app.py

from flask import Flask, render_template, request, redirect
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///todo.db'
db = SQLAlchemy(app)

class Todo(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    task = db.Column(db.String(255))
    done = db.Column(db.Boolean, default=False)

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        task = request.form['task']
        new_todo = Todo(task=task)
        db.session.add(new_todo)
        db.session.commit()

    todos = Todo.query.all()
    return render_template('index.html', todos=todos)

@app.route('/delete/<id>')
def delete(id):
    todo = Todo.query.get(id)
    db.session.delete(todo)
    db.session.commit()
    return redirect('/')

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

index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>To-Do List</title>
</head>
<body>
    <h1>To-Do List</h1>
    <form action="/" method="post">
        <input type="text" name="task" placeholder="Add a new task">
        <input type="submit" value="Add">
    </form>
    <ul>
        {% for todo in todos %}
            <li>
                {{ todo.task }}
                <a href="/delete/{{ todo.id }}">Delete</a>
            </li>
        {% endfor %}
    </ul>
</body>
</html>