Why am I losing the value stored in my variable after form.validate_on_submit()?

Question

I'm creating some sort of referral page like the famous one mentioned on Tim Ferris blog but this one in Flask. I have been testing my code with some print statements to see what was happening in the terminal.

Seems like in main() view I'm losing the value stored in unique_code after form.validate_on_submit(). What is happening behind the scenes to get this kind of behavior?

What I'm trying to accomplish is the following:

If the URL is something like [domain]/referral_url/[random unique string] means like this user was referred by another one. So I grab from the URL the random unique string and pass it to the function view, this way when I record the email of this user within the database I can also store who referred this one.

After validation, unique_code when printing in the terminal, in case I print it after validation, it returns to None (default value). Before validation it returns the given unique_code.

Is this a matter of the scope?

For now the code is not finished. Here you have a piece of my views.

@app.route('/', methods=['GET', 'POST'])
@app.route('/referral_url/<unique_code>', methods=['GET', 'POST'])
def main(unique_code=None):
    form = SubscriptionForm()
    # if I print here unique_code it returns the proper one
    if form.validate_on_submit():
    # after validation unique_code returns to default, None in this case
        # for now if we pass validation we are losing unique_code value, looks like empty despite not being so
        if unique_code == True:

            return unique_code
        else:

            if Subscriber.query.filter_by(email=form.email.data).count() == 0:
                subscriber = Subscriber(email=form.email.data)
                db.session.add(subscriber)
                db.session.commit()

            else:
                subscriber = Subscriber.query.filter_by(email=form.email.data).one()
                session['subscriber'] = form.email.data

            return redirect(url_for('dashboard', unique_code = subscriber.unique_url))



return render_template('subscribe/main.html', form=form, unique_code=unique_code)