Adopt ExceptionGroup handling without an external library (#894)

* Adopt ExceptionGroup handling without an external library

* Python <3.11 behaviour not changed

Fix: #893

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

test_requirements.txt

@@ -2,8 +2,8 @@ tornado>=5
 twisted
 trio
 zmq
-exceptiongroups
+exceptiongroups;python_version<'3.11'
 windows-curses;sys_platform=="win32"
 pyserial
 # for test run
-coverage[toml]
+coverage[toml]

urwid/event_loop/trio_loop.py

@@ -26,13 +26,16 @@
 from __future__ import annotations
 
 import logging
+import sys
 import typing
 
-import exceptiongroup
 import trio
 
 from .abstract_loop import EventLoop, ExitMainLoop
 
+if sys.version_info < (3, 11):
+    from exceptiongroup import BaseExceptionGroup  # pylint: disable=redefined-builtin  # backport
+
 if typing.TYPE_CHECKING:
     import io
     from collections.abc import Awaitable, Callable, Hashable, Mapping
@@ -156,8 +159,10 @@ def run(self) -> None:
 
         emulate_idle_callbacks = _TrioIdleCallbackInstrument(self._idle_callbacks)
 
-        with exceptiongroup.catch({BaseException: self._handle_main_loop_exception}):
+        try:
             trio.run(self._main_task, instruments=[emulate_idle_callbacks])
+        except BaseException as exc:
+            self._handle_main_loop_exception(exc)
 
     async def run_async(self) -> None:
         """Starts the main loop and blocks asynchronously until the main loop exits.
@@ -179,12 +184,14 @@ async def run_async(self) -> None:
 
         emulate_idle_callbacks = _TrioIdleCallbackInstrument(self._idle_callbacks)
 
-        with exceptiongroup.catch({BaseException: self._handle_main_loop_exception}):
+        try:
             trio.lowlevel.add_instrument(emulate_idle_callbacks)
             try:
                 await self._main_task()
             finally:
                 trio.lowlevel.remove_instrument(emulate_idle_callbacks)
+        except BaseException as exc:
+            self._handle_main_loop_exception(exc)
 
     def watch_file(
         self,
@@ -225,12 +232,11 @@ def _handle_main_loop_exception(self, exc: BaseException) -> None:
         """Handles exceptions raised from the main loop, catching ExitMainLoop
         instead of letting it propagate through.
 
-        Note that since Trio may collect multiple exceptions from tasks into a
-        Trio MultiError, we cannot simply use a try..catch clause, we need a
-        helper function like this.
+        Note that since Trio may collect multiple exceptions from tasks into an ExceptionGroup,
+        we cannot simply use a try..catch clause, we need a helper function like this.
         """
         self._idle_callbacks.clear()
-        if isinstance(exc, exceptiongroup.BaseExceptionGroup) and len(exc.exceptions) == 1:
+        if isinstance(exc, BaseExceptionGroup) and len(exc.exceptions) == 1:
             exc = exc.exceptions[0]
 
         if isinstance(exc, ExitMainLoop):