What is Flask? A Guide to Python’s Lightweight Web Framework

Flask is one of the most popular micro web frameworks in the Python ecosystem. This article breaks down what Flask is, why it’s used, how it compares to other frameworks, and how to get started with it—even if you’re new to web development.

Table of Contents

  1. Introduction to Flask
  2. Why Use Flask?
  3. Flask vs. Other Web Frameworks
  4. Core Components of Flask
  5. Building a Simple Flask App
  6. Common Use Cases
  7. Tips for Getting Started
  8. Top 5 Frequently Asked Questions
  9. Final Thoughts
  10. Resources

Introduction to Flask

Flask is a micro web framework written in Python. Created by Armin Ronacher in 2010, it was designed to keep things simple while allowing developers to build scalable and maintainable web applications. It comes with the bare essentials: routing, templating, and session management. But beyond that, you’re in control.

Why Use Flask?

Flexibility

Flask gives you the power to build your application your way. There’s no required project layout, no forced ORM (Object Relational Mapper), and no strict dependencies. This flexibility makes Flask a go-to choice for both small projects and large-scale web services.

Minimalism

Being a micro framework, Flask is lightweight. It doesn’t come loaded with tools you might never use. That makes it easier to learn, faster to run, and more transparent when it comes to understanding what your code is doing.

Extensibility

Despite being minimal, Flask is incredibly extensible. With thousands of extensions available—like Flask-SQLAlchemy for databases or Flask-Login for user authentication—you can plug in only what you need.

Flask vs. Other Web Frameworks

Flask vs. Django

Django provides more out of the box but is less flexible. Flask, on the other hand, gives developers more freedom.

Feature Flask Django
Type Micro web framework Full-stack web framework
Ease of Use Very beginner-friendly Moderate learning curve
Project Structure Flexible, developer-defined Opinionated, convention-based
ORM Support Optional (e.g., SQLAlchemy) Built-in Django ORM
Admin Interface None built-in (use extensions) Includes a powerful admin panel
Async Support Limited (experimental/extension-based) Partial as of Django 3.1+
Built-in Tools Minimal (add what you need) Includes forms, auth, middleware, etc.
Use Cases APIs, microservices, lightweight apps Large-scale apps, content-heavy sites
Community Large, active Very large, enterprise-level
Documentation Concise and simple Very comprehensive and in-depth

Flask vs. FastAPI

FastAPI is newer and optimized for performance with async support and automatic API documentation. If you’re building APIs at scale, FastAPI might be better. But Flask is more established, has broader community support, and is easier for beginners.

Feature Flask FastAPI
Type Micro web framework Modern web framework for building APIs
Performance Good Excellent (async & high-speed optimized)
Ease of Use Very beginner-friendly Slightly steeper learning curve
Syntax Style Classic Python (functions & decorators) Python 3.6+ with type hints
Async Support Limited (via extensions or tweaks) Built-in native async support
Data Validation Manual or with extensions Automatic via Pydantic
API Docs Requires setup Auto-generated with Swagger & Redoc
Use Cases General web apps, APIs, prototypes Fast, scalable APIs, microservices
Community Larger, mature Growing rapidly
Documentation Extensive, beginner-focused Very modern, type-safe examples

Core Components of Flask

Routes and Views

In Flask, a route maps a URL to a function. Here’s a basic example:

python

from flask import Flask
app = Flask(__name__)@app.route('/')
def home():
return 'Hello, World!'

Templates

Flask uses Jinja2 as its templating engine, allowing dynamic HTML generation:

html

<!-- templates/home.html -->
<html>
<body>
<h1>Hello, {{ name }}!</h1>
</body>
</html>

python
from flask import render_template

@app.route('/hello/')
def hello(name):
return render_template('home.html', name=name)

Request and Response Objects

Flask provides access to request and response objects for handling input/output:

python
from flask import request
@app.route('/submit', methods=['POST'])
def submit():
data = request.form['data']
return f"You submitted: {data}"

Building a Simple Flask App

1. Install Flask:
bash
pip install Flask

2 Create the App:
python
# app.py
from flask import Flask
app = Flask(__name__)@app.route('/')
def index():
return 'Welcome to Flask!'

3. Run the App:
bash
export FLASK_APP=app
flask run

Your app will be available at http://127.0.0.1:5000/.

Common Use Cases

  • REST APIs
  • Prototyping and MVPs
  • Microservices architecture
  • Educational tools and tutorials

Tips for Getting Started

  • Stick with the basics before exploring extensions
  • Follow Flask’s
  • Use virtual environments to isolate dependencies
  • Popular extensions: Flask-WTF, Flask-Login, Flask-Migrate

Top 5 Frequently Asked Questions

Yes. Flask’s simplicity and clear documentation make it ideal for learning web development.
Absolutely. Flask scales well when structured properly using blueprints and extensions.
No. Flask can also serve full HTML pages using Jinja2 templates.
Flask is minimal and flexible. Django is full-featured and opinionated.
Flask is written in Python and is used to develop Python web applications.

Final Thoughts

Flask stands out because it gives developers both control and simplicity. You’re not locked into one way of doing things, and you can scale your project with only the components you need. Whether you’re building an MVP, learning backend development, or deploying APIs in production, Flask provides a clean, reliable foundation to build on.

Resources

  • Flask Official Docs
  • Flask GitHub Repository
  • Jinja2 Docs
  • Flask Mega-Tutorial by Miguel Grinberg