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Notes

Python 2.1.3 Release Notes

Release date: 08-April-2002

What's new in Python 2.1.3 (final)?

Core

  • Fixed two bugs reported as SF #535905: under certain conditions, deallocating a deeply nested structure could cause a segfault in the garbage collector, due to interaction with the "trashcan" code; access to the current frame during destruction of a local variable could access a pointer to freed memory.
  • SF #457466: popenx() argument mangling hangs python (win9x only). Under certain circumstances, using any of the popen calls on win9x would cause python to hang.

Library

  • The xml.sax.expatreader.ExpatParser class will no longer create circular references by using itself as the locator that gets passed to the content handler implementation. [SF bug #535474]
  • A security hole ("double free") was found in zlib-1.1.3, a popular third party compression library used by some Python modules. The hole was quickly plugged in zlib-1.1.4, and the Windows build of Python now ships with zlib-1.1.4.

Windows

  • The installer now installs Start menu shortcuts under (the local equivalent of) "All Users" when doing an Admin install.
  • If you do what it takes to compile SSL support for Windows, a bug in httplib.py prevented SSL from working correctly. That bug has been fixed, but note that SSL support on Windows is still not enabled in this release.

What's New in Python 2.1.2 (final)?

Changes in metadata:

  • Fixed the version numbers in the LICENSE, and the copyright date in numerous places.
  • Fixed the instructions (in Doc/lib/libposix.tex) for building with Large Filesystem Support (LFS).
  • Added GetArgv() docs in Mac UI chapter.
  • Some fixes to the Misc/NEWS file (e.g. the note about the new 32-bit installer wasn't in the 2.1.2c1 release).

One code change:

  • Backported a bugfix for importdl.c, SF patch #471839: Bug when extensions import extensions.

What's New in Python 2.1.2 (rc1)?

  • The 32-bit Windows installer (new for 2.2) is now used for 2.1.2 too. This works much better on Windows 2000 and XP, especially if you don't have Administrator privileges.
  • The socket object gained a new method, 'sendall()'. This method is guaranteed to send all data - this is not guaranteed by the 'send()' method. See also SF patch #474307. The standard library has been updated to use this method where appropriate.

Many bugs were fixed. The following is a list of some of the major or notable fixes:

  • Fix for incorrectly swapped arguments to PyFrame_BlockSetup in ceval.c. This bug could cause python to crash. It was related to using a 'continue' inside a 'try' block.
  • SF bug #422004: Py_Initialise fix that allows reload(exceptions) to work - this is apparently very important for embedded python working with multiple interpreters.
  • SF patch #500401: webbrowser: tightened up the command passed to os.system() so that arbitrary shell code can't be executed because a bogus URL was passed in.
  • The Python compiler package was updated to correctly calculate stack depth in some cases. This was affecting Zope Python Scripts rather badly.
  • Largefile support was added (but not on by default, you'll need to follow the instructions in the documentation of the posix module).
  • SF bug #443120: Fix a cgi.py denial-of-service attack,
  • socketmodule's SSL_read and SSL_write now release the global interpreter lock.
  • threading uses the PTHREAD_SCOPE_SYSTEM attribute where available. This should remove the need to add tiny sleeps at the start of threads to allow other threads to be scheduled.
  • Lib/asyncore is now more defensive in select()
  • Lib/dumbdbm is now merely dumb, rather than terminally broken.
  • SF bug #441712: more liberal handling of ftp servers' 227 responses (don't require parentheses).
  • SF bug #440693: make sure zip files use "/" as directory separator.
  • If 'unittest.py' was run from the command line with the name of a test case class as a parameter, it failed with an ugly error.
  • SF bug #231249: cgi.py opens too many (temporary) files.
  • Lib/CGIHTTPServer.py supports binary data on Windows.
  • base64.encodestring/decodestring are much faster.
  • SF bug #471928: global made w/nested list comprehensions
  • SF patch #422106: fix segmentation fault in sys.displayhook
  • SF bug 476129: gc.collect sometimes hangs
  • SF bug #448351: select.select() puts FDs on the heap where needed.

What's New in Python 2.1.1 (final) ?

  • The following bugs were fixed:
    • [ #441664 ] Python crash on del of a slice of a mmap
    • [ #438050 ] configure doesn't look for poll.h in sys
    • [ #437487 ] 2.1 build on Solaris fails if CC is set
    • [ #441527 ] unixccompiler preprocessor broken

What's New in Python 2.1.1c1 ?

  • Python 2.1.1 comes with the new, GPL-compatible PSF licence.
  • Several insecurities in dict comparison as well as a scoping bug, that could lead to the Python interpreter crashing were fixed.
  • Python should compile and run out of the box using the Borland C compiler (under Windows), thanks to Stephen Hansen.
  • A large number of bugs was fixed, both in code and in the documentation, including (but not limited to) the following bugreports from SourceForge:
    • [ #416530 ] No notes for building on Mac OS X 10.0
    • [ #416573 ] makesockaddr() AF_UNIX ignores sun_len
    • [ #417030 ] print '%*s' fails for unicode string
    • [ #417093 ] Case sensitive import: dir and .py file w/ same name
    • [ #417418 ] Python 2.1 compile error on HPUX
    • [ #417587 ] compiler warnings compiling 2.1
    • [ #417845 ] Python 2.1: SocketServer.ThreadingMixIn
    • [ #417943 ] xreadlines documented twice for file obj
    • [ #418296 ] WinMain.c should use WIN32_LEAN_AND_MEAN.
    • [ #418615 ] regular expression bug in pipes.py.
    • [ #418977 ] Access Violation in PyCell_Set
    • [ #419434 ] Tutorial contains wrong sample code.
    • [ #419873 ] ThreadingTCPServer invalidating sockets
    • [ #420216 ] bad links in v2.1 docs
    • [ #420230 ] fileinput deletes backups without warnin
    • [ #420343 ] SystemError from tuple() builtin
    • [ #420399 ] wrong HTML ("trademark" symbols?)
    • [ #421999 ] wrong priority doc for ** vs unary -
    • [ #422108 ] Error in rich comparisons
    • [ #422121 ] Insecurities in dict comparison
    • [ #422702 ] dbhash.open default
    • [ #423087 ] A small typo in weakref documentation
    • [ #423429 ] very minor nit in library ref
    • [ #424776 ] SMTP Example does not work
    • [ #424951 ] ThreadingTCPServer file handle errors.
    • [ #425320 ] Typo in introduction.
    • [ #427698 ] objects with __eq__ are not hashable
    • [ #427783 ] Lang Ref section 4.1 s/is/in/
    • [ #427985 ] optional "listen" parameter in asyncore
    • [ #428419 ] include/rangeobject.h needs extern "C"
    • [ #429059 ] No docs for os.getenv()
    • [ #429070 ] Thread.getDaemon()should be isDaemon()
    • [ #429361 ] popen2.Popen3.wait() exit code
    • [ #429554 ] PyList_SET_ITEM documentation omission
    • [ #430627 ] Fixes for templates/module.tex file
    • [ #430991 ] wrong co_lnotab
    • [ #431772 ] traceback.print_exc() causes traceback
    • [ #432369 ] ConfigParser: problem w/ mixed-case opts
    • [ #433228 ] repr(list) woes when len(list) big
    • [ #433904 ] rexec: all s_* methods return None only
    • [ #434186 ] 0x80000000/2 != 0x80000000>>1
    • [ #434975 ] Typo on Posix Large File Support page
    • [ #435066 ] PyObject_ClearWeakRefs misdocumented
    • [ #436525 ] Wrong macro name
    • [ #437041 ] strfime %Z isn't an RFC 822 timezone
    • [ #437879 ] SocketServer.py related problems
    • [ #438032 ] Documentation errors in module "profile"
    • [ #439012 ] Need doc: initial state of allocs
    • [ #439104 ] Tuple richcompares has code-typo
    • [ #439798 ] Nested scopes core dump
    • [ #439823 ] poll docs should mention timeout unit
    • [ #440037 ] C API descriptions not complete/consistent

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:

    1. If the PYTHONCASEOK environment variable exists, same as before: silently accept the first case-insensitive match of any kind; raise ImportError if none found.
    2. 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 PCbuildreadme.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]) issues a warning message; this can also be called from C as PyErr_Warn(category, message).

  • A new module xreadlines was added. This exports a single factory function, xreadlines(). The intention is that this code is the absolutely fastest way to iterate over all lines in an open file(-like) object:

    import xreadlines
for line in xreadlines.xreadlines(file):
    ...do something to line...

This is equivalent to the previous the speed record holder using
file.readlines(sizehint).  Note that if file is a real file object
(as opposed to a file-like object), this is equivalent:

for line in file.xreadlines():
    ...do something to line...

  • The bisect module has new functions bisect_left, insort_left, bisect_right and insort_right. The old names bisect and insort are now aliases for bisect_right and insort_right. XXX_right and XXX_left methods differ in what happens when the new element compares equal to one or more elements already in the list: the XXX_left methods insert to the left, the XXX_right methods to the right. Code that doesn't care where equal elements end up should continue to use the old, short names ("bisect" and "insort").

  • The new curses.panel module wraps the panel library that forms part of SYSV curses and ncurses. Contributed by Thomas Gellekum.

  • The SocketServer module now sets the allow_reuse_address flag by default in the TCPServer class.

  • A new function, sys._getframe(), returns the stack frame pointer of the caller. This is intended only as a building block for higher-level mechanisms such as string interpolation.

  • The pyexpat module supports a number of new handlers, which are available only in expat 1.2. If invocation of a callback fails, it will report an additional frame in the traceback. Parser objects participate now in garbage collection. If expat reports an unknown encoding, pyexpat will try to use a Python codec; that works only for single-byte charsets. The parser type objects is exposed as XMLParserObject.

  • xml.dom now offers standard definitions for symbolic node type and exception code constants, and a hierarchy of DOM exceptions. minidom was adjusted to use them.

  • The conformance of xml.dom.minidom to the DOM specification was improved. It detects a number of additional error cases; the previous/next relationship works even when the tree is modified; Node supports the normalize() method; NamedNodeMap, DocumentType and DOMImplementation classes were added; Element supports the hasAttribute and hasAttributeNS methods; and Text supports the splitText method.

Build issues

  • For Unix (and Unix-compatible) builds, configuration and building of extension modules is now greatly automated. Rather than having to edit the Modules/Setup file to indicate which modules should be built and where their include files and libraries are, a distutils-based setup.py script now takes care of building most extension modules. All extension modules built this way are built as shared libraries. Only a few modules that must be linked statically are still listed in the Setup file; you won't need to edit their configuration.
  • Python should now build out of the box on Cygwin. If it doesn't, mail to Jason Tishler (jlt63 at users.sourceforge.net).
  • Python now always uses its own (renamed) implementation of getopt() -- there's too much variation among C library getopt() implementations.
  • C++ compilers are better supported; the CXX macro is always set to a C++ compiler if one is found.

Windows changes

  • select module: By default under Windows, a select() call can specify no more than 64 sockets. Python now boosts this Microsoft default to 512. If you need even more than that, see the MS docs (you'll need to #define FD_SETSIZE and recompile Python from source).
  • Support for Windows 3.1, DOS and OS/2 is gone. The Lib/dos-8x3 subdirectory is no more!