import tkinter
import paho.mqtt.client as mqtt

def button_action():
    temp = entry.get()
    client = mqtt.Client('demo_unimib_pubxsws')
    client.connect('test.mosquitto.org')
    client.publish('skenz_room1/temperature', temp)


win = tkinter.Tk()
entry = tkinter.Entry(win)
entry.pack(side=tkinter.LEFT)

button = tkinter.Button(win, text="Send!", command=button_action)
button.pack(side=tkinter.RIGHT)

win.mainloop()