daemon error-handling: fix traceback.format_exception() on old python

The new API for traceback.format_exception was only added in python 3.10 (91e93794d5).

electrum/daemon.py

@@ -46,7 +46,7 @@ from .network import Network
 from .util import (json_decode, to_bytes, to_string, profiler, standardize_path, constant_time_compare, InvalidPassword)
 from .invoices import PR_PAID, PR_EXPIRED
 from .util import log_exceptions, ignore_exceptions, randrange, OldTaskGroup, UserFacingException, JsonRPCError
-from .util import EventListener, event_listener
+from .util import EventListener, event_listener, traceback_format_exception
 from .wallet import Wallet, Abstract_Wallet
 from .storage import WalletStorage
 from .wallet_db import WalletDB, WalletRequiresSplit, WalletRequiresUpgrade, WalletUnfinished
@@ -264,7 +264,7 @@ class AuthenticatedServer(Logger):
                 'message': "internal error while executing RPC",
                 'data': {
                     "exception": repr(e),
-                    "traceback": "".join(traceback.format_exception(e)),
+                    "traceback": "".join(traceback_format_exception(e)),
                 },
             }
         return web.json_response(response)

electrum/util.py

@@ -2064,6 +2064,14 @@ class nullcontext:
         pass
 
 
+def traceback_format_exception(exc: BaseException) -> Sequence[str]:
+    """Compatibility wrapper for stdlib traceback.format_exception using python 3.10+ API."""
+    if sys.version_info[:3] >= (3, 10):
+        return traceback.format_exception(exc)
+    else:
+        return traceback.format_exception(type(exc), value=exc, tb=exc.__traceback__)
+
+
 class classproperty(property):
     """~read-only class-level @property
     from https://stackoverflow.com/a/13624858 by denis-ryzhkov

tests/qt_util.py

@@ -6,6 +6,8 @@ from unittest import SkipTest
 
 from PyQt6.QtCore import QCoreApplication, QMetaObject, Qt, pyqtSlot, QObject
 
+from electrum.util import traceback_format_exception
+
 
 class TestQCoreApplication(QCoreApplication):
     @pyqtSlot()
@@ -76,7 +78,7 @@ def qt_test(func):
             if not res:
                 self._e = Exception('testcase timed out')
             if self._e:
-                print("".join(traceback.format_exception(self._e)))
+                print("".join(traceback_format_exception(self._e)))
                 # deallocate stored exception from qt thread otherwise we SEGV garbage collector
                 # instead, re-create using the exception message, special casing AssertionError and SkipTest
                 e = None