Another checkpoint -- some stuff I managed to do on the train.
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Guido van Rossum
parent
d74a1dc501
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3828768f45
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@ -129,25 +129,29 @@ Note:
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:func:`print` function calls, so this is mostly a non-issue for
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larger projects.
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Text Strings Vs. Bytes
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----------------------
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Text Vs. Data Instead Of Unicode Vs. 8-bit
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------------------------------------------
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Everything you thought you knew about binary data and Unicode has
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changed. There's a longer section below; here's a summary of the
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changes:
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changed:
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* Python 3.0 uses *strings* and *bytes* instead of *Unicode strings*
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and *8-bit strings*. The difference is that any attempt to mix
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strings and bytes in Python 3.0 raises a TypeError exception,
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whereas if you were to mix Unicode and 8-bit strings in Python 2.x,
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you would only get an exception if the 8-bit string contained
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non-ASCII values. As a consequence, pretty much all code that
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uses Unicode, encodings or binary data most likely has to change.
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The change is for the better, as in the 2.x world there were
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numerous bugs having to do with mixing encoded and unencoded text.
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XXX HIRO
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* You no longer need to use ``u"..."`` literals for Unicode text.
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However, you must use ``b"..."`` literals for binary data.
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* Python 3.0 uses the concepts of *text* and (binary) *data* instead
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of Unicode strings and 8-bit strings. All text is Unicode; however
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*encoded* Unicode is represented as binary data. The type used to
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hold text is :class:`str`, the type used to hold data is
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:class:`bytes`. The difference is that any attempt to mix text and
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data in Python 3.0 raises a TypeError exception, whereas if you were
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to mix Unicode and 8-bit strings in Python 2.x, you would only get
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an exception if the 8-bit string contained non-ASCII values. As a
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consequence, pretty much all code that uses Unicode, encodings or
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binary data most likely has to change. The change is for the
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better, as in the 2.x world there were numerous bugs having to do
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with mixing encoded and unencoded text.
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* You no longer use ``u"..."`` literals for Unicode text. However,
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you must use ``b"..."`` literals for binary data.
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* Files opened as text files (still the default mode for :func:`open`)
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always use an encoding to map between strings (in memory) and bytes
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@ -167,6 +171,50 @@ changes:
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don't have functionality enough in common to warrant a shared base
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class.
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* All backslashes in raw strings are interpreted literally. This
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means that ``'\U'`` and ``'\u'`` escapes in raw strings are not
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treated specially.
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XXX Deal with dupes below
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* There is only one text string type; its name is :class:`str` but its
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behavior and implementation are like :class:`unicode` in 2.x.
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* The :class:`basestring` superclass has been removed. The ``2to3``
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tool (see below) replaces every occurrence of :class:`basestring`
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with :class:`str`.
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* :pep:`3137`: There is a new type, :class:`bytes`, to represent
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binary data (and encoded text, which is treated as binary data until
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it is decoded). The :class:`str` and :class:`bytes` types cannot be
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mixed; you must always explicitly convert between them, using the
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:meth:`str.encode` (str -> bytes) or :meth:`bytes.decode` (bytes ->
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str) methods.
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* Like :class:`str`, the :class:`bytes` type is immutable. There is a
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separate *mutable* type to hold buffered binary data,
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:class:`bytearray`. Nearly all APIs that accept :class:`bytes` also
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accept :class:`bytearray`. The mutable API is based on
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:class:`collections.MutableSequence`.
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* :pep:`3138`: The :func:`repr` of a string no longer escapes
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non-ASCII characters. It still escapes control characters and code
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points with non-printable status in the Unicode standard, however.
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* :pep:`3120`: The default source encoding is now UTF-8.
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* :pep:`3131`: Non-ASCII letters are now allowed in identifiers.
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(However, the standard library remains ASCII-only with the exception
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of contributor names in comments.)
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* :pep:`3116`: New I/O implementation. The API is nearly 100%
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backwards compatible, but completely reimplemented (currently largely
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in Python). Also, binary files use bytes instead of strings.
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* The :mod:`StringIO` and :mod:`cStringIO` modules are gone. Instead,
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import :class:`io.StringIO` or :class:`io.BytesIO`, for text and
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data respectively.
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* See also the :ref:`unicode-howto`, which was updated for Python 3.0.
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Views And Iterators Instead Of Lists
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@ -254,8 +302,8 @@ Overview Of Syntax Changes
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This section gives a brief overview of every *syntactic* change in
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Python 3.0.
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Additions
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---------
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New Syntax
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----------
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* :pep:`3107`: Function argument and return value annotations. This
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provides a standardized way of annotating a function's parameters
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@ -304,8 +352,8 @@ Additions
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* Bytes literals are introduced with a leading ``b`` or ``B``.
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Changes
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-------
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Changed Syntax
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--------------
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* New :keyword:`raise` statement syntax: ``raise [expr [from expr]]``.
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Also note that string exceptions are no longer legal (:pep:`0352`).
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@ -333,8 +381,8 @@ Changes
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*must* now be spelled as ``...``. (Previously it could also be
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spelled as ``. . .``, by a mere accident of the grammar.)
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Removals
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--------
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Removed Syntax
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--------------
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* :pep:`3113`: Tuple parameter unpacking removed. You can no longer
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write ``def foo(a, (b, c)): ...``.
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@ -362,7 +410,6 @@ Removals
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(:pep:`0328`)
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Changes Already Present In Python 2.6
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=====================================
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@ -401,8 +448,7 @@ consulted for longer descriptions.
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* :ref:`pep-3112`. The ``b"..."`` string literal notation (and its
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variants like ``b'...'``, ``b"""..."""``, and ``br"..."``) now
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produces a literal of type :class:`bytes`. More about
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:class:`bytes` below.
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produces a literal of type :class:`bytes`.
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* :ref:`pep-3116`. The :mod:`io` module is now the standard way of
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doing file I/O, and the initial values of :data:`sys.stdin`,
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@ -411,14 +457,17 @@ consulted for longer descriptions.
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alias for :func:`io.open` and has additional keyword arguments
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*encoding*, *errors*, *newline* and *closefd*. Also note that an
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invalid *mode* argument now raises :exc:`ValueError`, not
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:exc:`IOError`.
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:exc:`IOError`. The binary file object underlying a text file
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object can be accessed as :attr:`f.buffer` (but beware that the
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text object maintains a buffer of itself in order to speed up
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the encoding and decoding operations).
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* :ref:`pep-3118`. The old builtin :func:`buffer` is now really gone;
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the new builtin :func:`memoryview` provides (mostly) similar
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functionality.
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* :ref:`pep-3119`. The :mod:`abc` module and the ABCs defined in the
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:mod:`collections` module plays a slightly more prominent role in
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:mod:`collections` module plays a somewhat more prominent role in
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the language now, and builtin collection types like :class:`dict`
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and :class:`list` conform to the :class:`collections.MutableMapping`
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and :class:`collections.MutableSequence` ABC, respectively.
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@ -427,11 +476,11 @@ consulted for longer descriptions.
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notation is the only one supported, and binary literals have been
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added.
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* :ref:`pep-3129`. This speaks for itself.
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* :ref:`pep-3129`.
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* :ref:`pep-3141`. The :mod:`numbers` module is another new use of
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ABCs, defining Python's "numeric tower". Also note the new
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:mod:`fractions` module.
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:mod:`fractions` module which implements :class:`numbers.Rational`.
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Library Changes
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@ -532,58 +581,14 @@ Some other library changes (not covered by :pep:`3108`):
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* Cleanup of the :mod:`random` module: removed the :func:`jumpahead` API.
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Strings And Bytes
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=================
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This section discusses the many changes in string XXX
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* There is only one string type; its name is :class:`str` but its behavior and
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implementation are like :class:`unicode` in 2.x.
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* The :class:`basestring` superclass has been removed. The ``2to3`` tool
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replaces every occurrence of :class:`basestring` with :class:`str`.
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* :pep:`3137`: There is a new type, :class:`bytes`, to represent
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binary data (and encoded text, which is treated as binary data until
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you decide to decode it). The :class:`str` and :class:`bytes` types
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cannot be mixed; you must always explicitly convert between them,
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using the :meth:`str.encode` (str -> bytes) or :meth:`bytes.decode`
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(bytes -> str) methods.
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.. XXX add bytearray
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* All backslashes in raw strings are interpreted literally. This means that
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``'\U'`` and ``'\u'`` escapes in raw strings are not treated specially.
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* :pep:`3138`: :func:`repr` of a string no longer escapes all
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non-ASCII characters. XXX
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* :pep:`3112`: Bytes literals, e.g. ``b"abc"``, create :class:`bytes`
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instances.
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* :pep:`3120`: UTF-8 default source encoding.
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* :pep:`3131`: Non-ASCII identifiers. (However, the standard library remains
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ASCII-only with the exception of contributor names in comments.)
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* :pep:`3116`: New I/O Implementation. The API is nearly 100% backwards
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compatible, but completely reimplemented (currently mostly in Python). Also,
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binary files use bytes instead of strings.
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* The :mod:`StringIO` and :mod:`cStringIO` modules are gone. Instead, import
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:class:`io.StringIO` or :class:`io.BytesIO`.
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:pep:`3101`: A New Approach To String Formatting
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================================================
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* A new system for built-in string formatting operations replaces the
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``%`` string formatting operator. (However, the ``%`` operator is
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still supported; it will be deprecated in Python 3.1 and removed
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from the language at some later time.)
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.. XXX expand this
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from the language at some later time.) Read :pep:`3101` for the full
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scoop.
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:pep:`3106`: Revamping dict :meth:`dict.keys`, :meth:`dict.items` and :meth:`dict.values`
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@ -632,16 +637,24 @@ Exception Stuff
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New Class And Metaclass Stuff
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=============================
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XXX Move to new syntax section???
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* Classic classes are gone.
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* :pep:`3115`: New Metaclass Syntax.
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* :pep:`3115`: New Metaclass Syntax. Instead of::
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* :pep:`3119`: Abstract Base Classes (ABCs); ``@abstractmethod`` and
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``@abstractproperty`` decorators; collection ABCs.
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class C:
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__metaclass__ = M
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...
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* :pep:`3129`: Class decorators.
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you now use::
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* :pep:`3141`: Numeric ABCs.
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class C(metaclass=M):
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...
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The module-global :data:`__metaclass__` variable is no longer supported.
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(It was a crutch to make it easier to default to new-style classes
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without deriving every class from :class:`object`.)
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Other Language Changes
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