Issue #21201: Improves readability of multiprocessing error message from server to client for certain exceptions

Lib/multiprocessing/managers.py

@@ -275,7 +275,7 @@ class Server(object):
                 try:
                     send(msg)
                 except Exception as e:
-                    send(('#UNSERIALIZABLE', repr(msg)))
+                    send(('#UNSERIALIZABLE', format_exc()))
             except Exception as e:
                 util.info('exception in thread serving %r',
                         threading.current_thread().name)

Misc/NEWS

@@ -221,6 +221,9 @@ Library
 - Issue #27930: Improved behaviour of logging.handlers.QueueListener.
   Thanks to Paulo Andrade and Petr Viktorin for the analysis and patch.
 
+- Issue #21201: Improves readability of multiprocessing error message.  Thanks
+  to Wojciech Walczak for patch.
+
 IDLE
 ----