Use asyncio and Tkinter (or another GUI lib) together without freezing the GUI

Trying to run both event loops at the same time is a dubious proposition. However, since root.mainloop simply calls root.update repeatedly, one can simulate mainloop by calling update repeatedly as an asyncio task. Here is a test program that does so. I presume adding asyncio tasks to the tkinter tasks would work. I checked that it still runs with 3.7.0a2.

"""Proof of concept: integrate tkinter, asyncio and async iterator.Terry Jan Reedy, 2016 July 25"""import asynciofrom random import randrange as rrimport tkinter as tkclass App(tk.Tk):    def __init__(self, loop, interval=1/120):        super().__init__()        self.loop = loop        self.protocol("WM_DELETE_WINDOW", self.close)        self.tasks = []        self.tasks.append(loop.create_task(self.rotator(1/60, 2)))        self.tasks.append(loop.create_task(self.updater(interval)))    async def rotator(self, interval, d_per_tick):        canvas = tk.Canvas(self, height=600, width=600)        canvas.pack()        deg = 0        color = 'black'        arc = canvas.create_arc(100, 100, 500, 500, style=tk.CHORD,                                start=0, extent=deg, fill=color)        while await asyncio.sleep(interval, True):            deg, color = deg_color(deg, d_per_tick, color)            canvas.itemconfigure(arc, extent=deg, fill=color)    async def updater(self, interval):        while True:            self.update()            await asyncio.sleep(interval)    def close(self):        for task in self.tasks:            task.cancel()        self.loop.stop()        self.destroy()def deg_color(deg, d_per_tick, color):    deg += d_per_tick    if 360 <= deg:        deg %= 360        color = '#%02x%02x%02x' % (rr(0, 256), rr(0, 256), rr(0, 256))    return deg, colorloop = asyncio.get_event_loop()app = App(loop)loop.run_forever()loop.close()

Both the tk update overhead and time resolution increase as the interval is decreased. For gui updates, as opposed to animations, 20 per second may be enough.

I recently succeeded in running async def coroutines containing tkinter calls and awaits with mainloop. The prototype uses asyncio Tasks and Futures, but I don't know if adding normal asyncio tasks would work. If one wants to run asyncio and tkinter tasks together, I think running tk update with an asyncio loop is a better idea.

EDIT: A least as used above, exception without async def coroutines kill the coroutine but are somewhere caught and discarded. Silent error are pretty obnoxious.

In a slight modification to your code, I created the asyncio event_loop in the main thread and passed it as an argument to the asyncio thread. Now Tkinter won't freeze while the urls are fetched.

from tkinter import *from tkinter import messageboximport asyncioimport threadingimport randomdef _asyncio_thread(async_loop):    async_loop.run_until_complete(do_urls())def do_tasks(async_loop):    """ Button-Event-Handler starting the asyncio part. """    threading.Thread(target=_asyncio_thread, args=(async_loop,)).start()    async def one_url(url):    """ One task. """    sec = random.randint(1, 8)    await asyncio.sleep(sec)    return 'url: {}\tsec: {}'.format(url, sec)async def do_urls():    """ Creating and starting 10 tasks. """    tasks = [one_url(url) for url in range(10)]    completed, pending = await asyncio.wait(tasks)    results = [task.result() for task in completed]    print('\n'.join(results))def do_freezed():    messagebox.showinfo(message='Tkinter is reacting.')def main(async_loop):    root = Tk()    Button(master=root, text='Asyncio Tasks', command= lambda:do_tasks(async_loop)).pack()    Button(master=root, text='Freezed???', command=do_freezed).pack()    root.mainloop()if __name__ == '__main__':    async_loop = asyncio.get_event_loop()    main(async_loop)

I'm a bit late to the party but if you are not targeting Windows you can use aiotkinter to achieve what you want. I modified your code to show you how to use this package:

from tkinter import *from tkinter import messageboximport asyncioimport randomimport aiotkinterdef do_freezed():    """ Button-Event-Handler to see if a button on GUI works. """    messagebox.showinfo(message='Tkinter is reacting.')def do_tasks():    task = asyncio.ensure_future(do_urls())    task.add_done_callback(tasks_done)def tasks_done(task):    messagebox.showinfo(message='Tasks done.')async def one_url(url):    """ One task. """    sec = random.randint(1, 15)    await asyncio.sleep(sec)    return 'url: {}\tsec: {}'.format(url, sec)async def do_urls():    """ Creating and starting 10 tasks. """    tasks = [        one_url(url)        for url in range(10)    ]    completed, pending = await asyncio.wait(tasks)    results = [task.result() for task in completed]    print('\n'.join(results))if __name__ == '__main__':    asyncio.set_event_loop_policy(aiotkinter.TkinterEventLoopPolicy())    loop = asyncio.get_event_loop()    root = Tk()    buttonT = Button(master=root, text='Asyncio Tasks', command=do_tasks)    buttonT.pack()    buttonX = Button(master=root, text='Freezed???', command=do_freezed)    buttonX.pack()    loop.run_forever()