Building a URL Redirector in Python for Dynamic QR Codes

If you print 1,000 posters with a QR code and the website URL changes next week, a "Static" QR code becomes a pile of wasted paper. The solution is a Dynamic QR code.

Instead of encoding your final destination (like myshop.com/promo-january), you encode a "Short URL" that you control (like myqr.link/offer). When a user scans it, your server looks up where offer should go today and redirects them instantly.

1. The Architecture of a Dynamic System

A dynamic system requires three parts:

1. The Database: Stores the "Key" (e.g., offer) and the "Target" (e.g., myshop.com/promo).
2. The Redirector: A small web server (Flask) that listens for scans.
3. The Generator: A script that points the QR code to your server.

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2. The Backend: Flask + SQLite

We will use Flask to handle the web traffic and SQLite to manage our links.

from flask import Flask, redirect, abort
import sqlite3

app = Flask(__name__)

def get_target_url(slug):
    """Lookup the destination URL from our database."""
    conn = sqlite3.connect("links.db")
    cursor = conn.cursor()
    cursor.execute("SELECT target FROM redirects WHERE slug=?", (slug,))
    result = cursor.fetchone()
    conn.close()
    return result[0] if result else None

@app.route('/<slug>')
def dynamic_redirect(slug):
    """The 'Entry Point' for the QR code."""
    target = get_target_url(slug)
    if target:
        # 302 redirect means 'Found/Temporary'
        # This tells browsers not to cache the destination
        return redirect(target, code=302)
    else:
        return abort(404)

if __name__ == '__main__':
    app.run(port=5000)

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3. The Generator: Pointing to the Redirector

When you generate the QR code, you no longer use your final website address. You use your server's address.

import qrcode

# Your server address (for local testing)
SERVER_BASE = "[http://127.0.0.1:5000/](http://127.0.0.1:5000/)"
LINK_KEY = "winter_sale"

# This code stays the same forever!
qr_data = f"{SERVER_BASE}{LINK_KEY}"
img = qrcode.make(qr_data)
img.save("dynamic_qr.png")

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4. Updating the Destination

To change where the code points, you simply run a SQL command. You do not need to regenerate the image.

-- To update the destination from old_site.com to new_site.com:
UPDATE redirects 
SET target = '[https://newsite.com/february-deals](https://newsite.com/february-deals)' 
WHERE slug = 'winter_sale';

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📑 Why This is Professional-Grade

Feature	Static QR	Dynamic QR
Editing	Impossible after printing	Unlimited updates anytime
Tracking	Basic (via UTMs only)	Advanced (Time, Location, Device)
Scan Speed	Dense (long URLs slow scan)	Clean (short URLs scan faster)
Cost	Free / One-time	Requires hosting / Database

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📚 Sources & Technical Refs

• [3.2] TechBeamers: How to Create Dynamic QR Code in Python - In-depth guide on the redirection logic.
• [4.3] Hovercode Blog: What is a Dynamic QR code? - Excellent conceptual explanation of the "Redirect Link" vs "Direct Link."
• [1.1] Flask Documentation: Redirects and Errors - Best practices for HTTP 302 status codes.