2011/12/12 Victor Stinner <victor.stinner@haypocalc.com>
"When sorting a list using the sort() method, attempting to inspect or mutate the content of the list will result in undefined behaviour."

But is this even true? in listobject.c::listsort(), since 2002,
/* The list is temporarily made empty, so that mutations performed
 * by comparison functions can't affect the slice of memory we're
 * sorting (allowing mutations during sorting is a core-dump
 * factory, since ob_item may change).
 */
So behaviour is not undefined at all... maybe this report is only based on note #10 of the documentation:
http://docs.python.org/library/stdtypes.html#mutable-sequence-types
and only considers python 2.2 or older...

--
Amaury Forgeot d'Arc