Report a bug about switch_screen

[tsingwang]

from textual.app import App, ComposeResult
from textual.screen import Screen
from textual.widgets import Static, Header, Footer

class ScreenA(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Static("A")
        yield Footer()

class ScreenB(Screen):
    def compose(self) -> ComposeResult:
        yield Header()
        yield Static("B")
        yield Footer()

class ModalApp(App):
    SCREENS = {
        "a": ScreenA(),
        "b": ScreenB(),
    }

    BINDINGS = [
        ("1", "switch_screen('a')", "A"),
        ("2", "switch_screen('b')", "B"),
    ]

    def on_mount(self) -> None:
        self.push_screen("a")


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

This is sample code. When '21' pressed, it will crash. Log below:

╭──────────────────────────────────────────────────────────────────── Traceback (most recent call last) ─────────────────────────────────────────────────────────────────────╮
│ /home/tsing/.local/lib/python3.10/site-packages/textual/app.py:2488 in action_switch_screen                                                                                │
│                                                                                                                                                                            │
│   2485 │   │   Args:                                                                            ╭────────────────────────── locals ───────────────────────────╮            │
│   2486 │   │   │   screen: Name of the screen.                                                  │ screen = 'a'                                                │            │
│   2487 │   │   """                                                                              │   self = ModalApp(title='ModalApp', classes={'-dark-mode'}) │            │
│ ❱ 2488 │   │   self.switch_screen(screen)                                                       ╰─────────────────────────────────────────────────────────────╯            │
│   2489 │                                                                                                                                                                   │
│   2490 │   async def action_push_screen(self, screen: str) -> None:                                                                                                        │
│   2491 │   │   """An [action](/guide/actions) to push a new screen on to the stack and make it                                                                             │
│                                                                                                                                                                            │
│ /home/tsing/.local/lib/python3.10/site-packages/textual/app.py:1446 in switch_screen                                                                                       │
│                                                                                                                                                                            │
│   1443 │   │   │   )                                                                            ╭─────────────────────────────── locals ───────────────────────────────╮   │
│   1444 │   │   if self.screen is not screen:                                                    │ previous_screen = ScreenB(pseudo_classes={'enabled'})                │   │
│   1445 │   │   │   previous_screen = self._replace_screen(self._screen_stack.pop())             │          screen = 'a'                                                │   │
│ ❱ 1446 │   │   │   previous_screen._pop_result_callback()                                       │            self = ModalApp(title='ModalApp', classes={'-dark-mode'}) │   │
│   1447 │   │   │   next_screen, await_mount = self._get_screen(screen)                          ╰──────────────────────────────────────────────────────────────────────╯   │
│   1448 │   │   │   self._screen_stack.append(next_screen)                                                                                                                  │
│   1449 │   │   │   self.screen.post_message(events.ScreenResume())                                                                                                         │
│                                                                                                                                                                            │
│ /home/tsing/.local/lib/python3.10/site-packages/textual/screen.py:572 in _pop_result_callback                                                                              │
│                                                                                                                                                                            │
│   569 │                                                                                        ╭────────────────── locals ──────────────────╮                              │
│   570 │   def _pop_result_callback(self) -> None:                                              │ self = ScreenB(pseudo_classes={'enabled'}) │                              │
│   571 │   │   """Remove the latest result callback from the stack."""                          ╰────────────────────────────────────────────╯                              │
│ ❱ 572 │   │   self._result_callbacks.pop()                                                                                                                                 │
│   573 │                                                                                                                                                                    │
│   574 │   def _refresh_layout(                                                                                                                                             │
│   575 │   │   self, size: Size | None = None, full: bool = False, scroll: bool = False                                                                                     │
╰────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
IndexError: pop from empty list

The direct reason is _ push_ result_ callback not called when switch_screen, or check self._result_callbacks is empty when pop.

[github-actions]

Thank you for your issue. Give us a little time to review it.

PS. You might want to check the FAQ if you haven't done so already.

This is an automated reply, generated by FAQtory

[chitter99]

Same thing happened to me. I'm switching a screen that another screen has a callback on.

[rodrigogiraoserrao]

Thanks for opening this issue @tsingwang.

@chitter99 can you add a bit more context to your specific problem, please? Ideally with a minimal reproducible example?
It's likely that the issues are related but a code sample from you could be quite helpful.

[rodrigogiraoserrao]

Studying this a bit further revealed that there was another similar issue because switching to the currently active screen should be a no-op but it wasn't.

[github-actions]

Don't forget to star the repository!

Follow @textualizeio for Textual updates.

[mzebrak]

@rodrigogiraoserrao It looks like a similar issue still exists, but now for pop_screen. One of our users sent us:
(Textual version of 0.30.0)

/lib/python3.10/site-packages/textual/app.py:1732 in                                                                               │
│ pop_screen                                                                                                                       │
│                                                                                                                                  │
│   1729 │   │   │   │   "Can't pop screen; there must be at least one screen on the stack"                                        │
│   1730 │   │   │   )                                                                                                             │
│   1731 │   │   previous_screen = self._replace_screen(screen_stack.pop())                                                        │
│ ❱ 1732 │   │   previous_screen._pop_result_callback()                                                                            │
│   1733 │   │   self.screen._screen_resized(self.size)                                                                            │
│   1734 │   │   self.screen.post_message(events.ScreenResume())                                                                   │
│   1735 │   │   self.log.system(f"{self.screen} is active")                                                                       │
│                                                                                                                                  │
│                                                                                                                                  │
│/lib/python3.10/site-packages/textual/screen.py:635 in                                                                            │
│ _pop_result_callback                                                                                                             │
│                                                                                                                                  │
│   632 │                                                                                        ╭─── locals ────╮                 │
│   633 │   def _pop_result_callback(self) -> None:                                              │ self = Cart() │                 │
│   634 │   │   """Remove the latest result callback from the stack."""                          ╰───────────────╯                 │
│ ❱ 635 │   │   self._result_callbacks.pop()                                                                                       │
│   636 │                                                                                                                          │
│   637 │   def _refresh_layout(                                                                                                   │
│   638 │   │   self, size: Size | None = None, full: bool = False, scroll: bool = False                                           │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
IndexError: pop from empty list

[davep]

@mzebrak Do you think you could create a minimal isolated example of what your code is doing, such that it displays the issue? Would be an idea to create it as a fresh issue if this is something that's a bug in the current release; feel free to refer back to this one too.

[mzebrak]

@mzebrak Do you think you could create a minimal isolated example of what your code is doing, such that it displays the issue? Would be an idea to create it as a fresh issue if this is something that's a bug in the current release; feel free to refer back to this one too.

Unfortunately, I have no idea how to reproduce it, that's all I have. I suppose some sequence of several pop screens, switch screens and pop screens again

==== EDIT:

I've got it!
I think it's related to switch_screen call with screen as str and not Screen instance
My logging includes with screen as string postfix when push_screen or switch_screen is called with screen as str
Here's the sequence:

2023-07-31 12:43:03.893 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:03.895 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:04.438 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:05.852 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:08.068 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:09.302 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:11.912 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:13.077 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:14.283 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.301 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.315 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.330 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.341 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.350 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.353 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:14.422 | ⚠️ WARNING  | Textual issue with _pop_result_callback: switch_screen called with screen as string
2023-07-31 12:43:16.090 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:19.593 | ⚠️ WARNING  | Textual issue with _pop_result_callback: push_screen called 
2023-07-31 12:43:31.498 | ⚠️ WARNING  | Textual issue with _pop_result_callback: switch_screen called 
2023-07-31 12:43:34.968 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called
2023-07-31 12:43:35.002 | ⚠️ WARNING  | Textual issue with _pop_result_callback: pop_screen called

==== EDIT:

I've created a separate issue for this: #3041