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| -rw-r--r-- | Doc/whatsnew/3.0.rst | 274 |
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diff --git a/Doc/whatsnew/3.0.rst b/Doc/whatsnew/3.0.rst index ac82317..e804bb1 100644 --- a/Doc/whatsnew/3.0.rst +++ b/Doc/whatsnew/3.0.rst @@ -2,7 +2,7 @@ What's New in Python 3.0 **************************** -:Author: A.M. Kuchling +:Author: A.M. Kuchling, Guido van Rossum .. |release| replace:: 0.0 @@ -48,14 +48,16 @@ .. % This saves the maintainer the effort of going through the SVN log .. % when researching a change. -This article explains the new features in Python 3.0. No release date for -Python 3.0 has been set; it will probably be released in mid 2008. +This article explains the new features in Python 3.0, comparing to 2.6 +(or in some cases 2.5, since 2.6 isn't released yet). -This article doesn't attempt to provide a complete specification of the new -features, but instead provides a convenient overview. For full details, you -should refer to the documentation for Python 3.0. If you want to understand the -complete implementation and design rationale, refer to the PEP for a particular -new feature. +The best estimate for a release date is August 2008. + +This article doesn't attempt to provide a complete specification of +the new features, but instead provides a convenient overview. For +full details, you should refer to the documentation for Python 3.0. If +you want to understand the complete implementation and design +rationale, refer to the PEP for a particular new feature. .. % Compare with previous release in 2 - 3 sentences here. .. % add hyperlink when the documentation becomes available online. @@ -68,12 +70,224 @@ new feature. .. % ====================================================================== +Common Stumbling Blocks +======================= + +This section briefly lists the changes that are more likely to trip +people up, without necessarily raising obvious errors. These are all +explained in more detail below. (I'm not listing syntactic changes +and removed or renamed features here, since those tend to produce hard +and fast errors; it's the subtle behavioral changes in code that +remains syntactically valid that trips people up. I'm also omitting +changes to rarely used features.) + +* Python 3.0 uses strings and bytes instead of the Unicode strings and + 8-bit strings. This means that pretty much all code that uses + Unicode, encodings or binary data in any way 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. + +* Text files enforce an encoding; binary files use bytes. This means + that if a file is opened using an incorrect mode or encoding, I/O + will likely fail. + +* Bytes aren't hashable, and don't support certain operations like + ``b.lower()``, ``b.strip()`` or ``b.split()``. + For the latter two, use ``b.strip(b" \t\r\n\f")`` or + ``b.split(b" \t\r\n\f")``. + +* ``map()`` and ``filter()`` return iterators. A quick fix is e.g. + ``list(map(...))``, but a better fix is often to use a list + comprehension (especially when the original code uses ``lambda``). + Particularly tricky is ``map()`` invoked for the side effects of the + function; the correct transformation is to use a for-loop. + +* ``dict`` methods ``.keys()``, ``.items()`` and ``.values()`` return + views instead of lists. For example, this no longer works: + ``k = d.keys(); k.sort()``. Use ``k = sorted(d)`` instead. + +* ``1/2`` returns a float. Use ``1//2`` to get the truncating behavior. + +* Code that unconditionally strips the trailing ``L`` from the ``repr()`` + of a long integer will chop off the last digit instead. + +* The ``print()`` function doesn't support the "softspace" feature of + the old ``print`` statement. For example, in Python 2.x, + ``print "A\n", "B\n"`` would write ``"A\nB\n"``; but in Python 3.0, + ``print("A\n", "B\n")`` writes ``"A\n B\n"``. + +* Also, ``print`` and ``print (x, y)`` behave differently without + warning: the former used to add a newline in 2.x, but does nothing + in 3.0; the latter used to print the ``repr()`` of a tuple in 2.x, + but prints the individual values in 3.0. + +* You'll be finding yourself typing ``print x`` a lot in interactive + mode. Time to retrain your fingers. :-) + + +Strings and Bytes +================= + +* There is only on string type; its name is ``str`` but its behavior + and implementation are more like ``unicode`` in 2.x. + +* PEP 358: There is a new type, ``bytes``, to represent binary data + (and encoded text, which is treated as binary data until you decide + to decode it). The ``str`` and ``bytes`` types cannot be mixed; you + must always explicitly convert between them, using the ``.encode()`` + (str -> bytes) or ``.decode()`` (bytes -> str) methods. Comparing a + bytes and a str instance for equality raises a TypeError; this + catches common mistakes. + +* PEP 3112: Bytes literals. E.g. b"abc". + +* 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 ``StringIO`` and ``cStringIO`` modules are gone. Instead, + import ``StringIO`` or ``BytesIO`` from the ``io`` module. + + +PEP 3101: A New Approach to String Formatting +============================================= + +XXX + + +PEP 3106: Revamping ``.keys()``, ``.items()`` and ``.values()`` +=============================================================== + +XXX + + +PEP 3107: Function Annotations +============================== + +XXX + + +Exception Stuff +=============== + +* PEP 352: Exceptions must derive from BaseException. This is the + root of the exception hierarchy; only Exception, + +* StandardException was removed (already in 2.6). + +* Dropping sequence behavior and ``.message`` attribute of exception + instances. + +* PEP 3109: Raising exceptions. You must now use ``raise + Exception(args)`` instead of ``raise Exception, args``. + +* PEP 3110: Catching exceptions. + +* PEP 3134: Exception chaining. (The ``__context__`` feature from the + PEP hasn't been implemented yet in 3.0a1.) + + +New Class and Metaclass Stuff +============================= + +* Classic classes are gone. + +* PEP 3115: New Metaclass Syntax. + +* PEP 3119: Abstract Base Classes; ``@abstractmethod`` and + ``@abstractproperty`` decorators; collection ABCs. + +* PEP 3129: Class decorators. + +* PEP 3141: Numeric ABCs. + + Other Language Changes ====================== -Here are all of the changes that Python 2.6 makes to the core Python language. +Here are most of the changes that Python 3.0 makes to the core Python +language and built-in functions. + +* Removed backticks (use ``repr()`` instead). + +* Removed ``<>`` (use ``!=`` instead). + +* ``as`` and ``with`` are keywords. + +* PEP 237: ``long`` renamed to ``int``. That is, there is only one + built-in integral type, named ``int``; but it behaves like the old + ``long`` type. + +* PEP 238: int division returns a float. + +* The ordering operators behave differently: for example, ``x < y`` + where ``x`` and ``y`` have incompatible types raises ``TypeError`` + instead of returning a pseudo-random boolean. + +* ``__getslice__()`` and friends killed. The syntax ``a[i:j]`` now + translates to ``a.__getitem__(slice(i, j))`` (or ``__setitem__`` + or ``__delitem``, depending on context). + +* PEP 3102: Keyword-only arguments. Named parameters occurring after + ``*args`` in the parameter list *must* be specified using keyword + syntax in the call. You can also use ``*`` in the parameter list to + indicate that you don't accept a variable-length argument list, but + you do have keyword-only arguments. + +* PEP 3104: ``nonlocal`` statement. Using ``nonlocal x`` you can now + assign directly to a variable in an outer (but non-global) scope. + +* PEP 3105: ``print`` is now a function. Keyword argumemts + ``file=sys.stdout``, ``sep=" "`` and ``end="\n"`` let you customize + it. + +* PEP 3111: ``raw_input()`` renamed to ``input()``. That is, the new + ``input()`` function reads a line from ``sys.stdin`` and returns it + with the trailing newline stripped. It raises ``EOFError`` if the + input is terminated prematurely. To get the old behavior of + ``input()``, use ``eval(input())``. + +* ``xrange()`` renamed to ``range()``. + +* PEP 3113: Tuple parameter unpacking removed. You can no longer write + ``def foo(a, (b, c)): ...``. Use ``def foo(a, b_c): b, c = b_c`` + instead. + +* PEP 3114: ``.next()`` renamed to ``.__next__()``. + +* PEP 3127: New octal literals; binary literals and ``bin()``. + Instead of ``0666``, you write ``0o666``. The oct() function is + modified accordingly. Also, ``0b1010`` equals 10, and ``bin(10)`` + returns ``"0b1010"``. + +* PEP 3132: Extended Iterable Unpacking. You can now write things + like ``a, b, *rest = some_sequence``. And even ``*rest, a = + stuff``. The ``rest`` variable is always a list; the right-hand + side may be any iterable. + +* PEP 3135: New ``super()``. You can now invoke ``super()`` without + arguments and the right class and instance will automatically be + chosen. With arguments, its behavior is unchanged. + +* ``zip()``, ``map()`` and ``filter()`` return iterators. + +* ``string.letters`` and its friends (``.lowercase`` and + ``.uppercase``) are gone. Use ``string.ascii_letters`` + etc. instead. + +* Removed: apply(), callable(), coerce(), execfile(), file(), + reduce(), reload(). + +* Removed: ``dict.has_key()``. + +* ``exec`` is now a function. -* Detailed changes are listed here. .. % ====================================================================== @@ -83,8 +297,9 @@ Optimizations * Detailed changes are listed here. -The net result of the 3.0 optimizations is that Python 3.0 runs the pystone -benchmark around XX% slower than Python 2.6. +The net result of the 3.0 generalizations is that Python 3.0 runs the +pystone benchmark around 25% slower than Python 2.5. There's room for +improvement! .. % ====================================================================== @@ -92,12 +307,14 @@ benchmark around XX% slower than Python 2.6. New, Improved, and Deprecated Modules ===================================== -As usual, Python's standard library received a number of enhancements and bug -fixes. Here's a partial list of the most notable changes, sorted alphabetically -by module name. Consult the :file:`Misc/NEWS` file in the source tree for a more -complete list of changes, or look through the CVS logs for all the details. +As usual, Python's standard library received a number of enhancements +and bug fixes. Here's a partial list of the most notable changes, +sorted alphabetically by module name. Consult the :file:`Misc/NEWS` +file in the source tree for a more complete list of changes, or look +through the CVS logs for all the details. -* Detailed changes are listed here. +* The ``cPickle`` module is gone. Use ``pickle`` instead. Eventually + we'll have a transparent accelerator module. .. % ====================================================================== .. % whole new modules get described in \subsections here @@ -110,7 +327,11 @@ Build and C API Changes Changes to Python's build process and to the C API include: -* Detailed changes are listed here. +* PEP 3118: New Buffer API. + +* PEP 3121: Extension Module Initialization & Finalization. + +* PEP 3123: Making PyObject_HEAD conform to standard C. .. % ====================================================================== @@ -128,10 +349,10 @@ Platform-specific changes go here. Other Changes and Fixes ======================= -As usual, there were a bunch of other improvements and bugfixes scattered -throughout the source tree. A search through the change logs finds there were -XXX patches applied and YYY bugs fixed between Python 2.6 and 3.0. Both figures -are likely to be underestimates. +As usual, there were a bunch of other improvements and bugfixes +scattered throughout the source tree. A search through the change +logs finds there were XXX patches applied and YYY bugs fixed between +Python 2.6 and 3.0. Both figures are likely to be underestimates. Some of the more notable changes are: @@ -143,8 +364,8 @@ Some of the more notable changes are: Porting to Python 3.0 ===================== -This section lists previously described changes that may require changes to your -code: +This section lists previously described changes that may require +changes to your code: * Everything is all in the details! @@ -156,6 +377,7 @@ code: Acknowledgements ================ -The author would like to thank the following people for offering suggestions, -corrections and assistance with various drafts of this article: . +The author would like to thank the following people for offering +suggestions, corrections and assistance with various drafts of this +article: . |