.update() is considered to be harmful, try to reimplement with running asyncio loop in a separate thread about async-tkinter-loop

[insolor]

@rdbende thank you, I used dooneevent in my code. I tried your idea of running the loop until dooneevent returns 0, but in reality dooneevent returns 0 most of the times, except when there are some pending events. So instead I used a nested while root.dooneevent(_tkinter.DONT_WAIT) > 0: loop to process all pending events in one iteration of the outer loop.

async-tkinter-loop/async_tkinter_loop.py

Lines 16 to 26 in 4c8e500

	while True:
	# Process all pending events
	while root.dooneevent(_tkinter.DONT_WAIT) > 0:
	pass
	try:
	root.winfo_exists() # Will throw TclError if the main window is destroyed
	except TclError:
	break
	await asyncio.sleep(0.01)

[rdbende]

So instead I used a nested while root.dooneevent(_tkinter.DONT_WAIT) > 0: loop to process all pending events in one iteration of the outer loop.

Actually, that is what I wanted to say :D

[insolor]

Experimental implementation, see separate_thread branch. It almost works as intended, but tests are faining (it seems that it's because pytest tries to run them in parallel), and I'm not happy that you need to switch asyncio events from a different thread, see start_stop_counter.py

[rdbende]

This is how _tkinter.c implements the mainloop:

https://github.com/python/cpython/blob/f63002755d3b7c0bb2e452f158769f19fcf3b850/Modules/_tkinter.c#L2694-L2724

You can see that it uses the Tcl_DoOneEvent function in the mainloop. Apparently this function is exposed in Tkinter, so it might be useful if you want to avoid the problems caused by update.

A while ago I was thinking about implementing an asynchronous mainloop in Tukaan, and this is what I came up with (transferred to Tkinter):

async def _async_main_loop(root: tkinter.Tk) -> None:
    while root.is_alive:
        root.tk.dooneevent(_tkinter.DONT_WAIT)
        await asyncio.sleep(0)

Though using dooneevent at Python level is a bit slower than Tkinter's actual mainloop.

Edit: It might be an even better approach to run dooneevent until it returns 0 (zero means that there's no more events to process), this way it's almost as fast as an update call.

[insolor]

@rdbende ah, ok, now I see. It seems that I misread that statement, but in the end I implemented it in that way as you said.