tcl_async_demo.py

from tkinter import *
import asyncio
from functools import wraps
import websockets

def runloop(func):
    '''
    This decorator converts a coroutine into a function which, when called,
    runs the underlying coroutine to completion in the asyncio event loop.
    '''
    func = asyncio.coroutine(func)
    @wraps(func)
    def wrapper(*args, **kwargs):
        return asyncio.get_event_loop().run_until_complete(func(*args, **kwargs))
    return wrapper

@asyncio.coroutine
def run_tk(root, interval=0.05):
    '''
    Run a tkinter app in an asyncio event loop.
    '''
    try:
        while True:
            root.update()
            yield from asyncio.sleep(interval)
    except TclError as e:
        if "application has been destroyed" not in e.args[0]:
            raise

@asyncio.coroutine
def listen_websocket(url):
    '''
    Connect to a websocket url, then print messages received on the connection
    until closed by the server.
    '''
    ws = yield from websockets.connect(url)
    while True:
        msg = yield from ws.recv()
        if msg is None:
            break
        print(msg)

@runloop
def main():
    root = Tk()
    entry = Entry(root)
    entry.grid()
    
    def spawn_ws_listener():
        return asyncio.async(listen_websocket(entry.get()))

    Button(root, text='Print', command=spawn_ws_listener).grid()
    
    yield from run_tk(root)

if __name__ == "__main__":
    main()

Right. I just wanted to see how tkinter runs "as intended" in the MacOS environment.

Yep, that's a goofy-looking unfortunate graph, haha.

I think I've figured it out. This page at tkdocs tells of bad things that happen with the elderly version of Tcl/Tk included with MacOs.
https://tkdocs.com/tutorial/install.html
They say to not use this version (typically 8.5) but instead to install the latest 8.6 (8.6.9 now). But, if you install Python with homebrew, there is currently no easy way to point it to a newly installed version of Tk. At this point in my research, the only way to get the updated Tcl/Tk to work with Python3 is to install Python without homebrew. Anyway, I've run the tk_sync_demo.py code (that I posted previously) on a Mac with Python 3.7.3 AND Tk version 8.6. Memory runs flatline. So, it looks like my intention of simplifying cross platform support by using a built-in library for the GUI (instead of PyQt5) is not as flawless as I had hoped.

Aww man, that's a bummer. Glad you found the culprit, though!