Python tkinter async mainloop

tkinter_async_helper.py

import asyncio, tkinter
import ctypes
import math
import threading
from types import coroutine

__all__ = ["ATk"]

if tkinter.TclVersion == 8.6:
    try:
        # Windows
        _tcl = ctypes.CDLL("tcl86t")
        _tk = ctypes.CDLL("tk86t")
    except FileNotFoundError:
        # Mac & Linux
        _tcl = ctypes.CDLL("libtcl8.6") # FIXME: actually test on Mac and/or Linux
        _tk = ctypes.CDLL("libtk8.6") # FIXME: actually test on Mac and/or Linux

elif tkinter.TclVersion == 9.0:
    # FIXME: Tcl/Tk 9.0 added much better asynchronous APIs
    try:
        # Windows
        _tcl = ctypes.CDLL("tcl90t")
        _tk = ctypes.CDLL("tk90t")
    except FileNotFoundError:
        # Mac & Linux
        _tcl = ctypes.CDLL("libtcl9.0") # FIXME: actually test on Mac and/or Linux
        _tk = ctypes.CDLL("libtk9.0") # FIXME: actually test on Mac and/or Linux

else:
    raise NotImplementedError(f"Tcl/Tk {tkinter.TclVersion} not supported yet")

Tcl_WaitForEvent = _tcl["Tcl_WaitForEvent"]
Tk_GetNumMainWindows = _tk["Tk_GetNumMainWindows"]

class Tcl_Time(ctypes.Structure):
    _fields_ = [
        ("sec", ctypes.c_long),
        ("usec", ctypes.c_int),
    ]

    @classmethod
    def fromseconds(cls, seconds):
        usec = int(math.ceil(seconds * 1_000_000))
        sec, usec = divmod(usec, 1_000_000)
        assert 0 <= sec <= 2_147_483_647
        assert 0 <= usec < 1_000_000
        return cls(sec=sec, usec=usec)


class ATk(tkinter.Tk):
    @coroutine
    def mainloop_async(self, *, _tcl8_MaxBlockTime=None):
        # https://www.tcl-lang.org/man/tcl8.6/TclLib/Notifier.htm#:~:text=event%20sources%20that%20need%20to%20poll%20for%20events,force%20the%20external%20event%20loop%20to%20call%20Tcl
        if _tcl8_MaxBlockTime is None:
            # WARNING: INFINITE BLOCK TIME HANGS NON-TK EVENTS WHENEVER USER IS IDLE
            timeout_ = ctypes.c_void_p(None)
        else:
            # WARNING: NONZERO BLOCK TIME STUTTERS NON-TK EVENTS WHENEVER USER IS IDLE
            # WARNING: ZERO BLOCK TIME WASTES A LOT OF CPU WITH AGGRESSIVE BUSY-POLL
            timeout = Tcl_Time.fromseconds(_tcl8_MaxBlockTime)
            timeout_ = ctypes.pointer(timeout)

        # https://github.com/python/cpython/blob/v3.14.0rc2/Modules/_tkinter.c#L2866-L2877
        # https://github.com/tcltk/tk/blob/core-8-6-14/generic/tkEvent.c#L2108
        # https://github.com/tcltk/tcl/blob/core-8-6-14/generic/tclNotify.c#L946
        self_update = self.update
        result = Tcl_WaitForEvent(ctypes.pointer(Tcl_Time.fromseconds(0)))
        while result != -1 and Tk_GetNumMainWindows() > 0:
            if result > 0:
                self_update()

            yield

            result = Tcl_WaitForEvent(timeout_)

    def mainloop(self, coro=None):
        if coro is None:
            super().mainloop()
            return

        raise NotImplementedError("buddy coroutine support not implemented yet. If using Python 3.11+, consider manually combining ATk.mainloop_async with asyncio.TaskGroup")


async def main():
    # demo h/t https://github.com/python/cpython/blob/v3.14.0rc1/Lib/tkinter/__init__.py#L4972
    import tkinter.ttk as ttk

    root = ATk()
    text = "This is Tcl/Tk %s" % root.globalgetvar('tk_patchLevel')
    text += "\nThis should be a cedilla: \u00e7"
    label = ttk.Label(root, text=text)
    label.pack()
    test = ttk.Button(root, text="Click me!",
              command=lambda root=root: root.test.configure(
                  text="[%s]" % root.test['text']))
    test.pack()
    root.test = test
    quit = ttk.Button(root, text="QUIT", command=root.destroy)
    quit.pack()

    root.iconify()
    root.update()
    root.deiconify()

    await root.mainloop_async() # <- WOW!


if __name__ == '__main__':
    asyncio.run(main())