Bluetooth off throws an unhandleable error on Mac

[felixbade]

• bleak version: 0.19.5
• Python version: 3.10.9 (via Homebrew)
• Operating System: macOS 12.6 (M1 arm64)

Description

Running the scanner when device Bluetooth is turned off throws an exception that is not possible to catch (unraisable?).

I was expecting the error to be catchable so I can show a more friendly error to the user that they need to turn their Bluetooth on.

What I Did

Running this code with Bluetooth turned off.

import asyncio
from bleak import BleakScanner
from bleak.exc import BleakError

async def callback(device, adv_data):
    pass

async def main():
    try:
        scanner = BleakScanner(callback, service_uuids=[])
    except BleakError as error:
        print('Error:', error)

asyncio.run(main())

Expected output:

Error: Bluetooth device is turned off

Actual output:

Error: Bluetooth device is turned off
Exception ignored in: <CentralManagerDelegate objective-c instance 0x0>
Traceback (most recent call last):
  File "/opt/homebrew/lib/python3.10/site-packages/bleak/backends/corebluetooth/CentralManagerDelegate.py", line 103, in __del__
    self.central_manager.removeObserver_forKeyPath_(self, "isScanning")
IndexError: NSRangeException - Cannot remove an observer <CentralManagerDelegate 0x14bed5b70> for the key path "isScanning" from <CBCentralManager 0x600002dfc580> because it is not registered as an observer.
Exception ignored in: <function CentralManagerDelegate.__del__ at 0x10405fac0>

Logs

2023-02-13 22:08:43,494 bleak.backends.corebluetooth.CentralManagerDelegate DEBUG: centralManagerDidUpdateState_
2023-02-13 22:08:43,495 bleak.backends.corebluetooth.CentralManagerDelegate DEBUG: Bluetooth powered off
Error: Bluetooth device is turned off
Exception ignored in: <CentralManagerDelegate objective-c instance 0x0>
Traceback (most recent call last):
  File "/opt/homebrew/lib/python3.10/site-packages/bleak/backends/corebluetooth/CentralManagerDelegate.py", line 103, in __del__
    self.central_manager.removeObserver_forKeyPath_(self, "isScanning")
IndexError: NSRangeException - Cannot remove an observer <CentralManagerDelegate 0x149ec3510> for the key path "isScanning" from <CBCentralManager 0x600000950600> because it is not registered as an observer.
Exception ignored in: <function CentralManagerDelegate.__del__ at 0x103d83ac0>

Extra

Ignoring unraisable errors makes the situation a bit better, but not perfect, and also this feels like a very dirty solution:

import asyncio
from bleak import BleakScanner
from bleak.exc import BleakError

async def callback(device, adv_data):
    pass

async def main():
    try:
        scanner = BleakScanner(callback, service_uuids=[])
    except BleakError as error:
        import sys
        sys.unraisablehook = lambda x: None

        print('Error:', error)

asyncio.run(main())

Output:

Error: Bluetooth device is turned off
Exception ignored in: <function CentralManagerDelegate.__del__ at 0x1040cfb50>