Flask

3.1.3 · active · verified Sat Mar 28

Flask is a lightweight WSGI web application framework in Python, designed with simplicity and flexibility in mind. The current version is 3.1.3, released on March 28, 2026, following a regular release cadence with feature and fix updates as needed.

Warnings

breaking Flask 3.1.3 includes a security fix that may affect session behavior. Review the release notes for details.
Fix: Update your Flask application to handle session changes introduced in version 3.1.3.
gotcha Relative imports can cause issues if not used correctly. Ensure your project structure supports them to avoid ImportError.
Fix: Use absolute imports or adjust your project structure to support relative imports properly.

Install

pip install flask Install Flask

Imports

Flask
```
from flask import Flask
```
Ensure 'flask' is installed in your environment; otherwise, you'll encounter an ImportError.
render_template
```
from flask import render_template
```
Used for rendering HTML templates; requires Jinja2.
request
```
from flask import request
```
Provides access to request data; ensure 'werkzeug' is installed.

Quickstart

A minimal Flask application that renders an 'index.html' template when accessing the root URL.

from flask import Flask, render_template, request

app = Flask(__name__)

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

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

view raw JSON →