Error raised when an app is terminated with an empty SelectionList.

[YooSunYoung]

Hi!

I was writing a simple tool to add/delete kafka topics with textual.
Whenever I exit the app after deleting all Selection options in the SelectionList, it raised OptionDoesNotExist error that I don't understand...

Can you please help me...?

Error Message

Full Error Message

Traceback (most recent call last): File ".tox/dev/lib/python3.10/site-packages/textual/message_pump.py", line 536, in _process_messages_loop await self._dispatch_message(message) File ".tox/dev/lib/python3.10/site-packages/textual/message_pump.py", line 599, in _dispatch_message await self._on_message(message) File ".tox/dev/lib/python3.10/site-packages/textual/message_pump.py", line 687, in _on_message await invoke(method, message) File ".tox/dev/lib/python3.10/site-packages/textual/_callback.py", line 74, in invoke return await _invoke(callback, *params) File ".tox/dev/lib/python3.10/site-packages/textual/_callback.py", line 34, in _invoke result = callback(*params[:parameter_count]) File ".tox/dev/lib/python3.10/site-packages/textual/widgets/_selection_list.py", line 579, in _on_option_list_option_highlighted self.post_message(self.SelectionHighlighted(self, event.option_index)) File ".tox/dev/lib/python3.10/site-packages/textual/widgets/_selection_list.py", line 172, in __init__ ] = selection_list.get_option_at_index(index) File ".tox/dev/lib/python3.10/site-packages/textual/widgets/_selection_list.py", line 603, in get_option_at_index return cast("Selection[SelectionType]", super().get_option_at_index(index)) File "/.tox/dev/lib/python3.10/site-packages/textual/widgets/_option_list.py", line 836, in get_option_at_index raise OptionDoesNotExist( textual.widgets._option_list.OptionDoesNotExist: There is no option with an index of 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "~/anaconda3/envs/benchmark/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "~/anaconda3/envs/benchmark/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "./tests/executables/empty_selection_list_error.py", line 162, in <module>
    app.run()
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 1400, in run
    asyncio.run(run_app())
  File "~/anaconda3/envs/benchmark/lib/python3.10/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "~/anaconda3/envs/benchmark/lib/python3.10/asyncio/base_events.py", line 649, in run_until_complete
    return future.result()
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 1389, in run_app
    await self.run_async(
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 1361, in run_async
    await app._shutdown()
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 2424, in _shutdown
    await self._close_all()
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 2416, in _close_all
    await child._close_messages()
  File ".tox/dev/lib/python3.10/site-packages/textual/message_pump.py", line 462, in _close_messages
    await self._task
  File ".tox/dev/lib/python3.10/site-packages/textual/message_pump.py", line 481, in _process_messages
    await self._process_messages_loop()
  File ".tox/dev/lib/python3.10/site-packages/textual/message_pump.py", line 541, in _process_messages_loop
    self.app._handle_exception(error)
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 2064, in _handle_exception
    self._fatal_error()
  File ".tox/dev/lib/python3.10/site-packages/textual/app.py", line 2069, in _fatal_error
    traceback = Traceback(
  File ".tox/dev/lib/python3.10/site-packages/rich/traceback.py", line 264, in __init__
    trace = self.extract(
  File ".tox/dev/lib/python3.10/site-packages/rich/traceback.py", line 449, in extract
    locals={
  File ".tox/dev/lib/python3.10/site-packages/rich/traceback.py", line 450, in <dictcomp>
    key: pretty.traverse(
  File ".tox/dev/lib/python3.10/site-packages/rich/pretty.py", line 853, in traverse
    node = _traverse(_object, root=True)
  File ".tox/dev/lib/python3.10/site-packages/rich/pretty.py", line 648, in _traverse
    args = list(iter_rich_args(rich_repr_result))
  File ".tox/dev/lib/python3.10/site-packages/rich/pretty.py", line 615, in iter_rich_args
    for arg in rich_args:
  File ".tox/dev/lib/python3.10/site-packages/textual/widgets/_selection_list.py", line 189, in __rich_repr__
    yield "selection", self.selection
AttributeError: 'SelectionHighlighted' object has no attribute 'selection'

Reproduce Error

• python version: 3.10
• textual version: 0.40.0

Here is the code snippet of very simplified app that can reproduce the error:

empty_selection_list_error.py

from textual.app import App, ComposeResult, Screen
from textual.containers import Container, Horizontal, VerticalScroll
from textual.widgets import Button, Header, Pretty, SelectionList, Static
from textual.widgets.selection_list import Selection

class FakeServer:
    def __init__(self) -> None:
        self._options = dict()
    
    @property
    def options(self) -> dict:
        return self._options

    def populate_option(self):
        import uuid
        new_opt = uuid.uuid4().hex
        self._options.setdefault(new_opt, new_opt)
    
    def remove_option(self, opt_name) -> None:
        self._options.pop(opt_name, None)
    
    def remove_options(self, opt_names: list) -> None:
        for opt_name in opt_names:
            self.remove_option(opt_name)


class OptionControlButtons(Horizontal):
    def compose(self) -> ComposeResult:
        yield Button('Add Option ➕', id='add-option')
        yield Button("Refresh ↻", id='refresh')
        yield Button("Select All ✅ ", id='all')
        yield Button("Delete Selected 🗑️ ", id='delete')
        yield Button("↵ Back to log in", id='back-to-login')
        yield Button("Exit ❌", id='exit')


class WarningScreen(Screen):
    def __init__(self, *instructions: Static | Pretty, **option_callbacks) -> None:
        super().__init__()
        self.instructions = instructions
        self.option_callbacks = option_callbacks

    def compose(self) -> ComposeResult:
        with VerticalScroll():
            for instruction in self.instructions:
                yield instruction
        with Horizontal():
            for option_callback in self.option_callbacks:
                yield Button(option_callback, id=option_callback)

    def on_button_pressed(self, event: Button.Pressed):
        event.stop()

        if (b_id := event.button.id) is not None and (
            callback := self.option_callbacks.get(b_id)
        ) is not None:
            callback()

        self.app.pop_screen()


class SampleScreen(Screen):
    DEFAULT_CSS = """
    OptionControlButtons {
        height: auto;
        padding: 1;
    }

    VerticalScroll {
        padding: 1;
        height: auto;
    }

    SelectionList {
        padding: 1;
        border: solid $accent;
    }
    """

    def __init__(self) -> None:
        super().__init__(name="Sample Screen", id=None)
        self.server = FakeServer()
        self.options = SelectionList()
        self.options.border_title = f"Options"

    def on_mount(self) -> None:
        self.refresh_options()

    def refresh_options(self) -> None:
        all_options = self.server.options
        existing_options = [option for option in self.options._option_ids]
        
        removed = [option for option in existing_options if option not in all_options]
        for removed_option in removed:
            self.options.remove_option(removed_option)
        
        new_options = [option for option in all_options if option not in existing_options]
        for new_option in new_options:
            self.options.add_option(Selection(new_option, new_option, False, id=new_option))

    def delete_selected(self):
        if selected := self.options.selected:
            def yes_callback():
                self.server.remove_options(selected)
                self.refresh_options()
            self.app.push_screen(
                WarningScreen(
                    Static("Following options will be deleted."),
                    Pretty(selected),
                    Static("Continue?"),
                    yes=yes_callback,
                    no=lambda: None,
                )
            )

    def compose(self) -> ComposeResult:
        yield Header(show_clock=True)
        yield OptionControlButtons()
        with VerticalScroll():
            yield self.options

    def on_button_pressed(self, event: Button.Pressed):
        if event.button.id == "add-option":
            self.server.populate_option()
            event.stop()
            self.refresh_options()
        elif event.button.id == "delete":
            self.delete_selected()
            event.stop()
        elif event.button.id == 'refresh':
            self.refresh_options()
            event.stop()
        elif event.button.id == 'all':
            self.options.select_all()
            event.stop()

class SampleLoginScreen(Screen):
    def compose(self) -> ComposeResult:
        yield Container(Button("LOG IN"))

    def on_button_pressed(self, _: Button.Pressed):
        self.app.push_screen(SampleScreen())


class Sample(App):
    def on_mount(self) -> None:
        self.title = "Sample App"
        self.push_screen(SampleLoginScreen())

    def on_button_pressed(self, event: Button.Pressed) -> None:
        event.stop()
        if event.button.id == 'exit':
            self.exit()
        elif event.button.id == 'back-to-login':
            self.pop_screen()

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

Here is the demo of the error with the code above:

[davep]

This isn't an answer to the question, and that's quite a bit of code to wade through to be able to help (although it seems clear whatever is going on is happening around SampleScreen.refresh_options) so you might want to think about working on a MRE to help narrow this down, but an observation I wanted to make was about this line of code:

existing_options = [option for option in self.options._option_ids]

_option_ids is a Textual internal (as is signified by the leading underscore). If you write code that relies on internals there's a very good chance it could stop working at some point in the future; either because the form of the data in that internal changes, or because it simply goes away.

[davep]

You were doing a far better job than I was, 'cos I totally confused myself.

PS: I think the bug might be in SelectionList._on_option_list_option_highlighted; at least it might point to the cause. If I add a check that self.highlighted is not None it removes the issue:

        event.stop()
        if self.highlighted is not None:
            self.post_message(self.SelectionHighlighted(self, event.option_index))

If that isn't the fix, I suspect that points to the underlying cause (but I suspect this is the thing to be doing).

[TomJGooding]

Right, that's what was confusing me since this shouldn't be None based on when OptionHighlighted is posted. Especially when nothing is actually highlighted in the example above!

[davep]

Yeah, that bit is very curious.

[TomJGooding]

While checking back on my outstanding issues, I found #3560 which I raised off the back off this discussion. I think this problem is resolved in the latest version of Textual, though I confess my memory is a bit hazy on the specifics!

[YooSunYoung]

Thank you!
I also tried again and it worked as you said so I could update my tool in our package : D

[TomJGooding]

I suspect the problem is that your FakeServer updates and Textual interface are getting out of sync - perhaps the Worker API would help here.

[YooSunYoung]

Thank you for the advice, it is indeed what we needed, but the error still occurs even though I don't use the FakeServer...
I posted a shorter example in another thread: #3559 (reply in thread)

[YooSunYoung]

I am currently using a workaround to replace SelectionList with a new SelectionList instance when it's refreshed.

This seems like to solve the problem but I am not sure if it is a good practice to destroy and create a widget instance so frequently....