Flask

Flask is an open-source, minimal Python web framework maintained by the Pallets Projects. It's the #11 most-used web framework overall, reported in roughly 14.4% of developer surveys. Developers reach for it because it's unopinionated — it gives you routing and request handling and decides almost nothing else for you — which makes it popular for small APIs and projects where the team wants full control over structure and dependencies.

Example

A minimal Flask app maps a URL route to a Python function with a single decorator — no project structure is enforced.

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route("/hello/<name>")
def hello(name):
    return jsonify({"message": f"Hello, {name}!"})

@app.route("/items", methods=["POST"])
def create_item():
    data = request.get_json()
    return jsonify({"created": data["name"]}), 201

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

Getting started

Install Flask into a virtual environment, then run the built-in development server.

# install Flask
pip install flask

# run the dev server (app.py contains `app = Flask(__name__)`)
flask --app app run --debug