bpo-5001: More-informative multiprocessing error messages (#3079)

* Make error message more informative

Replace assertions in error-reporting code with more-informative version that doesn't cause confusion over where and what the error is.

* Additional clarification + get travis to check

* Change from SystemError to TypeError

As suggested in PR comment by @pitrou, changing from SystemError; TypeError appears appropriate.

* NEWS file installation; ACKS addition (will do my best to justify it by additional work)

* Making current AssertionErrors in multiprocessing more informative

* Blurb added re multiprocessing managers.py, queues.py cleanup

* Further multiprocessing cleanup - went through pool.py

* Fix two asserts in multiprocessing/util.py

* Most asserts in multiprocessing more informative

* Didn't save right version

* Further work on multiprocessing error messages

* Correct typo

* Correct typo v2

* Blasted colon... serves me right for trying to work on two things at once

* Simplify NEWS entry

* Update 2017-08-18-17-16-38.bpo-5001.gwnthq.rst

* Update 2017-08-18-17-16-38.bpo-5001.gwnthq.rst

OK, never mind.

* Corrected (thanks to pitrou) error messages for notify

* Remove extraneous backslash in docstring.

1 files changed, 6 insertions, 2 deletions

diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
index ba9b17c..7a621a5 100644
--- a/Lib/multiprocessing/connection.py
+++ b/Lib/multiprocessing/connection.py
@@ -720,7 +720,9 @@ FAILURE = b'#FAILURE#'
 
 def deliver_challenge(connection, authkey):
     import hmac
-    assert isinstance(authkey, bytes)
+    if not isinstance(authkey, bytes):
+        raise ValueError(
+            "Authkey must be bytes, not {0!s}".format(type(authkey)))
     message = os.urandom(MESSAGE_LENGTH)
     connection.send_bytes(CHALLENGE + message)
     digest = hmac.new(authkey, message, 'md5').digest()
@@ -733,7 +735,9 @@ def deliver_challenge(connection, authkey):
 
 def answer_challenge(connection, authkey):
     import hmac
-    assert isinstance(authkey, bytes)
+    if not isinstance(authkey, bytes):
+        raise ValueError(
+            "Authkey must be bytes, not {0!s}".format(type(authkey)))
     message = connection.recv_bytes(256)         # reject large message
     assert message[:len(CHALLENGE)] == CHALLENGE, 'message = %r' % message
     message = message[len(CHALLENGE):]