[Python-3000-checkins] r67488 - python/branches/py3k/Doc/whatsnew/3.0.rst
guido.van.rossum
python-3000-checkins at python.org
Wed Dec 3 03:03:20 CET 2008
Author: guido.van.rossum
Date: Wed Dec 3 03:03:19 2008
New Revision: 67488
Log:
Another checkpoint -- some stuff I managed to do on the train.
Modified:
python/branches/py3k/Doc/whatsnew/3.0.rst
Modified: python/branches/py3k/Doc/whatsnew/3.0.rst
==============================================================================
--- python/branches/py3k/Doc/whatsnew/3.0.rst (original)
+++ python/branches/py3k/Doc/whatsnew/3.0.rst Wed Dec 3 03:03:19 2008
@@ -129,25 +129,29 @@
:func:`print` function calls, so this is mostly a non-issue for
larger projects.
-Text Strings Vs. Bytes
-----------------------
+Text Vs. Data Instead Of Unicode Vs. 8-bit
+------------------------------------------
Everything you thought you knew about binary data and Unicode has
-changed. There's a longer section below; here's a summary of the
-changes:
+changed:
-* Python 3.0 uses *strings* and *bytes* instead of *Unicode strings*
- and *8-bit strings*. The difference is that any attempt to mix
- strings and bytes in Python 3.0 raises a TypeError exception,
- whereas if you were to mix Unicode and 8-bit strings in Python 2.x,
- you would only get an exception if the 8-bit string contained
- non-ASCII values. As a consequence, pretty much all code that
- uses Unicode, encodings or binary data most likely has to change.
- The change is for the better, as in the 2.x world there were
- numerous bugs having to do with mixing encoded and unencoded text.
+XXX HIRO
-* You no longer need to use ``u"..."`` literals for Unicode text.
- However, you must use ``b"..."`` literals for binary data.
+* Python 3.0 uses the concepts of *text* and (binary) *data* instead
+ of Unicode strings and 8-bit strings. All text is Unicode; however
+ *encoded* Unicode is represented as binary data. The type used to
+ hold text is :class:`str`, the type used to hold data is
+ :class:`bytes`. The difference is that any attempt to mix text and
+ data in Python 3.0 raises a TypeError exception, whereas if you were
+ to mix Unicode and 8-bit strings in Python 2.x, you would only get
+ an exception if the 8-bit string contained non-ASCII values. As a
+ consequence, pretty much all code that uses Unicode, encodings or
+ binary data most likely has to change. The change is for the
+ better, as in the 2.x world there were numerous bugs having to do
+ with mixing encoded and unencoded text.
+
+* You no longer use ``u"..."`` literals for Unicode text. However,
+ you must use ``b"..."`` literals for binary data.
* Files opened as text files (still the default mode for :func:`open`)
always use an encoding to map between strings (in memory) and bytes
@@ -167,6 +171,50 @@
don't have functionality enough in common to warrant a shared base
class.
+* All backslashes in raw strings are interpreted literally. This
+ means that ``'\U'`` and ``'\u'`` escapes in raw strings are not
+ treated specially.
+
+XXX Deal with dupes below
+
+* There is only one text string type; its name is :class:`str` but its
+ behavior and implementation are like :class:`unicode` in 2.x.
+
+* The :class:`basestring` superclass has been removed. The ``2to3``
+ tool (see below) replaces every occurrence of :class:`basestring`
+ with :class:`str`.
+
+* :pep:`3137`: There is a new type, :class:`bytes`, to represent
+ binary data (and encoded text, which is treated as binary data until
+ it is decoded). The :class:`str` and :class:`bytes` types cannot be
+ mixed; you must always explicitly convert between them, using the
+ :meth:`str.encode` (str -> bytes) or :meth:`bytes.decode` (bytes ->
+ str) methods.
+
+* Like :class:`str`, the :class:`bytes` type is immutable. There is a
+ separate *mutable* type to hold buffered binary data,
+ :class:`bytearray`. Nearly all APIs that accept :class:`bytes` also
+ accept :class:`bytearray`. The mutable API is based on
+ :class:`collections.MutableSequence`.
+
+* :pep:`3138`: The :func:`repr` of a string no longer escapes
+ non-ASCII characters. It still escapes control characters and code
+ points with non-printable status in the Unicode standard, however.
+
+* :pep:`3120`: The default source encoding is now UTF-8.
+
+* :pep:`3131`: Non-ASCII letters are now allowed in identifiers.
+ (However, the standard library remains ASCII-only with the exception
+ of contributor names in comments.)
+
+* :pep:`3116`: New I/O implementation. The API is nearly 100%
+ backwards compatible, but completely reimplemented (currently largely
+ in Python). Also, binary files use bytes instead of strings.
+
+* The :mod:`StringIO` and :mod:`cStringIO` modules are gone. Instead,
+ import :class:`io.StringIO` or :class:`io.BytesIO`, for text and
+ data respectively.
+
* See also the :ref:`unicode-howto`, which was updated for Python 3.0.
Views And Iterators Instead Of Lists
@@ -254,8 +302,8 @@
This section gives a brief overview of every *syntactic* change in
Python 3.0.
-Additions
----------
+New Syntax
+----------
* :pep:`3107`: Function argument and return value annotations. This
provides a standardized way of annotating a function's parameters
@@ -304,8 +352,8 @@
* Bytes literals are introduced with a leading ``b`` or ``B``.
-Changes
--------
+Changed Syntax
+--------------
* New :keyword:`raise` statement syntax: ``raise [expr [from expr]]``.
Also note that string exceptions are no longer legal (:pep:`0352`).
@@ -333,8 +381,8 @@
*must* now be spelled as ``...``. (Previously it could also be
spelled as ``. . .``, by a mere accident of the grammar.)
-Removals
---------
+Removed Syntax
+--------------
* :pep:`3113`: Tuple parameter unpacking removed. You can no longer
write ``def foo(a, (b, c)): ...``.
@@ -362,7 +410,6 @@
(:pep:`0328`)
-
Changes Already Present In Python 2.6
=====================================
@@ -401,8 +448,7 @@
* :ref:`pep-3112`. The ``b"..."`` string literal notation (and its
variants like ``b'...'``, ``b"""..."""``, and ``br"..."``) now
- produces a literal of type :class:`bytes`. More about
- :class:`bytes` below.
+ produces a literal of type :class:`bytes`.
* :ref:`pep-3116`. The :mod:`io` module is now the standard way of
doing file I/O, and the initial values of :data:`sys.stdin`,
@@ -411,14 +457,17 @@
alias for :func:`io.open` and has additional keyword arguments
*encoding*, *errors*, *newline* and *closefd*. Also note that an
invalid *mode* argument now raises :exc:`ValueError`, not
- :exc:`IOError`.
+ :exc:`IOError`. The binary file object underlying a text file
+ object can be accessed as :attr:`f.buffer` (but beware that the
+ text object maintains a buffer of itself in order to speed up
+ the encoding and decoding operations).
* :ref:`pep-3118`. The old builtin :func:`buffer` is now really gone;
the new builtin :func:`memoryview` provides (mostly) similar
functionality.
* :ref:`pep-3119`. The :mod:`abc` module and the ABCs defined in the
- :mod:`collections` module plays a slightly more prominent role in
+ :mod:`collections` module plays a somewhat more prominent role in
the language now, and builtin collection types like :class:`dict`
and :class:`list` conform to the :class:`collections.MutableMapping`
and :class:`collections.MutableSequence` ABC, respectively.
@@ -427,11 +476,11 @@
notation is the only one supported, and binary literals have been
added.
-* :ref:`pep-3129`. This speaks for itself.
+* :ref:`pep-3129`.
* :ref:`pep-3141`. The :mod:`numbers` module is another new use of
ABCs, defining Python's "numeric tower". Also note the new
- :mod:`fractions` module.
+ :mod:`fractions` module which implements :class:`numbers.Rational`.
Library Changes
@@ -532,58 +581,14 @@
* Cleanup of the :mod:`random` module: removed the :func:`jumpahead` API.
-Strings And Bytes
-=================
-
-This section discusses the many changes in string XXX
-
-* There is only one string type; its name is :class:`str` but its behavior and
- implementation are like :class:`unicode` in 2.x.
-
-* The :class:`basestring` superclass has been removed. The ``2to3`` tool
- replaces every occurrence of :class:`basestring` with :class:`str`.
-
-* :pep:`3137`: There is a new type, :class:`bytes`, to represent
- binary data (and encoded text, which is treated as binary data until
- you decide to decode it). The :class:`str` and :class:`bytes` types
- cannot be mixed; you must always explicitly convert between them,
- using the :meth:`str.encode` (str -> bytes) or :meth:`bytes.decode`
- (bytes -> str) methods.
-
-.. XXX add bytearray
-
-* All backslashes in raw strings are interpreted literally. This means that
- ``'\U'`` and ``'\u'`` escapes in raw strings are not treated specially.
-
-* :pep:`3138`: :func:`repr` of a string no longer escapes all
- non-ASCII characters. XXX
-
-* :pep:`3112`: Bytes literals, e.g. ``b"abc"``, create :class:`bytes`
- instances.
-
-* :pep:`3120`: UTF-8 default source encoding.
-
-* :pep:`3131`: Non-ASCII identifiers. (However, the standard library remains
- ASCII-only with the exception of contributor names in comments.)
-
-* :pep:`3116`: New I/O Implementation. The API is nearly 100% backwards
- compatible, but completely reimplemented (currently mostly in Python). Also,
- binary files use bytes instead of strings.
-
-* The :mod:`StringIO` and :mod:`cStringIO` modules are gone. Instead, import
- :class:`io.StringIO` or :class:`io.BytesIO`.
-
-
-
:pep:`3101`: A New Approach To String Formatting
================================================
* A new system for built-in string formatting operations replaces the
``%`` string formatting operator. (However, the ``%`` operator is
still supported; it will be deprecated in Python 3.1 and removed
- from the language at some later time.)
-
-.. XXX expand this
+ from the language at some later time.) Read :pep:`3101` for the full
+ scoop.
:pep:`3106`: Revamping dict :meth:`dict.keys`, :meth:`dict.items` and :meth:`dict.values`
@@ -632,16 +637,24 @@
New Class And Metaclass Stuff
=============================
+XXX Move to new syntax section???
+
* Classic classes are gone.
-* :pep:`3115`: New Metaclass Syntax.
+* :pep:`3115`: New Metaclass Syntax. Instead of::
+
+ class C:
+ __metaclass__ = M
+ ...
-* :pep:`3119`: Abstract Base Classes (ABCs); ``@abstractmethod`` and
- ``@abstractproperty`` decorators; collection ABCs.
+ you now use::
-* :pep:`3129`: Class decorators.
+ class C(metaclass=M):
+ ...
-* :pep:`3141`: Numeric ABCs.
+ The module-global :data:`__metaclass__` variable is no longer supported.
+ (It was a crutch to make it easier to default to new-style classes
+ without deriving every class from :class:`object`.)
Other Language Changes
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