity and ethical hacking.

In the final part, we will learn how to build back-end systems using the Python Flask framework. You will learn the basics of back-end systems, such as using databases, authentication, session management, and access control.

You can do the course exercises on your own computer if you want, but each code example has a button that allows you to directly run the code in the browser and see what the page looks like or what the script prints. So you do not need to install anything, but you can if you want.

It is recommended but optional to create an account on replit.com service. In that case, you can just click "Fork" on the code examples to make a copy for yourself to play with

Python and Flask

What is Flask?

Learn to hack — start here