Cannot register custom exception handler

[lgedgar]

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Describe the bug

I need to register a "catch-all" exception handler, to help identify bugs in development. Some errors may possibly arise from Flet controls but more often they will be result of backend API calls failing etc.

I previously did this via sys.excepthook and it did the trick fine, but this was under Flet 0.19.0 and it appears this approach no longer works with Flet 0.21.2+

I then turned to setting Page.on_error but this either does not work, or at least does not do what I was hoping.

I of course prefer to use latest Flet but currently this feels less "safe" given I have no insight to new errors.

Code sample

Logs

# -*- coding: utf-8; -*-

import sys
import threading

import flet as ft


def sample_main(page):

    def handle_error(exc_type, exc_value, exc_traceback):
        print("\n\nGOT UNHANDLED ERROR\n\n")

    def sys_exc_hook(exc_type, exc_value, exc_traceback):
        handle_error(exc_type, exc_value, exc_traceback)
        sys.__excepthook__(exc_type, exc_value, exc_traceback)

    sys.excepthook = sys_exc_hook

    # custom exception hook for threads (requires python 3.8)
    # cf. https://docs.python.org/3/library/threading.html#threading.excepthook
    v = sys.version_info
    if v.major >= 3 and v.minor >= 8:

        def thread_exc_hook(args):
            handle_error(args.exc_type, args.exc_value, args.exc_traceback)
            # nb. as of python 3.10 could just call threading.__excepthook__ instead
            # cf. https://docs.python.org/3/library/threading.html#threading.__excepthook__
            orig_thread_hook(args)

        # nb. as of python 3.10 the original hook is accessible, we needn't save the ref
        # cf. https://docs.python.org/3/library/threading.html#threading.__excepthook__
        orig_thread_hook = threading.excepthook

        threading.excepthook = thread_exc_hook

    def page_error(e):
        print('\n\nGOT PAGE ERROR:', e, '\n')

    page.on_error = page_error

    def on_click(e):
        print('GOT BUTTON CLICK', e)
        raise RuntimeError("whoops")

    page.add(ft.ElevatedButton("click me", on_click=on_click))


def run_sample_app():
    ft.app(target=sample_main)


if __name__ == '__main__':
    run_sample_app()

To reproduce

Running the code above with Flet 0.19.0 does print "GOT UNHANDLED ERROR" when clicking the button. But running it with newer Flet, the button click error still raises and a traceback is printed to console, but no "GOT UNHANDLED ERROR" message and so my custom hook is being ignored somehow.

I did try registering just the sys hook and then just the threading hook, to see which was actually getting called under Flet 0.19.0 and it seems the threading hook was being called, not the sys hook. But again neither gets called with newer Flet.

I then added the Page.on_error snippet in the hopes it would get called, but it also is not getting called - this is true with both the older and newer Flet.

Expected behavior

I need a reliable way to detect unhandled errors, so I can "handle" them in a minimal way. Details of the error will be logged but also sent via email, and I need to show a brief message to the user indicating that an error was encountered. All of this did work with Flet 0.19.0 and a custom excepthook but now I'm not sure how to register a handler that actually works?

Docs for Page.on_error makes me think this is what I should perhaps be using instead of hacking global excepthook, but #431 makes me think this was always meant as a more "Flet-specific" error handler and perhaps not what I would want?

I also looked over https://docs.flutter.dev/testing/errors but do not yet understand enough about the Flutter side to fully grok what this means for me in Flet-land.

Screenshots / Videos

Screenshots / Video demonstration

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Operating System

Linux

Operating system details

Debian 12

Flet version

0.23.2

Regression

Yes, it used to work in a previous Flet version (please specify the version in additional details)

Suggestions

I'm not 100% sure that my desired approach is the correct one; for instance Page.on_error seems promising instead of the excepthook overrides. And/or maybe a global error handler is not the best way to solve this in the first place? But it has worked okay in the past with other (non-Flet) projects..

Ideally:

• i discover how to correctly register "global" error handler
• possibly, Flet docs are updated accordingly
• possibly, Flet code must change to accommodate (e.g. Page.on_error improved) ?

Logs

Logs

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Additional details

Global threading excepthook used to work under Flet 0.19.0

Also - the above is all using Python 3.11.2

[nickstuer]

I know this is old but in case someone else comes across this, here is a work around:

import pprint
import os
import traceback

def exception_handler(loop, context):
  print("error")
  pprint.pprint(context['exception'])
  logger.info(f"{context['exception']}: {''.join(traceback.format_tb(context['exception'].__traceback__))}")
  self.page.window_destroy()

async def sample_main(page: ft.Page):
  loop = asyncio.get_running_loop()
  loop.set_exception_handler(exception_handler)```

Must add async keyword.