mailpipe: use `messages.sort(...)`, not `m = sorted(m, ...)`.

diff --git a/pygrader/mailpipe.py b/pygrader/mailpipe.py
index daae3e281a53f1e49ba7e8cfc667d2714387a5bd..3f9f7c3d9bb69732ed1819a9157567bd03645c7b 100644 (file)
--- a/pygrader/mailpipe.py
+++ b/pygrader/mailpipe.py
@@ -662,7 +662,7 @@ def _load_messages(course, stream, mailbox=None, input_=None, output=None,
             ombox = _mailbox.Maildir(output, factory=None, create=True)
     else:
         raise ValueError(mailbox)
-    messages = sorted(messages, key=_get_message_time)
+    messages.sort(key=_get_message_time)
     for key,msg in messages:
         try:
             ret = _parse_message(