Python exceptions can now be handled via QML

callCoro/callBackendCoro can now take onSuccess(result) and
onError(type, args, errorObject) callbacks.

src/python/app.py

@@ -61,9 +61,17 @@ class App:
 
 
     def _call_coro(self, coro: Coroutine, uuid: str) -> None:
-        self.run_in_loop(coro).add_done_callback(
-            lambda future: CoroutineDone(uuid=uuid, result=future.result()),
-        )
+        def on_done(future: Future) -> None:
+            try:
+                result    = future.result()
+                exception = None
+            except Exception as err:
+                result    = None
+                exception = err
+
+            CoroutineDone(uuid, result, exception)
+
+        self.run_in_loop(coro).add_done_callback(on_done)
 
 
     def call_backend_coro(self, name: str, uuid: str, args: Sequence[str] = (),

src/python/pyotherside_events.py

@@ -1,6 +1,6 @@
 from dataclasses import dataclass, field
 from enum import Enum
-from typing import Any, Dict, List, Union
+from typing import Any, Dict, List, Optional, Union
 
 import pyotherside
 
@@ -47,8 +47,9 @@ class AlertRequested(PyOtherSideEvent):
 class CoroutineDone(PyOtherSideEvent):
     """Indicate that an asyncio coroutine finished."""
 
-    uuid:   str = field()
-    result: Any = None
+    uuid:   str                    = field()
+    result: Any                    = None
+    exception: Optional[Exception] = None
 
 
 @dataclass