Python asyncio with Tkinter.

Look at this function:

def calculate_sync(self):
    max = 3000000
    for i in range(1, max):
        self.progressbar["value"] = i / max * 100

When this function is executed synchronously, the GUI freezes.

Blocking and freezing the UI

By clicking the 'Calculate Sync' button, the function is called and the GUI freezes. After a few seconds, the progress bar is 100% full and the GUI gets responsive again.

But what you want, is that the function runs while updating the UI.

Non-blocking

This time, the 'Calculate Async' button is clicked and the function executes asynchronously and the GUI stays responsive.

Solution

The following code creates an app that creates a window. The window gets the asyncio event loop.

__init__ creates a window and the show function creates an infinite loop that calls self.root.update(). update() keeps the GUI event loop running.

import tkinter as tk
from tkinter import ttk
import asyncio


class App:
    async def exec(self):
        self.window = Window(asyncio.get_event_loop())
        await self.window.show();


class Window(tk.Tk):
    def __init__(self, loop):
        self.loop = loop
        self.root = tk.Tk()
        self.animation = "░▒▒▒▒▒"
        self.label = tk.Label(text="")
        self.label.grid(row=0, columnspan=2, padx=(8, 8), pady=(16, 0))
        self.progressbar = ttk.Progressbar(length=280)
        self.progressbar.grid(row=1, columnspan=2, padx=(8, 8), pady=(16, 0))
        button_block = tk.Button(text="Calculate Sync", width=10, command=self.calculate_sync)
        button_block.grid(row=2, column=0, sticky=tk.W, padx=8, pady=8)
        button_non_block = tk.Button(text="Calculate Async", width=10, command=lambda: self.loop.create_task(self.calculate_async()))
        button_non_block.grid(row=2, column=1, sticky=tk.W, padx=8, pady=8)

    async def show(self):
        while True:
            self.label["text"] = self.animation
            self.animation = self.animation[1:] + self.animation[0]
            self.root.update()
            await asyncio.sleep(.1)

    def calculate_sync(self):
        max = 3000000
        for i in range(1, max):
            self.progressbar["value"] = i / max * 100

    async def calculate_async(self):
        max = 3000000
        for i in range(1, max):
            self.progressbar["value"] = i / max * 100
            if i % 1000 == 0:
                await asyncio.sleep(0)

asyncio.run(App().exec())

There is no need to install any third party library. Copy and paste this code and run it with Python to test it yourself.