Error message:

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/flask/", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python2.7/dist-packages/flask/", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/usr/local/lib/python2.7/dist-packages/flask/", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/dist-packages/flask/", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/", line 1478, in full_dispatch_request
    response = self.make_response(rv)
  File "/usr/local/lib/python2.7/dist-packages/flask/", line 1566, in make_response
    raise ValueError('View function did not return a response')
ValueError: View function did not return a response

And my code:

#Used for starting the flask server
from flask import Flask #Import flask mains
from flask import request #Import flask requests
from flask import render_template #Import flask render templates
import json, urllib #import api modules
import time #Imporing time in darlek voice
app = Flask(__name__)

def my_form():
    return render_template("my-form.html") #Set render template

@app.route("", methods=['POST'])
def my_form_post():
    openwindow_at = float(request.form['open']) #When it reached ? open window
    if request.form['scale'] == "kelvin": #Change figures
        print("Do nothing") #Debug info
    elif request.form['scale'] == "celcius":
        openwindow_at = openwindow_at + int(273.15) #celcius to kelvin
    elif request.form['scale'] == "fah": #Fah to kelvin
        openwindow_at = (openwindow_at + 459.67) * 5 / 9  #F to kelvin
    text = request.form['text'] #Get info from First page
    url = "" + text #Download the json
    response = urllib.urlopen(url) #Download Json
    data = json.loads( #Parse json
    print("Current Weather in " + text + " " + data['weather'][0]['description']) #Debug infomation
    print("Temp: " + str(data['main']['temp'])) #Print temp 

    if data['weather'][0]['description'].find("rain") >= 0: #Check The weather
        return "Shutting your window"
        Close the window(Tom's job)
    if float(data['main']['temp']) >= openwindow_at:
        return "Opening your window"
        #open the window (Tom's job)
if __name__ == '__main__':
    app.debug = True #Uncomment to enable debugging #Run the Server

and my-form.html is:

<!DOCTYPE html>
<html lang="en">
    <h1>Enter a place</h1>
    <form action="." method="POST">
        <input type="text" name="text">
        <input type="submit" name="my-form" value="Send">
    <p>Open window if temp is greater than<input type="textbox" name="open"></input> <input type="radio" name="scale" value="kelvin">Kelvin</input><input type="radio" name="scale" value="celcius">Celcius</input><input type="radio" name="scale" value="fah">FarenHeit</input></p>

If I put a while loop there it loads for ever.

Then enter a temp higher than the current one the page loads forever.
And if I use the current code listed above it gives the error.

The following does not return a response:

You must return anything like return afunction() or return 'a string'.

This can solve the issue

You are not returning a response object from your view my_form_post. The function ends with implicit return None, which Flask does not like.

Make the function my_form_post return an explicit response, for example

return 'OK'

at the end of the function.