What's New in Python 2.2a1?

===========================

Core

- Generators were added; this is a new way to create an iterator (see

below) using what looks like a simple function containing one or

more 'yield' statements. See PEP 255. Since this adds a new

keyword to the language, this feature must be enabled by including a

future statement: "from __future__ import generators" (see PEP 236).

Generators will become a standard feature in a future release

(probably 2.3). Without this future statement, 'yield' remains an

ordinary identifier, but a warning is issued each time it is used.

(These warnings currently don't conform to the warnings framework of

PEP 230; we intend to fix this in 2.2a2.)

- The UTF-16 codec was modified to be more RFC compliant. It will now

only remove BOM characters at the start of the string and then

only if running in native mode (UTF-16-LE and -BE won't remove a

leading BMO character).

- Strings now have a new method .decode() to complement the already

existing .encode() method. These two methods provide direct access

to the corresponding decoders and encoders of the registered codecs.

To enhance the usability of the .encode() method, the special

casing of Unicode object return values was dropped (Unicode objects

were auto-magically converted to string using the default encoding).

Both methods will now return whatever the codec in charge of the

requested encoding returns as object, e.g. Unicode codecs will

return Unicode objects when decoding is requested ("äöü".decode("latin-1")

will return u"äöü"). This enables codec writer to create codecs

for various simple to use conversions.

New codecs were added to demonstrate these new features (the .encode()

and .decode() columns indicate the type of the returned objects):

Name | .encode() | .decode() | Description

----------------------------------------------------------------------

uu | string | string | UU codec (e.g. for email)

base64 | string | string | base64 codec

quopri | string | string | quoted-printable codec

zlib | string | string | zlib compression

hex | string | string | 2-byte hex codec

rot-13 | string | Unicode | ROT-13 Unicode charmap codec

- Some operating systems now support the concept of a default Unicode

encoding for file system operations. Notably, Windows supports 'mbcs'

as the default. The Macintosh will also adopt this concept in the medium

term, although the default encoding for that platform will be other than

'mbcs'.

On operating system that support non-ASCII filenames, it is common for

functions that return filenames (such as os.listdir()) to return Python

string objects pre-encoded using the default file system encoding for

the platform. As this encoding is likely to be different from Python's

default encoding, converting this name to a Unicode object before passing

it back to the Operating System would result in a Unicode error, as Python

would attempt to use its default encoding (generally ASCII) rather than

the default encoding for the file system.

In general, this change simply removes surprises when working with

Unicode and the file system, making these operations work as you expect,

increasing the transparency of Unicode objects in this context.

See [????] for more details, including examples.

- Float (and complex) literals in source code were evaluated to full

precision only when running from a .py file; the same code loaded from a

.pyc (or .pyo) file could suffer numeric differences starting at about the

12th significant decimal digit. For example, on a machine with IEEE-754

floating arithmetic,

x = 9007199254740992.0

print long(x)

printed 9007199254740992 if run directly from .py, but 9007199254740000

if from a compiled (.pyc or .pyo) file. This was due to marshal using

str(float) instead of repr(float) when building code objects. marshal

now uses repr(float) instead, which should reproduce floats to full

machine precision (assuming the platform C float<->string I/O conversion

functions are of good quality).

This may cause floating-point results to change in some cases, and

usually for the better, but may also cause numerically unstable

algorithms to break.

- The implementation of dicts suffers fewer collisions, which has speed

benefits. However, the order in which dict entries appear in dict.keys(),

dict.values() and dict.items() may differ from previous releases for a

given dict. Nothing is defined about this order, so no program should

rely on it. Nevertheless, it's easy to write test cases that rely on the

order by accident, typically because of printing the str() or repr() of a

dict to an "expected results" file. See Lib/test/test_support.py's new

sortdict(dict) function for a simple way to display a dict in sorted

order.

- Many other small changes to dicts were made, resulting in faster

operation along the most common code paths.

- Dictionary objects now support the "in" operator: "x in dict" means

the same as dict.has_key(x).

- The update() method of dictionaries now accepts generic mapping

objects. Specifically the argument object must support the .keys()

and __getitem__() methods. This allows you to say, for example,

{}.update(UserDict())

- Iterators were added; this is a generalized way of providing values

to a for loop. See PEP 234. There's a new built-in function iter()

to return an iterator. There's a new protocol to get the next value

from an iterator using the next() method (in Python) or the

tp_iternext slot (in C). There's a new protocol to get iterators

using the __iter__() method (in Python) or the tp_iter slot (in C).

Iterating (i.e. a for loop) over a dictionary generates its keys.

Iterating over a file generates its lines.

- The following functions were generalized to work nicely with iterator

arguments:

map(), filter(), reduce(), zip()

list(), tuple() (PySequence_Tuple() and PySequence_Fast() in C API)

max(), min()

join() method of strings

extend() method of lists

'x in y' and 'x not in y' (PySequence_Contains() in C API)

operator.countOf() (PySequence_Count() in C API)

right-hand side of assignment statements with multiple targets, such as

x, y, z = some_iterable_object_returning_exactly_3_values

- Accessing module attributes is significantly faster (for example,

random.random or os.path or yourPythonModule.yourAttribute).

- Comparing dictionary objects via == and != is faster, and now works even

if the keys and values don't support comparisons other than ==.

- Comparing dictionaries in ways other than == and != is slower: there were

insecurities in the dict comparison implementation that could cause Python

to crash if the element comparison routines for the dict keys and/or

values mutated the dicts. Making the code bulletproof slowed it down.

- Collisions in dicts are resolved via a new approach, which can help

dramatically in bad cases. For example, looking up every key in a dict

d with d.keys() == [i << 16 for i in range(20000)] is approximately 500x

faster now. Thanks to Christian Tismer for pointing out the cause and

the nature of an effective cure (last December! better late than never).

- repr() is much faster for large containers (dict, list, tuple).

Library

- The flags used in dlopen calls can now be configured using

sys.setdlopenflags and queried using sys.getdlopenflags.

- Fredrik Lundh's xmlrpclib is now a standard library module. This

provides full client-side XML-RPC support. In addition,

Demo/xmlrpc/ contains two server frameworks (one SocketServer-based,

one asyncore-based). Thanks to Eric Raymond for the documentation.

- The xrange() object is simplified: it no longer supports slicing,

repetition, comparisons, efficient 'in' checking, the tolist()

method, or the start, stop and step attributes. See PEP 260.

- A new function fnmatch.filter to filter lists of file names was added.

- calendar.py uses month and day names based on the current locale.

- strop is now *really* obsolete (this was announced before with 1.6),

and issues DeprecationWarning when used (except for the four items

that are still imported into string.py).

- Cookie.py now sorts key+value pairs by key in output strings.

- pprint.isrecursive(object) didn't correctly identify recursive objects.

Now it does.

- pprint functions now much faster for large containers (tuple, list, dict).

- New 'q' and 'Q' format codes in the struct module, corresponding to C

types "long long" and "unsigned long long" (on Windows, __int64). In

native mode, these can be used only when the platform C compiler supports

these types (when HAVE_LONG_LONG is #define'd by the Python config

process), and then they inherit the sizes and alignments of the C types.

In standard mode, 'q' and 'Q' are supported on all platforms, and are

8-byte integral types.

- The site module installs a new built-in function 'help' that invokes

pydoc.help. It must be invoked as 'help()'; when invoked as 'help',

it displays a message reminding the user to use 'help()' or

'help(object)'.

Tests

- New test_mutants.py runs dict comparisons where the key and value

comparison operators mutute the dicts randomly during comparison. This

rapidly causes Python to crash under earlier releases (not for the faint

of heart: it can also cause Win9x to freeze or reboot!).

- New test_pprint.py verfies that pprint.isrecursive() and

pprint.isreadable() return sensible results. Also verifies that simple

cases produce correct output.

New platforms

- Python should compile and run out of the box using the Borland C

compiler (under Windows), thanks to Stephen Hansen.

C API

- Removed the unused last_is_sticky argument from the internal

_PyTuple_Resize(). If this affects you, you were cheating.

======================================================================

What's New in Python 2.1 (final)?

=================================

We only changed a few things since the last release candidate, all in

Python library code:

- A bug in the locale module was fixed that affected locales which

define no grouping for numeric formatting.

- A few bugs in the weakref module's implementations of weak

dictionaries (WeakValueDictionary and WeakKeyDictionary) were fixed,

and the test suite was updated to check for these bugs.

- An old bug in the os.path.walk() function (introduced in Python

2.0!) was fixed: a non-existent file would cause an exception

instead of being ignored.

- Fixed a few bugs in the new symtable module found by Neil Norwitz's

PyChecker.

What's New in Python 2.1c2?

===========================

A flurry of small changes, and one showstopper fixed in the nick of

time made it necessary to release another release candidate. The list

here is the *complete* list of patches (except version updates):

Core

- Tim discovered a nasty bug in the dictionary code, caused by

PyDict_Next() calling dict_resize(), and the GC code's use of

PyDict_Next() violating an assumption in dict_items(). This was

fixed with considerable amounts of band-aid, but the net effect is a

saner and more robust implementation.

- Made a bunch of symbols static that were accidentally global.

Build and Ports

- The setup.py script didn't check for a new enough version of zlib

(1.1.3 is needed). Now it does.

- Changed "make clean" target to also remove shared libraries.

- Added a more general warning about the SGI Irix optimizer to README.

Library

- Fix a bug in urllib.basejoin("http://host", "../file.html") which

omitted the slash between host and file.html.

- The mailbox module's _Mailbox class contained a completely broken

and undocumented seek() method. Ripped it out.

- Fixed a bunch of typos in various library modules (urllib2, smtpd,

sgmllib, netrc, chunk) found by Neil Norwitz's PyChecker.

- Fixed a few last-minute bugs in unittest.

Extensions

- Reverted the patch to the OpenSSL code in socketmodule.c to support

RAND_status() and the EGD, and the subsequent patch that tried to

fix it for pre-0.9.5 versions; the problem with the patch is that on

some systems it issues a warning whenever socket is imported, and

that's unacceptable.

Tests

- Fixed the pickle tests to work with "import test.test_pickle".

- Tweaked test_locale.py to actually run the test Windows.

- In distutils/archive_util.py, call zipfile.ZipFile() with mode "w",

not "wb" (which is not a valid mode at all).

- Fix pstats browser crashes. Import readline if it exists to make

the user interface nicer.

- Add "import thread" to the top of test modules that import the

threading module (test_asynchat and test_threadedtempfile). This

prevents test failures caused by a broken threading module resulting

from a previously caught failed import.

- Changed test_asynchat.py to set the SO_REUSEADDR option; this was

needed on some platforms (e.g. Solaris 8) when the tests are run

twice in succession.

- Skip rather than fail test_sunaudiodev if no audio device is found.

What's New in Python 2.1c1?

===========================

This list was significantly updated when 2.1c2 was released; the 2.1c1

release didn't mention most changes that were actually part of 2.1c1:

Legal

- Copyright was assigned to the Python Software Foundation (PSF) and a

PSF license (very similar to the CNRI license) was added.

- The CNRI copyright notice was updated to include 2001.

Core

- After a public outcry, assignment to __debug__ is no longer illegal;

instead, a warning is issued. It will become illegal in 2.2.

- Fixed a core dump with "%#x" % 0, and changed the semantics so that

"%#x" now always prepends "0x", even if the value is zero.

- Fixed some nits in the bytecode compiler.

- Fixed core dumps when calling certain kinds of non-functions.

- Fixed various core dumps caused by reference count bugs.

Build and Ports

- Use INSTALL_SCRIPT to install script files.

- New port: SCO Unixware 7, by Billy G. Allie.

- Updated RISCOS port.

- Updated BeOS port and notes.

- Various other porting problems resolved.

Library

- The TERMIOS and SOCKET modules are now truly obsolete and

unnecessary. Their symbols are incorporated in the termios and

socket modules.

- Fixed some 64-bit bugs in pickle, cPickle, and struct, and added

better tests for pickling.

- threading: make Condition.wait() robust against KeyboardInterrupt.

- zipfile: add support to zipfile to support opening an archive

represented by an open file rather than a file name. Fix bug where

the archive was not properly closed. Fixed a bug in this bugfix

where flush() was called for a read-only file.

- imputil: added an uninstall() method to the ImportManager.

- Canvas: fixed bugs in lower() and tkraise() methods.

- SocketServer: API change (added overridable close_request() method)

so that the TCP server can explicitly close the request.

- pstats: Eric Raymond added a simple interactive statistics browser,

invoked when the module is run as a script.

- locale: fixed a problem in format().

- webbrowser: made it work when the BROWSER environment variable has a

value like "/usr/bin/netscape". Made it auto-detect Konqueror for

KDE 2. Fixed some other nits.

- unittest: changes to allow using a different exception than

AssertionError, and added a few more function aliases. Some other

small changes.

- urllib, urllib2: fixed redirect problems and a coupleof other nits.

- asynchat: fixed a critical bug in asynchat that slipped through the

2.1b2 release. Fixed another rare bug.

- Fix some unqualified except: clauses (always a bad code example).

XML

- pyexpat: new API get_version_string().

- Fixed some minidom bugs.

Extensions

- Fixed a core dump in _weakref. Removed the weakref.mapping()

function (it adds nothing to the API).

- Rationalized the use of header files in the readline module, to make

it compile (albeit with some warnings) with the very recent readline

4.2, without breaking for earlier versions.

- Hopefully fixed a buffering problem in linuxaudiodev.

- Attempted a fix to make the OpenSSL support in the socket module

work again with pre-0.9.5 versions of OpenSSL.

Tests

- Added a test case for asynchat and asyncore.

- Removed coupling between tests where one test failing could break

another.

Tools

- Ping added an interactive help browser to pydoc, fixed some nits

in the rest of the pydoc code, and added some features to his

inspect module.

- An updated python-mode.el version 4.1 which integrates Ken

Manheimer's pdbtrack.el. This makes debugging Python code via pdb

much nicer in XEmacs and Emacs. When stepping through your program

with pdb, in either the shell window or the *Python* window, the

source file and line will be tracked by an arrow. Very cool!

- IDLE: syntax warnings in interactive mode are changed into errors.

- Some improvements to Tools/webchecker (ignore some more URL types,

follow some more links).

- Brought the Tools/compiler package up to date.

What's New in Python 2.1 beta 2?

================================

(Unlisted are many fixed bugs, more documentation, etc.)

Core language, builtins, and interpreter

- The nested scopes work (enabled by "from __future__ import

nested_scopes") is completed; in particular, the future now extends

into code executed through exec, eval() and execfile(), and into the

interactive interpreter.

- When calling a base class method (e.g. BaseClass.__init__(self)),

this is now allowed even if self is not strictly spoken a class

instance (e.g. when using metaclasses or the Don Beaudry hook).

- Slice objects are now comparable but not hashable; this prevents

dict[:] from being accepted but meaningless.

- Complex division is now calculated using less braindead algorithms.

This doesn't change semantics except it's more likely to give useful

results in extreme cases. Complex repr() now uses full precision

like float repr().

- sgmllib.py now calls handle_decl() for simple <!...> declarations.

- It is illegal to assign to the name __debug__, which is set when the

interpreter starts. It is effectively a compile-time constant.

- A warning will be issued if a global statement for a variable

follows a use or assignment of that variable.

Standard library

- unittest.py, a unit testing framework by Steve Purcell (PyUNIT,

inspired by JUnit), is now part of the standard library. You now

have a choice of two testing frameworks: unittest requires you to

write testcases as separate code, doctest gathers them from

docstrings. Both approaches have their advantages and

disadvantages.

- A new module Tix was added, which wraps the Tix extension library

for Tk. With that module, it is not necessary to statically link

Tix with _tkinter, since Tix will be loaded with Tcl's "package

require" command. See Demo/tix/.

- tzparse.py is now obsolete.

- In gzip.py, the seek() and tell() methods are removed -- they were

non-functional anyway, and it's better if callers can test for their

existence with hasattr().

Python/C API

- PyDict_Next(): it is now safe to call PyDict_SetItem() with a key

that's already in the dictionary during a PyDict_Next() iteration.

This used to fail occasionally when a dictionary resize operation

could be triggered that would rehash all the keys. All other

modifications to the dictionary are still off-limits during a

PyDict_Next() iteration!

- New extended APIs related to passing compiler variables around.

- New abstract APIs PyObject_IsInstance(), PyObject_IsSubclass()

implement isinstance() and issubclass().

- Py_BuildValue() now has a "D" conversion to create a Python complex

number from a Py_complex C value.

- Extensions types which support weak references must now set the

field allocated for the weak reference machinery to NULL themselves;

this is done to avoid the cost of checking each object for having a

weakly referencable type in PyObject_INIT(), since most types are

not weakly referencable.

- PyFrame_FastToLocals() and PyFrame_LocalsToFast() copy bindings for

free variables and cell variables to and from the frame's f_locals.

- Variants of several functions defined in pythonrun.h have been added

to support the nested_scopes future statement. The variants all end

in Flags and take an extra argument, a PyCompilerFlags *; examples:

PyRun_AnyFileExFlags(), PyRun_InteractiveLoopFlags(). These

variants may be removed in Python 2.2, when nested scopes are

mandatory.

Distutils

- the sdist command now writes a PKG-INFO file, as described in PEP 241,

into the release tree.

- several enhancements to the bdist_wininst command from Thomas Heller

(an uninstaller, more customization of the installer's display)

- from Jack Jansen: added Mac-specific code to generate a dialog for

users to specify the command-line (because providing a command-line with

MacPython is awkward). Jack also made various fixes for the Mac

and the Metrowerks compiler.

- added 'platforms' and 'keywords' to the set of metadata that can be

specified for a distribution.

- applied patches from Jason Tishler to make the compiler class work with

Cygwin.

What's New in Python 2.1 beta 1?

================================

Core language, builtins, and interpreter

- Following an outcry from the community about the amount of code

broken by the nested scopes feature introduced in 2.1a2, we decided

to make this feature optional, and to wait until Python 2.2 (or at

least 6 months) to make it standard. The option can be enabled on a

per-module basis by adding "from __future__ import nested_scopes" at

the beginning of a module (before any other statements, but after

comments and an optional docstring). See PEP 236 (Back to the

__future__) for a description of the __future__ statement. PEP 227

(Statically Nested Scopes) has been updated to reflect this change,

and to clarify the semantics in a number of endcases.

- The nested scopes code, when enabled, has been hardened, and most

bugs and memory leaks in it have been fixed.

- Compile-time warnings are now generated for a number of conditions

that will break or change in meaning when nested scopes are enabled:

- Using "from...import *" or "exec" without in-clause in a function

scope that also defines a lambda or nested function with one or

more free (non-local) variables. The presence of the import* or

bare exec makes it impossible for the compiler to determine the

exact set of local variables in the outer scope, which makes it

impossible to determine the bindings for free variables in the

inner scope. To avoid the warning about import *, change it into

an import of explicitly name object, or move the import* statement

to the global scope; to avoid the warning about bare exec, use

exec...in... (a good idea anyway -- there's a possibility that

bare exec will be deprecated in the future).

- Use of a global variable in a nested scope with the same name as a

local variable in a surrounding scope. This will change in

meaning with nested scopes: the name in the inner scope will

reference the variable in the outer scope rather than the global

of the same name. To avoid the warning, either rename the outer

variable, or use a global statement in the inner function.

- An optional object allocator has been included. This allocator is

optimized for Python objects and should be faster and use less memory

than the standard system allocator. It is not enabled by default

because of possible thread safety problems. The allocator is only

protected by the Python interpreter lock and it is possible that some

extension modules require a thread safe allocator. The object

allocator can be enabled by providing the "--with-pymalloc" option to

configure.

Standard library

- pyexpat now detects the expat version if expat.h defines it. A

number of additional handlers are provided, which are only available

since expat 1.95. In addition, the methods SetParamEntityParsing and

GetInputContext of Parser objects are available with 1.95.x

only. Parser objects now provide the ordered_attributes and

specified_attributes attributes. A new module expat.model was added,

which offers a number of additional constants if 1.95.x is used.

- xml.dom offers the new functions registerDOMImplementation and

getDOMImplementation.

- xml.dom.minidom offers a toprettyxml method. A number of DOM

conformance issues have been resolved. In particular, Element now

has an hasAttributes method, and the handling of namespaces was

improved.

- Ka-Ping Yee contributed two new modules: inspect.py, a module for

getting information about live Python code, and pydoc.py, a module

for interactively converting docstrings to HTML or text.

Tools/scripts/pydoc, which is now automatically installed into

<prefix>/bin, uses pydoc.py to display documentation; try running

"pydoc -h" for instructions. "pydoc -g" pops up a small GUI that

lets you browse the module docstrings using a web browser.

- New library module difflib.py, primarily packaging the SequenceMatcher

class at the heart of the popular ndiff.py file-comparison tool.

- doctest.py (a framework for verifying Python code examples in docstrings)

is now part of the std library.

Windows changes

- A new entry in the Start menu, "Module Docs", runs "pydoc -g" -- a

small GUI that lets you browse the module docstrings using your

default web browser.

- Import is now case-sensitive. PEP 235 (Import on Case-Insensitive

Platforms) is implemented. See

http://python.sourceforge.net/peps/pep-0235.html

for full details, especially the "Current Lower-Left Semantics" section.

The new Windows import rules are simpler than before:

A. If the PYTHONCASEOK environment variable exists, same as

before: silently accept the first case-insensitive match of any

kind; raise ImportError if none found.

B. Else search sys.path for the first case-sensitive match; raise

ImportError if none found.

The same rules have been implented on other platforms with case-

insensitive but case-preserving filesystems too (including Cygwin, and

several flavors of Macintosh operating systems).

- winsound module: Under Win9x, winsound.Beep() now attempts to simulate

what it's supposed to do (and does do under NT and 2000) via direct

port manipulation. It's unknown whether this will work on all systems,

but it does work on my Win98SE systems now and was known to be useless on

all Win9x systems before.

- Build: Subproject _test (effectively) renamed to _testcapi.

New platforms

- 2.1 should compile and run out of the box under MacOS X, even using HFS+.

Thanks to Steven Majewski!

- 2.1 should compile and run out of the box on Cygwin. Thanks to Jason

Tishler!

- 2.1 contains new files and patches for RISCOS, thanks to Dietmar

Schwertberger! See RISCOS/README for more information -- it seems

that because of the bizarre filename conventions on RISCOS, no port

to that platform is easy. Note that the new variable os.endsep is

silently supported in order to make life easier on this platform,

but we don't advertise it because it's not worth for most folks to

care about RISCOS portability.

What's New in Python 2.1 alpha 2?

=================================

Core language, builtins, and interpreter

- Scopes nest. If a name is used in a function or class, but is not

local, the definition in the nearest enclosing function scope will

be used. One consequence of this change is that lambda statements

could reference variables in the namespaces where the lambda is

defined. In some unusual cases, this change will break code.

In all previous version of Python, names were resolved in exactly

three namespaces -- the local namespace, the global namespace, and

the builtin namespace. According to this old definition, if a

function A is defined within a function B, the names bound in B are

not visible in A. The new rules make names bound in B visible in A,

unless A contains a name binding that hides the binding in B.

Section 4.1 of the reference manual describes the new scoping rules

in detail. The test script in Lib/test/test_scope.py demonstrates

some of the effects of the change.

The new rules will cause existing code to break if it defines nested

functions where an outer function has local variables with the same

name as globals or builtins used by the inner function. Example:

def munge(str):

def helper(x):

return str(x)

if type(str) != type(''):

str = helper(str)

return str.strip()

Under the old rules, the name str in helper() is bound to the

builtin function str(). Under the new rules, it will be bound to

the argument named str and an error will occur when helper() is

called.

- The compiler will report a SyntaxError if "from ... import *" occurs

in a function or class scope. The language reference has documented

that this case is illegal, but the compiler never checked for it.

The recent introduction of nested scope makes the meaning of this

form of name binding ambiguous. In a future release, the compiler

may allow this form when there is no possibility of ambiguity.

- repr(string) is easier to read, now using hex escapes instead of octal,

and using \t, \n and \r instead of \011, \012 and \015 (respectively):

>>> "\texample \r\n" + chr(0) + chr(255)

'\texample \r\n\x00\xff' # in 2.1

'\011example \015\012\000\377' # in 2.0

- Functions are now compared and hashed by identity, not by value, since

the func_code attribute is writable.

- Weak references (PEP 205) have been added. This involves a few

changes in the core, an extension module (_weakref), and a Python

module (weakref). The weakref module is the public interface. It

includes support for "explicit" weak references, proxy objects, and

mappings with weakly held values.

- A 'continue' statement can now appear in a try block within the body

of a loop. It is still not possible to use continue in a finally

clause.

Standard library

- mailbox.py now has a new class, PortableUnixMailbox which is

identical to UnixMailbox but uses a more portable scheme for

determining From_ separators. Also, the constructors for all the

classes in this module have a new optional `factory' argument, which

is a callable used when new message classes must be instantiated by

the next() method.

- random.py is now self-contained, and offers all the functionality of

the now-deprecated whrandom.py. See the docs for details. random.py

also supports new functions getstate() and setstate(), for saving

and restoring the internal state of the generator; and jumpahead(n),

for quickly forcing the internal state to be the same as if n calls to

random() had been made. The latter is particularly useful for multi-

threaded programs, creating one instance of the random.Random() class for

each thread, then using .jumpahead() to force each instance to use a

non-overlapping segment of the full period.

- random.py's seed() function is new. For bit-for-bit compatibility with

prior releases, use the whseed function instead. The new seed function

addresses two problems: (1) The old function couldn't produce more than

about 2**24 distinct internal states; the new one about 2**45 (the best

that can be done in the Wichmann-Hill generator). (2) The old function

sometimes produced identical internal states when passed distinct

integers, and there was no simple way to predict when that would happen;

the new one guarantees to produce distinct internal states for all

arguments in [0, 27814431486576L).

- The socket module now supports raw packets on Linux. The socket

family is AF_PACKET.

- test_capi.py is a start at running tests of the Python C API. The tests

are implemented by the new Modules/_testmodule.c.

- A new extension module, _symtable, provides provisional access to the

internal symbol table used by the Python compiler. A higher-level

interface will be added on top of _symtable in a future release.

- Removed the obsolete soundex module.

- xml.dom.minidom now uses the standard DOM exceptions. Node supports

the isSameNode method; NamedNodeMap the get method.

- xml.sax.expatreader supports the lexical handler property; it

generates comment, startCDATA, and endCDATA events.

Windows changes

- Build procedure: the zlib project is built in a different way that

ensures the zlib header files used can no longer get out of synch with

the zlib binary used. See PCbuild\readme.txt for details. Your old

zlib-related directories can be deleted; you'll need to download fresh

source for zlib and unpack it into a new directory.

- Build: New subproject _test for the benefit of test_capi.py (see above).

- Build: New subproject _symtable, for new DLL _symtable.pyd (a nascent

interface to some Python compiler internals).

- Build: Subproject ucnhash is gone, since the code was folded into the

unicodedata subproject.

What's New in Python 2.1 alpha 1?

=================================

Core language, builtins, and interpreter

- There is a new Unicode companion to the PyObject_Str() API

called PyObject_Unicode(). It behaves in the same way as the

former, but assures that the returned value is an Unicode object

(applying the usual coercion if necessary).

- The comparison operators support "rich comparison overloading" (PEP

207). C extension types can provide a rich comparison function in

the new tp_richcompare slot in the type object. The cmp() function

and the C function PyObject_Compare() first try the new rich

comparison operators before trying the old 3-way comparison. There

is also a new C API PyObject_RichCompare() (which also falls back on

the old 3-way comparison, but does not constrain the outcome of the

rich comparison to a Boolean result).

The rich comparison function takes two objects (at least one of

which is guaranteed to have the type that provided the function) and

an integer indicating the opcode, which can be Py_LT, Py_LE, Py_EQ,

Py_NE, Py_GT, Py_GE (for <, <=, ==, !=, >, >=), and returns a Python

object, which may be NotImplemented (in which case the tp_compare

slot function is used as a fallback, if defined).

Classes can overload individual comparison operators by defining one

or more of the methods__lt__, __le__, __eq__, __ne__, __gt__,

__ge__. There are no explicit "reflected argument" versions of

these; instead, __lt__ and __gt__ are each other's reflection,

likewise for__le__ and __ge__; __eq__ and __ne__ are their own

reflection (similar at the C level). No other implications are

made; in particular, Python does not assume that == is the Boolean

inverse of !=, or that < is the Boolean inverse of >=. This makes

it possible to define types with partial orderings.

Classes or types that want to implement (in)equality tests but not

the ordering operators (i.e. unordered types) should implement ==

and !=, and raise an error for the ordering operators.

It is possible to define types whose rich comparison results are not

Boolean; e.g. a matrix type might want to return a matrix of bits

for A < B, giving elementwise comparisons. Such types should ensure

that any interpretation of their value in a Boolean context raises

an exception, e.g. by defining __nonzero__ (or the tp_nonzero slot

at the C level) to always raise an exception.

- Complex numbers use rich comparisons to define == and != but raise

an exception for <, <=, > and >=. Unfortunately, this also means

that cmp() of two complex numbers raises an exception when the two

numbers differ. Since it is not mathematically meaningful to compare

complex numbers except for equality, I hope that this doesn't break

too much code.

- The outcome of comparing non-numeric objects of different types is

not defined by the language, other than that it's arbitrary but

consistent (see the Reference Manual). An implementation detail changed

in 2.1a1 such that None now compares less than any other object. Code

relying on this new behavior (like code that relied on the previous

behavior) does so at its own risk.

- Functions and methods now support getting and setting arbitrarily

named attributes (PEP 232). Functions have a new __dict__

(a.k.a. func_dict) which hold the function attributes. Methods get

and set attributes on their underlying im_func. It is a TypeError

to set an attribute on a bound method.

- The xrange() object implementation has been improved so that

xrange(sys.maxint) can be used on 64-bit platforms. There's still a

limitation that in this case len(xrange(sys.maxint)) can't be

calculated, but the common idiom "for i in xrange(sys.maxint)" will

work fine as long as the index i doesn't actually reach 2**31.

(Python uses regular ints for sequence and string indices; fixing

that is much more work.)

- Two changes to from...import:

1) "from M import X" now works even if (after loading module M)

sys.modules['M'] is not a real module; it's basically a getattr()

operation with AttributeError exceptions changed into ImportError.

2) "from M import *" now looks for M.__all__ to decide which names to

import; if M.__all__ doesn't exist, it uses M.__dict__.keys() but

filters out names starting with '_' as before. Whether or not

__all__ exists, there's no restriction on the type of M.

- File objects have a new method, xreadlines(). This is the fastest

way to iterate over all lines in a file:

for line in file.xreadlines():

...do something to line...

See the xreadlines module (mentioned below) for how to do this for

other file-like objects.

- Even if you don't use file.xreadlines(), you may expect a speedup on

line-by-line input. The file.readline() method has been optimized

quite a bit in platform-specific ways: on systems (like Linux) that

support flockfile(), getc_unlocked(), and funlockfile(), those are

used by default. On systems (like Windows) without getc_unlocked(),

a complicated (but still thread-safe) method using fgets() is used by

default.

You can force use of the fgets() method by #define'ing

USE_FGETS_IN_GETLINE at build time (it may be faster than

getc_unlocked()).

You can force fgets() not to be used by #define'ing

DONT_USE_FGETS_IN_GETLINE (this is the first thing to try if std test

test_bufio.py fails -- and let us know if it does!).

- In addition, the fileinput module, while still slower than the other

methods on most platforms, has been sped up too, by using

file.readlines(sizehint).

- Support for run-time warnings has been added, including a new

command line option (-W) to specify the disposition of warnings.

See the description of the warnings module below.

- Extensive changes have been made to the coercion code. This mostly

affects extension modules (which can now implement mixed-type

numerical operators without having to use coercion), but

occasionally, in boundary cases the coercion semantics have changed

subtly. Since this was a terrible gray area of the language, this

is considered an improvement. Also note that __rcmp__ is no longer

supported -- instead of calling __rcmp__, __cmp__ is called with

reflected arguments.

- In connection with the coercion changes, a new built-in singleton

object, NotImplemented is defined. This can be returned for

operations that wish to indicate they are not implemented for a

particular combination of arguments. From C, this is

Py_NotImplemented.

- The interpreter accepts now bytecode files on the command line even

if they do not have a .pyc or .pyo extension. On Linux, after executing

import imp,sys,string

magic = string.join(["\\x%.2x" % ord(c) for c in imp.get_magic()],"")

reg = ':pyc:M::%s::%s:' % (magic, sys.executable)

open("/proc/sys/fs/binfmt_misc/register","wb").write(reg)

any byte code file can be used as an executable (i.e. as an argument

to execve(2)).

- %[xXo] formats of negative Python longs now produce a sign

character. In 1.6 and earlier, they never produced a sign,

and raised an error if the value of the long was too large

to fit in a Python int. In 2.0, they produced a sign if and

only if too large to fit in an int. This was inconsistent

across platforms (because the size of an int varies across

platforms), and inconsistent with hex() and oct(). Example:

>>> "%x" % -0x42L

'-42' # in 2.1

'ffffffbe' # in 2.0 and before, on 32-bit machines

>>> hex(-0x42L)

'-0x42L' # in all versions of Python

The behavior of %d formats for negative Python longs remains

the same as in 2.0 (although in 1.6 and before, they raised

an error if the long didn't fit in a Python int).

%u formats don't make sense for Python longs, but are allowed

and treated the same as %d in 2.1. In 2.0, a negative long

formatted via %u produced a sign if and only if too large to

fit in an int. In 1.6 and earlier, a negative long formatted

via %u raised an error if it was too big to fit in an int.

- Dictionary objects have an odd new method, popitem(). This removes

an arbitrary item from the dictionary and returns it (in the form of

a (key, value) pair). This can be useful for algorithms that use a

dictionary as a bag of "to do" items and repeatedly need to pick one

item. Such algorithms normally end up running in quadratic time;

using popitem() they can usually be made to run in linear time.

Standard library

- In the time module, the time argument to the functions strftime,

localtime, gmtime, asctime and ctime is now optional, defaulting to

the current time (in the local timezone).

- The ftplib module now defaults to passive mode, which is deemed a

more useful default given that clients are often inside firewalls

these days. Note that this could break if ftplib is used to connect

to a *server* that is inside a firewall, from outside; this is

expected to be a very rare situation. To fix that, you can call

ftp.set_pasv(0).

- The module site now treats .pth files not only for path configuration,

but also supports extensions to the initialization code: Lines starting

with import are executed.

- There's a new module, warnings, which implements a mechanism for

issuing and filtering warnings. There are some new built-in

exceptions that serve as warning categories, and a new command line

option, -W, to control warnings (e.g. -Wi ignores all warnings, -We

turns warnings into errors). warnings.warn(message[, category])