gh-158497: Keep the worker traceback in ProcessPoolExecutor.map()

Lib/concurrent/futures/process.py

@@ -207,7 +207,7 @@ def _process_chunk(fn, chunk):
         try:
             result = (fn(*args), None)
         except BaseException as exc:
-            result = (None, exc)
+            result = (None, _ExceptionWithTraceback(exc, exc.__traceback__))
         results.append(result)
     return results
 

Lib/test/test_concurrent_futures/test_process_pool.py

@@ -14,7 +14,7 @@
 from test.support import hashlib_helper, threading_helper, warnings_helper
 from test.test_importlib.metadata.fixtures import parameterize
 
-from .executor import ExecutorTest, mul
+from .executor import ExecutorTest, mul, raiser
 from .util import (
     ProcessPoolForkMixin, ProcessPoolForkserverMixin, ProcessPoolSpawnMixin,
     create_executor_tests, setup_module)
@@ -141,6 +141,16 @@ def test_traceback(self):
         self.assertIn('raise RuntimeError(123) # some comment',
                       f1.getvalue())
 
+    @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
+    def test_map_traceback(self):
+        # The traceback from the child process is also kept for map().
+        i = self.executor.map(raiser, [RuntimeError])
+        with self.assertRaises(RuntimeError) as cm:
+            next(i)
+        cause = cm.exception.__cause__
+        self.assertIs(type(cause), futures.process._RemoteTraceback)
+        self.assertIn('raise exception(msg)', cause.tb)
+
     def test_traceback_when_child_process_terminates_abruptly(self):
         # gh-139462 enhancement - BrokenProcessPool exceptions
         # should describe which process terminated.

Misc/NEWS.d/next/Library/2026-11-03-17-53-17.gh-issue-158497.gqFmXJ.rst

@@ -0,0 +1,3 @@
+Fix :meth:`Executor.map() <concurrent.futures.Executor.map>` of a
+:class:`~concurrent.futures.ProcessPoolExecutor` losing the traceback of an
+exception raised in a worker process.