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Build a URL shortener

Written by

Bernardo Palos

in

Here’s a simple URL shortener implementation using Python (Flask) and SQLite. It allows users to input long URLs and get a short code they can use to redirect to the original URL.

🔧 Tech Stack:

  • Python

  • Flask (web framework)

  • SQLite (lightweight database)

  • Hashlib (to create short codes)

📁 Project Structure:

cpp
url_shortener/
│
├── app.py
├── templates/
│   ├── index.html
│   └── redirect.html
└── shortener.db  (auto-created)

app.py – Main Flask Application

python
from flask import Flask, request, redirect, render_template, url_for
import sqlite3
import hashlib

app = Flask(__name__)
DB = 'shortener.db'

def init_db():
    with sqlite3.connect(DB) as conn:
        conn.execute('''
            CREATE TABLE IF NOT EXISTS urls (
                id INTEGER PRIMARY KEY AUTOINCREMENT,
                original TEXT NOT NULL,
                short TEXT NOT NULL UNIQUE
            )
        ''')
init_db()

def generate_short_code(url):
    return hashlib.md5(url.encode()).hexdigest()[:6]

@app.route('/', methods=['GET', 'POST'])
def index():
    short_url = None
    if request.method == 'POST':
        original_url = request.form['url']
        short_code = generate_short_code(original_url)
        short_url = request.host_url + short_code

        with sqlite3.connect(DB) as conn:
            cur = conn.cursor()
            cur.execute("SELECT * FROM urls WHERE short = ?", (short_code,))
            data = cur.fetchone()
            if not data:
                cur.execute("INSERT INTO urls (original, short) VALUES (?, ?)", (original_url, short_code))
                conn.commit()
    return render_template('index.html', short_url=short_url)

@app.route('/<short_code>')
def redirect_to_original(short_code):
    with sqlite3.connect(DB) as conn:
        cur = conn.cursor()
        cur.execute("SELECT original FROM urls WHERE short = ?", (short_code,))
        result = cur.fetchone()
        if result:
            return redirect(result[0])
        else:
            return render_template('redirect.html', message="Invalid or expired short URL.")

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

templates/index.html

html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>URL Shortener</title>
</head>
<body>
    <h1>Simple URL Shortener</h1>
    <form method="POST">
        <input type="url" name="url" placeholder="Enter long URL" required>
        <button type="submit">Shorten</button>
    </form>

    {% if short_url %}
        <p>Your shortened URL: <a href="{{ short_url }}" target="_blank">{{ short_url }}</a></p>
    {% endif %}
</body>
</html>

templates/redirect.html

html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>URL Not Found</title>
</head>
<body>
    <h1>{{ message }}</h1>
    <a href="/">Go back</a>
</body>
</html>

✅ How to Run

  1. Save files in a folder url_shortener/.

  2. Install Flask: pip install flask

  3. Run the app: python app.py

  4. Visit http://127.0.0.1:5000/ in your browser.

This simple tool generates a 6-character MD5-based short code for any URL and saves it in a SQLite DB. You can further enhance it with custom aliases, user auth, expiration, or analytics.

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