from threading import Thread
from Queue import Queue
from Tkinter import Tk, Label, Button, Entry, Text, END, DISABLED, NORMAL
import time

requests = Queue()
responses = Queue()

def logic():
    while True:
        gui_print("Enter three numbers.")
        a = get_gui_input("first number:")
        b = get_gui_input("second number:")
        c = get_gui_input("third number:")
        gui_print("Calculating...")
        time.sleep(2)
        gui_print("their sum is {}".format(int(a)+int(b)+int(c)))
        if get_gui_input("Continue?").lower() == "n":
            break

def gui_print(s):
    requests.put(("print", s))

def get_gui_input(prompt=""):
    requests.put(("input", prompt))
    return responses.get()


business_logic = Thread(target=logic)
business_logic.daemon = True
business_logic.start()

def idle():
    if not requests.empty():
        kind, s = requests.get()
        if kind == "print":
            print_area.insert('end', s + "\n")
        elif kind="input":
            input_prompt_label.config(text=s)
            button.config(state=NORMAL)
        else:
            raise Exception("Unknown request type {}".format(kind))
    if business_logic.is_alive():
        root.after(100, idle)
    else:
        root.destroy()

def clicked():
    text = response_entry.get()
    print_area.delete('1.0', END)
    response_entry.delete(0, END)
    responses.put(text)
    input_prompt_label.config(text="")
    button.config(state=DISABLED)

root = Tk()

print_area = Text(root, height=10)
print_area.pack()

input_prompt_label = Label(root)
input_prompt_label.pack()

response_entry = Entry(root)
response_entry.pack()

button = Button(root, text="submit", command=clicked, state=DISABLED)
button.pack()

root.after(100, idle)
root.mainloop()