RuntimeError: There is no current event loop in thread 'asyncio_0'. happens on python 3.9

[Tim-Cao]

from textual import work
from textual.app import App, ComposeResult, events
from textual.containers import *
from textual.widgets import *


class ScriptApp(App):
    CSS = """
.unselected {
    display: none;
}

.unselected.visible {
    display: block;
}
"""

    def compose(self) -> ComposeResult:
        PROJECT_KEY = [
            ("LPS", "LPS"),
            ("LRQA", "LRQA"),
            ("LRAC", "LRAC"),
            ("COMMERCE", "COMMERCE"),
        ]

        yield Header()
        yield Label("Project Key:", id="project-key-label-2")
        yield Select(PROJECT_KEY, id="project-key-2")
        yield Label("Summary:", id="summary-label", classes="unselected")
        yield Input(id="summary", classes="unselected")
        yield Static()
        yield Button("Submit", id="button-7")
        yield Footer()

    @work(exclusive=True, thread=True)
    def create_issue(self) -> None:
        self.query_one("#button-7").disabled = True

        self.query_one("#summary").value = ""
        self.query_one("#project-key-2").clear()
        self.query_one("#button-7").disabled = False
        self.query_one("#summary").remove_class("visible")
        self.query_one("#summary-label").remove_class("visible")

    def on_button_pressed(self, event: Button.Pressed) -> None:
        if event.button.id == "button-7":
            self.create_issue()

    def on_select_changed(self, event: Select.Changed) -> None:
        self.query_one("#summary").set_class(event.value != Select.BLANK, "visible")
        self.query_one("#summary-label").set_class(
            event.value != Select.BLANK, "visible"
        )


app = ScriptApp()

if __name__ == "__main__":
    app.run()

[willmcgugan]

Threaded workers need a little more care. You won't be able to update the DOM directly, but you can send messages or use App.call_from_thread.

See this section in the docs for details... https://textual.textualize.io/guide/workers/#thread-workers

[Tim-Cao]

Thanks for your help! It works.

    @work(exclusive=True, thread=True)
    def create_issue(self) -> None:
        self.query_one("#button-7").disabled = True

        self.query_one("#summary").value = ""
        self.query_one("#project-key-2").clear()
        self.query_one("#button-7").disabled = False
        self.call_from_thread(self.query_one("#summary").remove_class, "visible")
        self.call_from_thread(self.query_one("#summary-label").remove_class, "visible")