[issue2306] Update What's new in 3.0

[STINNER Victor]

STINNER Victor <victor.stinner at haypocalc.com> added the comment:

Copy/paste of the issue #4372:
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What's New in Python 3.0/Common stumbling blocks
has this "builtin.sorted() and list.sort() no longer accept the cmp
argument providing a comparison function. Use the key argument 
instead."

Please add "The __cmp__ special method is no longer used for
comparisons. Use __lt__ for sorting, __eq__ with __hash__, and other
rich comparisons as needed."

People are already stumbling on this.
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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue2306>
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