hello.py

import os
from flask import Flask, render_template,request
import random

app = Flask(__name__)


nucleotide = ["A","G","T","C"]

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

@app.route('/', methods=['POST'])
def hello1():
    if int(request.form['len']) < 1:
        return render_template("index.html", error="Number has to be greater than 0")

    if int(request.form['len']) > 1000000:
        return render_template("index.html", error="Number has to be less than 1,000,000")
     
    len = request.form['len']
    seq = ''.join([random.choice(nucleotide)
               for nuc in range(int(len))])
    rev_seq = seq[::-1]
    rev_seq = rev_seq.replace("A","t").replace("T","a").replace("G","c").replace("C","g").upper()
    # processed_text = text.upper()
    x = 1
    return render_template("index.html", seq = seq , rev_seq = rev_seq , x=x)

@app.errorhandler(404)
def page_not_found(e):
    return render_template('404.html'), 404

if __name__ == '__main__':
    port = int(os.environ.get("PORT", 5000))
    app.run(host='0.0.0.0', port=port, debug="True")