How to wait for a server response without freezing the tkinter GUI

Question

I am making a tkinter GUI that requests information to a server that takes some time to respond. I really don't know how to tell tkinter to wait for the response in a clever way so that the window loop doesnt freeze.

What I want to achieve is to make the popup window responsive, and to see the animation of the progressbar. I don't really know if it helps but I intend to use this GUI on Windows.

Here is my code: (I used time.sleep to simulate sending and recieving from a server)

import tkinter as tk
import tkinter.ttk as ttk
import time


def send_request(data):
    # Sends request to server, manages response and returns it
    time.sleep(10)


class Window(tk.Toplevel):
    def __init__(self, root, *args, **kargs):
        super().__init__(root, *args, **kargs)
        # Options of the window
        self.geometry("500x250")
        self.resizable(False, False)
        self.grab_set()
        # Widgets of the window
        self.button = tk.Button(self, text="Send Request", command=self.start_calc)
        self.button.pack()
        self.bar = ttk.Progressbar(self, orient = "horizontal", mode= "indeterminate")
        self.bar.pack(expand=1, fill=tk.X)

    def start_calc(self):
        # Prepares some data to be send
        self.data_to_send = []
        # Start bar
        self.bar.start()
        # Call send request
        self.after(10, self.send_request_and_save_results)

    def send_request_and_save_results(self):
        # Send request with the data_to_send
        result = send_request(self.data_to_send)
        # Save results
        # Close window
        self.quit()
        self.destroy()


class App:
    def __init__(self, root):
        self.root = root
        self.button = tk.Button(root, text="Open Window", command=self.open_window)
        self.button.pack()

    def open_window(self):
        window = Window(self.root)
        window.mainloop()


root = tk.Tk()
root.geometry("600x300")
app = App(root)
root.mainloop()

Answer 1

I came up with this solution:

import tkinter as tk
import tkinter.ttk as ttk
import time
from threading import Thread


def send_request_and_save_results(data, flag):
    # This is called in another thread so you shouldn't call any tkinter methods
    print("Start sending: ", data)
    time.sleep(10)
    print("Finished sending")

    # Signal that this function is done
    flag[0] = True


class Window(tk.Toplevel):
    def __init__(self, root, *args, **kargs):
        super().__init__(root, *args, **kargs)
        # Options of the window
        self.geometry("500x250")
        self.resizable(False, False)
        self.grab_set()
        # Widgets of the window
        self.button = tk.Button(self, text="Send Request", command=self.start_calc)
        self.button.pack()
        self.bar = ttk.Progressbar(self, orient="horizontal", mode="indeterminate")
        self.bar.pack(expand=1, fill="x")

    def start_calc(self):
        # Prepares some data to be send
        self.data_to_send = [1, 2, 3]
        # Start bar
        self.bar.start()
        # Call send request
        self.send_request_and_save_results()

    def send_request_and_save_results(self):
        # Create a flag that wukk signal if send_request_and_save_results is done
        flag = [False]
        # Send request with the data_to_send and flag
        t1 = Thread(target=send_request_and_save_results,
                    args=(self.data_to_send, flag))
        t1.start()
        # A tkinter loop to check if the flag has been set
        self.check_flag_close_loop(flag)

    def check_flag_close_loop(self, flag):
        # if the flag is set, close the window
        if flag[0]:
            self.close()
        # Else call this function again in 100 milliseconds
        else:
            self.after(100, self.check_flag_close_loop, flag)

    def close(self):
        # I am pretty sure that one of these is unnecessary but it
        # depends on your program
        self.quit()
        self.destroy()


class App:
    def __init__(self, root):
        self.root = root
        self.button = tk.Button(root, text="Open Window", command=self.open_window)
        self.button.pack()

    def open_window(self):
        window = Window(self.root)
        window.mainloop()


root = tk.Tk()
root.geometry("600x300")
app = App(root)
root.mainloop()

Notice how all tkinter calls are in the main thread. This is because sometimes tkinter doesn't play nice with other threads.

All I did was call send_request_and_save_results with a flag that the function sets when it is done. I periodically chech that flag in the check_flag_close_loop method, which is actually a tkinter loop.

The flag is a list with a single bool (the simplest solution). That is because python passes mutable objects by reference and immutable objects by value.