An example of asynchronous programming with TraitsUI using QT5 backend with Quamash event loop to work with asyncio.

test_traitsui_quamash.py

"""
This code was helpful,
https://stackoverflow.com/questions/32141623/pyqt5-and-asyncio-yield-from-never-finishes
"""
import os
import sys
import quamash
import asyncio
import traceback
import PyQt5
import pdb


# Required setup to get event loop working
app = PyQt5.QtWidgets.QApplication(sys.argv)
loop = quamash.QEventLoop(app)
asyncio.set_event_loop(loop)
loop.set_debug(True)  # optional


# Select QT5
# https://github.com/enthought/traitsui/issues/407
os.environ["ETS_TOOLKIT"] = "qt"
os.environ["QT_API"] = "pyqt5"
from traits.api import HasTraits, Button, Instance, Int, Bool
from traitsui.api import ModelView, View, Item, Label
from PyQt5.QtCore import pyqtRemoveInputHook

pyqtRemoveInputHook()  # enabled pdb.set_trace()


class App(HasTraits):
    """ Traits application model.
    """

    running = Bool(False)

    async def test_task(self):
        """ Test task that takes 1s to complete.
        """
        loop = asyncio.get_event_loop()
        self.running = True
        print("Running task.")
        await asyncio.sleep(1.0, loop)
        print("Task finished.")
        self.running = False


class AppView(ModelView):
    """ Traits application view.
    """

    model = Instance(App)

    test_task_btn = Button("Test Task")

    def close(self, info, is_ok):
        print("Close")
        return True

    def _test_task_btn_fired(self):
        print("Button pressed.")
        try:
            loop.create_task(self.model.test_task())
        except:
            traceback.print_exc()
            print("Problem")

    def default_traits_view(self):
        view = View(
            Label("Hello, I am a TraitsUI App using the QT event loop with Quamash."),
            Item("test_task_btn", show_label=False, enabled_when="not model.running"),
            resizable=True,
            title="Async TraitsUI Example",
        )
        return view


with loop:
    print("Launching app.")
    model = App()
    view = AppView(model=model)
    view.edit_traits()
    print("edit_traits")
    if sys.version_info[0] == 3 and sys.version_info[1] >= 8:
        asyncio.events._set_running_loop(loop)  # Need if using >= Python 3.8
    loop.run_forever()
    print("Finished run_forever()")
print("App closed.")