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Complete What's New in 3.3 about PEP 393

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Victor Stinner 2011-09-29 02:56:16 +02:00
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@ -65,6 +65,28 @@ XXX Add list of changes introduced by :pep:`393` here:
either ``0xFFFF`` or ``0x10FFFF`` for backward compatibility, and it should
not be used with the new Unicode API (see :issue:`13054`).
* Non-BMP characters (U+10000-U+10FFFF range) are no more special cases.
``'\U0010FFFF'[0]`` is now ``'\U0010FFFF'`` on any platform, instead of
``'\uDFFF'`` on narrow build or ``'\U0010FFFF'`` on wide build. And
``len('\U0010FFFF')`` is now ``1`` on any platform, instead of ``2`` on
narrow build or ``1`` on wide build. More generally, most bugs related to
non-BMP characters are now fixed. For example, :func:`unicodedata.normalize`
handles correctly non-BMP characters on all platforms.
* The storage of Unicode string is now adapted on the content of the string.
Pure ASCII and Latin1 strings (U+0000-U+00FF) use 1 byte per character, BMP
strings (U+0000-U+FFFF) use 2 bytes per character, and non-BMP characters
(U+10000-U+10FFFF range) use 4 bytes per characters. The memory usage of
Python 3.3 is two to three times smaller than Python 3.2, and a little bit
better than Python 2.7, on a `Django benchmark
<http://mail.python.org/pipermail/python-dev/2011-September/113714.html>`_.
* The PEP 393 is fully backward compatible. The legacy API should remain
available at least five years. Applications using the legacy API will not
fully benefit of the memory reduction, or worse may use a little bit more
memory, because Python may have to maintain two versions of each string (in
the legacy format and in the new efficient storage).
Other Language Changes
======================
@ -334,3 +356,9 @@ that may require changes to your code:
.. Issue #10998: -Q command-line flags are related artifacts have been
removed. Code checking sys.flags.division_warning will need updating.
Contributed by Éric Araujo.
* :pep:`393`: The :c:type:`Py_UNICODE` type and all functions using this type
are deprecated. To fully benefit of the memory footprint reduction provided
by the PEP 393, you have to convert your code to the new Unicode API. Read
the porting guide: XXX.