There was a confusion in my checkin of the code to support list() with

gvanrossum · gvanrossum · commit 8d5bef7fb88d · 1998-09-14T17:36:51.000Z
and without a message number argument: the argument was called 'msg'
but the code expected it to be called 'which'.  In line with the other
methods, I've renamed the argument to 'which', and adapted the doc
string not to refer to 'msg'.
diff --git a/Lib/poplib.py b/Lib/poplib.py
@@ -196,14 +196,14 @@ def stat(self):
 		return (numMessages, sizeMessages)
 
 
-	def list(self, msg=None):
+	def list(self, which=None):
 		"""Request listing, return result.
 
-		Result without a msg argument is in form
+		Result without a message number argument is in form
 		['response', ['mesg_num octets', ...]].
 
-		Result when a msg argument is given is a single response:
-		the "scan listing" for that message.
+		Result when a message number argument is given is a
+		single response: the "scan listing" for that message.
 		"""
 		if which:
 			return self._shortcmd('LIST %s' % which)
