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

Lib/multiprocessing/managers.py

@@ -283,7 +283,7 @@ 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

@@ -248,6 +248,9 @@ Library
 - Issue #6766: Distributed reference counting added to multiprocessing
   to support nesting of shared values / proxy objects.
 
+- Issue #21201: Improves readability of multiprocessing error message.  Thanks
+  to Wojciech Walczak for patch.
+
 C API
 -----