What Is Flask?

Flask is a lightweight, open-source Python web framework designed for building web applications quickly and with minimal setup. Built on the WSGI standard and using the Jinja2 templating engine, Flask offers flexibility, modularity and simplicity, making it a popular choice for both beginners and experienced developers who want full control over their application’s architecture without the overhead of a full-stack framework.

Flask is known as a micro-framework, meaning it includes only the core tools needed to build a web application. This leaves most architectural decisions up to the developer, unlike full-stack frameworks like Django that come with built-in features and conventions.

Is Flask Hard to Learn?

Flask is not considered difficult to learn and serves as a strong entry point into Python web development. The Flask documentation is extensive, beginner-friendly and supported by tutorials at all levels, helping developers progress from basic projects to real-world applications.

The documentation also explains the design decisions behind Flask, offering transparency into its development philosophy and enabling contributors to evaluate whether they want to engage with Flask or other Pocoo projects.

Flask vs. Django

Flask is often chosen for lightweight API development, while Django, paired with Django REST Framework, is better suited for larger, more structured APIs. Both frameworks support dynamic HTML rendering using template engines like Jinja2.

As a micro-framework, Flask gives developers more flexibility in how they structure their code, unlike Django, which follows a more prescriptive design. Some Flask apps can be written in a single file.

A typical Flask project typically consists of a folder layout that includes two main folders:

• flaskr/: The main application directory.
• tests/: A directory for test modules.

Additional folders may be added for version control, virtual environments or deployment tooling, depending on the project’s complexity.

RelatedPseudocode: What It Is and How to Write It

Flask Examples

“Hello World!” in Flask Example

Let’s implement a simple “Hello World” web page using Flask. You’ll only need the following seven lines of code.

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World!'

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

Building a simple “Hello World!” web page in Flask is quite simple.

Flask Application Examples

Once you’ve got the Flask basics, you can work toward creating full-featured web applications including: 

• A video chat app with Flask as its backend that uses JavaScript and Twilio to work on all platforms, from a simple web browser to iOS and Android devices.
• A Docker-based microservices that uses both Flask and React to help you understand the fundamentals of general web development, Flask and front-end development.
• Flask can serve as the backend for an attendance system that incorporates facial recognition models via third-party libraries like OpenCV or deep learning APIs.
• If you are a traveler, you can use Flask and Mapbox to make beautiful visualizations of your next trip.
• If you’re just getting started with programming, you can use Flask to build a simple email application.

History of Flask

Armin Ronacher developed Flask and released it in 2010. He led an international group of Python enthusiasts called Pocoo, which also created the Werkzeug WSGI toolkit and the Jinja2 template engine that Flask is built on.

Core technologies of the Flask framework include:

• WSGI (Web Server Gateway Interface) is the commonly used Python web application development standard that defines the interactions between web servers and web applications.
• Werkzeug is a toolkit that uses WSGI to implement, send requests and handle responses. 
• Jinja2 is a Python web template that enables users to combine a template with a data source to render dynamic web pages.

Frequently Asked Questions