server.py

from flask import Flask, render_template, request, redirect
import csv
app = Flask(__name__)
#print(__name__)

@app.route('/')
def my_home():
    return render_template('index.html')

@app.route('/<string:page_name>')
def htmlpage(page_name):
    return render_template(page_name)

def write_to_csv(data):
    with open('./database.csv', 'a', newline='') as database2:
        email = data["email"]
        subject = data["subject"]
        message = data["message"]
        csv_writer = csv.writer(database2,delimiter=',')
        csv_writer.writerow([email,subject,message])

@app.route('/submit_form', methods=['POST', 'GET'])
def submit_form():
    if request.method == "POST":
        data = request.form.to_dict()
        write_to_csv(data)
        return redirect('/thankyou.html')
    else:
        return "something went wrong, Try again."