Race condition in Python

Race condition in Python

I am trying to teach my students about race conditions on the web, and for that purpose, I am using a simple bank example, in which we transfer an amount from person A to Person B's account. If we use Burp and send simultaneous requests like 20-30 that add operation will complete; however, the subtract operation will complete later. So If person A has $20 and Person B has $0. Once I send a transfer request for $20 from A to B (20 simulatnours request), there is a chance that Person B account will get $20 more than once.. Here is my code

  if user['balance'] >= amount:

        # Credit the target user's account
        conn.execute('UPDATE users SET balance = balance + ? WHERE account_number = ?', 
                     (amount, target_account_number))
        conn.close()  # Immediately close connection to force an early write

        # Simulate a delay to allow race condition
        import time
        time.sleep(2)  # Simulate delay

        # Open a new connection for the debit operation
        conn = get_db()

        # Debit the sender's account
        conn.execute('UPDATE users SET balance = balance - ? WHERE account_number = ?', 
                     (amount, session['user']))
        conn.close()  # Close connection to apply the change immediately

        flash(f'Success! Transferred ${amount} to account {target_account_number}.')
    else:
        flash('Insufficient funds.')

    return redirect(url_for('dashboard'))

Is there anything that I am doing wrong for race conditions? my backend is SQLITE