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What's New In Python 3.0

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What's New in Python 3.0 final

Release date: 03-Dec-2008

Core and Builtins

  • Issue #3996: On Windows, the PyOS_CheckStack function would cause the interpreter to abort ("Fatal Python error: Could not reset the stack!") instead of throwing a MemoryError.
  • Issue #3689: The list reversed iterator now supports __length_hint__ instead of __len__. Behavior now matches other reversed iterators.
  • Issue #4367: Python would segfault during compiling when the unicodedata module couldn't be imported and N escapes were present.
  • Fix build failure of _cursesmodule.c building with -D_FORTIFY_SOURCE=2.


  • Issue #4387: binascii now refuses to accept str as binary input.
  • Issue #4073: Add 2to3 support to build_scripts, refactor that support in build_py.
  • IDLE would print a "Unhandled server exception!" message when internal debugging is enabled.
  • Issue #4455: IDLE failed to display the windows list when two windows have the same title.
  • Issue #3741: DISTUTILS_USE_SDK set causes to raise an exception.
  • Issue #4433: Fixed an access violation when garbage collecting _ctypes.COMError instances.
  • Issue #4429: Fixed UnicodeDecodeError in ctypes.
  • Issue #4373: Corrected a potential reference leak in the pickle module and silenced a false positive ref leak in distutils.tests.test_build_ext.
  • Issue #4382: dbm.dumb did not specify the expected file encoding for opened files.
  • Issue #4383: When IDLE cannot make the connection to its subprocess, it would fail to properly display the error message.


  • Issue #4407: Fix source file that caused the compileall step in Windows installer to fail.


  • Issue #4449: Fixed multiprocessing examples
  • Issue #3799: Document that dbm.gnu and dbm.ndbm will accept string arguments for keys and values which will be converted to bytes before committal.

What's New in Python 3.0 release candidate 3?

Release date: 20-Nov-2008

Core and Builtins

  • Issue #4349: sys.path included a non-existent platform directory because of a faulty Makefile.
  • Issue #3327: Don't overallocate in the modules_by_index list.
  • Issue #1721812: Binary set operations and copy() returned the input type instead of the appropriate base type. This was incorrect because set subclasses would be created without their __init__() method being called. The corrected behavior brings sets into line with lists and dicts.
  • Issue #4296: Fix PyObject_RichCompareBool so that "x in [x]" evaluates to True, even when x doesn't compare equal to itself. This was a regression from 2.6.
  • Issue #3705: Command-line arguments were not correctly decoded when the terminal does not use UTF8.


  • Issue #4363: The uuid.uuid1() and uuid.uuid4() functions now work even if the ctypes module is not present.
  • FileIO's mode attribute now always includes "b".
  • Issue #3799: Fix dbm.dumb to accept strings as well as bytes for keys. String keys are now written out in UTF-8.
  • Issue #4338: Fix distutils upload command.
  • Issue #4354: Fix distutils register command.
  • Issue #4116: Resolve member name conflict in ScrolledCanvas.__init__.
  • Issue #4307: The named tuple that inspect.getfullargspec() returns now uses kwonlydefaults instead of kwdefaults.
  • Issue #4298: Fix a segfault when pickle.loads is passed a ill-formed input.
  • Issue #4283: Fix a left-over "iteritems" call in distutils.


  • Issue #4389: Add icon to the uninstall entry in "add-and-remove-programs".
  • Issue #4289: Remove Cancel button from AdvancedDlg.
  • Issue #1656675: Register a drop handler for .py* files on Windows.


  • Demos of the socketserver module now work with Python 3.

What's New in Python 3.0 release candidate 2

Release date: 05-Nov-2008

Core and Builtins

  • Issue #4211: The __path__ attribute of frozen packages is now a list instead of a string as required by PEP 302.
  • Issue #3727: Fixed poplib.
  • Issue #3714: Fixed nntplib by using bytes where appropriate.
  • Issue #1210: Fixed imaplib and its documentation.
  • Issue #4233: Changed semantic of _fileio.FileIO's close() method on file objects with closefd=False. The file descriptor is still kept open but the file object behaves like a closed file. The FileIO object also got a new readonly attribute closefd.
  • Issue #3626: On cygwin, starting python with a non-existent script name would not display anything if the file name is only 1 character long.
  • Issue #4176: Fixed a crash when pickling an object which __reduce__ method does not return iterators for the 4th and 5th items.
  • Issue #3723: Fixed initialization of subinterpreters.
  • Issue #4213: The file system encoding is now normalized by the codec subsystem, for example UTF-8 is turned into utf-8.
  • Issue #4200: Changed the atexit module to store its state in its PyModuleDef atexitmodule. This fixes a bug with multiple subinterpeters.
  • Issue #4237: io.FileIO() was raising invalid warnings caused by insufficient initialization of PyFileIOObject struct members.
  • Issue #4170: Pickling a collections.defaultdict object would crash the interpreter.
  • Issue #4146: Compilation on OpenBSD has been restored.
  • Issue #3574: compile() incorrectly handled source code encoded as Latin-1.
  • Issues #2384 and #3975: Tracebacks were not correctly printed when the source file contains a coding: header: the wrong line was displayed, and the encoding was not respected.
  • Issue #3740: Null-initialize module state.
  • Issue #3946: PyObject_CheckReadBuffer crashed on a memoryview object.
  • Issue #1688: On Windows, the input() prompt was not correctly displayed if it contains non-ascii characters.
  • Bug #3951: Py_USING_MEMORY_DEBUGGER should not be enabled by default.


  • Issue #3664: The pickle module could segfault if a subclass of Pickler fails to call the base __init__ method.
  • Issue #3725: telnetlib now works completely in bytes.
  • Issue #4072: Restore build_py_2to3.
  • Issue #4014: Don't claim that Python has an Alpha release status, in addition to claiming it is Mature.
  • Issue #3187: Add sys.setfilesystemencoding.
  • Issue #3187: Better support for "undecodable" filenames. Code by Victor Stinner, with small tweaks by GvR.
  • Issue #3965: Allow repeated calls to turtle.Screen, by making it a true singleton object.
  • Issue #3911: ftplib.FTP.makeport() could give invalid port numbers.
  • Issue #3929: When the database cannot be opened, would incorrectly raise a TypeError: "'tuple' object is not callable" instead of the expected dbm.error.
  • Bug #3884: Make the turtle module toplevel again.
  • Issue #3547: Fixed ctypes structures bitfields of varying integer sizes.

Extension Modules

  • Issue #3659: Subclasses of str didn't work as SQL parameters.


  • Issue #4120: Exclude manifest from extension modules in VS2008.
  • Issue #4091: Install pythonxy.dll in system32 again.
  • Issue #4018: Disable "for me" installations on Vista.
  • Issue #4204: Fixed module build errors on FreeBSD 4.


  • Issue #3717: Fix Demo/embed/demo.c.
  • Issue #4072: Add a distutils demo for build_py_2to3.

What's New in Python 3.0 release candidate 1

Release date: 17-Sep-2008

Core and Builtins

  • Issue #3827: memoryview lost its size attribute in favor of using len(view).
  • Issue #3813: could not lanch python.exe via symbolic link on cygwin.
  • Issue #3705: fix crash when given a non-ascii value on the command line for the "-c" and "-m" parameters. Now the behaviour is as expected under Linux, although under Windows it fails at a later point.
  • Issue #3279: Importing site at interpreter was failing silently because the site module uses the open builtin which was not initialized at the time.
  • Issue #3660: Corrected a reference leak in str.encode() when the encoder does not return a bytes object.
  • Issue #3774: Added a few more checks in PyTokenizer_FindEncoding to handle error conditions.
  • Issue #3594: Fix Parser/tokenizer.c:fp_setreadl() to open the file being tokenized by either a file path or file pointer for the benefit of PyTokenizer_FindEncoding().
  • Issue #3696: Error parsing arguments on OpenBSD <= 4.4 and Cygwin. On these systems, the mbstowcs() function is slightly buggy and must be replaced with strlen() for the purpose of counting of number of wide characters needed to represent the multi-byte character string.
  • Issue #3697: "Fatal Python error: Cannot recover from stack overflow" could be easily encountered under Windows in debug mode when exercising the recursion limit checking code, due to bogus handling of recursion limit when USE_STACKCHEK was enabled.
  • Issue 3639: The _warnings module could segfault the interpreter when unexpected types were passed in as arguments.
  • Issue #3712: The memoryview object had a reference leak and didn't support cyclic garbage collection.
  • Issue #3668: Fix a memory leak with the "s*" argument parser in PyArg_ParseTuple and friends, which occurred when the argument for "s*" was correctly parsed but parsing of subsequent arguments failed.
  • Issue #3611: An exception __context__ could be cleared in a complex pattern involving a __del__ method re-raising an exception.
  • Issue #2534: speed up isinstance() and issubclass() by 50-70%, so as to match Python 2.5 speed despite the __instancecheck__ / __subclasscheck__ mechanism. In the process, fix a bug where isinstance() and issubclass(), when given a tuple of classes as second argument, were looking up __instancecheck__ / __subclasscheck__ on the tuple rather than on each type object.
  • Issue #3663: Py_None was decref'd when printing SyntaxErrors.
  • Issue #3651: Fix various memory leaks when using the buffer interface, or when the "s#" code of PyArg_ParseTuple is given a bytes object.
  • Issue #3657: Fix uninitialized memory read when pickling longs. Found by valgrind.
  • Apply security patches from Apple.
  • Fix crashes on memory allocation failure found with failmalloc.
  • Fix memory leaks found with valgrind and update suppressions file.
  • Fix compiler warnings in opt mode which would lead to invalid memory reads.
  • Fix problem using wrong name in decimal module reported by pychecker.
  • Issue #3650: Fixed a reference leak in bytes.split('x').
  • bytes(o) now tries to use o.__bytes__() before using fallbacks.
  • Issue #1204: The configure script now tests for additional libraries that may be required when linking against readline. This fixes issues with x86_64 builds on some platforms (a few Linux flavors and OpenBSD).


  • PyObject_Bytes and PyBytes_FromObject were added.


  • Issue #3756: make re.escape() handle bytes as well as str.
  • Issue #3800: fix filter() related bug in
  • Issue #874900: fix behaviour of threading module after a fork.
  • Issue #3535: zipfile couldn't read some zip files larger than 2GB.
  • Issue #3776: Deprecate the bsddb package for removal in 3.0.
  • Issue #3762: platform.architecture() fails if python is lanched via its symbolic link.
  • Issue #3660: fix a memory leak in the C accelerator of the pickle module.
  • Issue #3160: the "bdist_wininst" distutils command didn't work.
  • Issue #1658: tkinter changes dict size during iteration in both tkinter.BaseWidget and tkinter.scrolledtext.ScrolledText.
  • The bsddb module (and therefore the dbm.bsd module) has been removed. It is now maintained outside of the standard library at
  • Issue 600362: Relocated parse_qs() and parse_qsl(), from the cgi module to the urlparse one. Added a DeprecationWarning in the old module, it will be deprecated in the future.
  • Issue #3719: platform.architecture() fails if there are spaces in the path to the Python binary.
  • Issue 3602: As part of the merge of r66135, make the parameters on warnings.catch_warnings() keyword-only. Also remove a DeprecationWarning.
  • The deprecation warnings for the camelCase threading API names were removed.
  • Issue #3110: multiprocessing fails to compiel on solaris 10 due to missing SEM_VALUE_MAX.

Extension Modules

  • Issue #3782: os.write() must not accept unicode strings.
  • Issue #2975: When compiling several extension modules with Visual Studio 2008 from the same python interpreter, some environment variables would grow without limit.
  • Issue #3643: Added a few more checks to _testcapi to prevent segfaults by exploitation of poor argument checking.
  • bsddb code updated to version 4.7.3pre2. This code is the same than Python 2.6 one, since the intention is to keep an unified 2.x/3.x codebase. The Python code is automatically translated using "2to3". Please, do not update this code in Python 3.0 by hand. Update the 2.6 one and then do "2to3".
  • The _bytesio and _stringio modules are now compiled into the python binary.
  • Issue #3492 and #3790: Fixed the zlib module and zipimport module uses of mutable bytearray objects where they should have been using immutable bytes.
  • Issue #3797: Fixed the dbm, marshal, mmap, ossaudiodev, & winreg modules to return bytes objects instead of bytearray objects.


  • Fix Misc/gdbinit so it works.


  • Issue #3812: Failed to build python if configure --without-threads.
  • Issue #3791: Remove the bsddb module from the Windows installer, and the core bsddb library from the Windows build files.

What's new in Python 3.0b3?

Release date: 20-Aug-2008

Core and Builtins

  • Issue #3653: Fix a segfault when sys.excepthook was called with invalid arguments.

  • Issue #2394: implement more of the memoryview API, with the caveat that only one-dimensional contiguous buffers are supported and exercised right now. Slicing, slice assignment and comparison (equality and inequality) have been added. Also, the tolist() method has been implemented, but only for byte buffers. Endly, the API has been updated to return bytes objects wherever it used to return bytearrays.

  • Issue #3560: clean up the new C PyMemoryView API so that naming is internally consistent; add macros PyMemoryView_GET_BASE() and PyMemoryView_GET_BUFFER() to access useful properties of a memory views without relying on a particular implementation; remove the ill-named PyMemoryView() function (PyMemoryView_GET_BUFFER() can be used instead).

  • ctypes function pointers that are COM methods have a boolean True value again.

  • Issue #1819: function calls with several named parameters are now on average 35% faster (as measured by pybench).

  • The undocumented C APIs PyUnicode_AsString() and PyUnicode_AsStringAndSize() were made private to the interpreter, in order to be able to refine their interfaces for Python 3.1.

    If you need to access the UTF-8 representation of a Unicode object as bytes string, please use PyUnicode_AsUTF8String() instead.

  • Issue #3460: PyUnicode_Join() implementation is 10% to 80% faster thanks to Python 3.0's stricter semantics which allow to avoid successive reallocations of the result string (this also affects str.join()).


  • Issue #1276: Added temporary aliases for CJK Mac encodings to resolve a build problem on MacOS with CJK locales. It adds four temporary mappings to existing legacy codecs that are virtually compatible with Mac encodings. They will be replaced by codecs correctly implemented in 3.1.
  • Issue #3614: Corrected a typo in xmlrpc.client, leading to a NameError "global name 'header' is not defined".
  • Issue #2834: update the regular expression library to match the unicode standards of py3k. In other words, mixing bytes and unicode strings (be it as pattern, search string or replacement string) raises a TypeError. Moreover, the re.UNICODE flag is enabled automatically for unicode patterns, and can be disabled by specifying a new re.ASCII flag; as for bytes patterns, ASCII matching is the only option and trying to specify re.UNICODE for such patterns raises a ValueError.
  • Issue #3300: make urllib.parse.[un]quote() default to UTF-8. Code contributed by Matt Giuca. quote() now encodes the input before quoting, unquote() decodes after unquoting. There are new arguments to change the encoding and errors settings. There are also new APIs to skip the encode/decode steps. [un]quote_plus() are also affected.
  • Issue #2235: numbers.Number now blocks inheritance of the default id() based hash because that hash mechanism is not correct for numeric types. All concrete numeric types that inherit from Number (rather than just registering with it) must explicitly provide a hash implementation in order for their instances to be hashable.
  • Issue #2676: in the email package, content-type parsing was hanging on pathological input because of quadratic or exponential behaviour of a regular expression.
  • Issue #3476: binary buffered reading through the new "io" library is now thread-safe.
  • Issue #1342811: Fix leak in Tkinter.Menu.delete. Commands associated to menu entries were not deleted.
  • Remove the TarFileCompat class from
  • Issue #2491: os.fdopen is now almost an alias for the built-in open(), and accepts the same parameters. It just checks that its first argument is an integer.
  • Issue #3394: zipfile.writestr sets external attributes when passed a file name rather than a ZipInfo instance, so files are extracted with mode 0600 rather than 000 under Unix.
  • Issue #2523: Fix quadratic behaviour when read()ing a binary file without asking for a specific length.

Extension Modules

  • Bug #3542: Support Unicode strings in _msi module.

What's new in Python 3.0b2?

Release date: 17-Jul-2008

Core and Builtins

  • Issue #3008: the float type has a new instance method 'float.hex' and a new class method 'float.fromhex' to convert floating-point numbers to and from hexadecimal strings, respectively.
  • Issue #3083: Add alternate (#) formatting for bin, oct, hex output for str.format(). This adds the prefix 0b, 0o, or 0x, respectively.
  • Issue #3280: like chr(), the "%c" format now accepts unicode code points beyond the Basic Multilingual Plane (above 0xffff) on all configurations. On "narrow Unicode" builds, the result is a string of 2 code units, forming a UTF-16 surrogate pair.
  • Issue #3282: str.isprintable() should return False for undefined Unicode characters.
  • Issue #3236: Return small longs from PyLong_FromString.
  • Exception tracebacks now support exception chaining.


  • Removed the sunaudio module. Use sunau instead.
  • Issue #3554: ctypes.string_at and ctypes.wstring_at did call Python api functions without holding the GIL, which could lead to a fatal error when they failed.
  • Issue #799428: Fix Tkinter.Misc._nametowidget to unwrap Tcl command objects.
  • Removed "ast" function aliases from the parser module.
  • Issue #3313: Fixed a crash when a failed dlopen() call does not set a valid dlerror() message.
  • Issue #3258: Fixed a crash when a ctypes POINTER type to an incomplete structure was created.
  • Issue #2683: Fix inconsistency in subprocess.Popen.communicate(): the argument now must be a bytes object in any case.
  • Issue #3145: help("modules whatever") failed when trying to load the source code of every single module of the standard library, including invalid files used in the test suite.
  • The gettext library now consistently uses Unicode strings for message ids and message strings, and ugettext() and the like don't exist anymore.
  • The traceback module has been expanded to handle chained exceptions.


  • Issue #3247: the function Py_FindMethod was removed. Modern types should use the tp_methods slot instead.


  • The Mac/Demos directory has been removed.
  • All of the Mac scripts have been removed (including

What's new in Python 3.0b1?

Release date: 18-Jun-2008

Core and Builtins

  • Issue #3211: warnings.warn_explicit() did not guard against its 'registry' argument being anything other than a dict or None. Also fixed a bug in error handling when 'message' and 'category' were both set to None, triggering a bus error.
  • Issue #3100: Corrected a crash on deallocation of a subclassed weakref which holds the last (strong) reference to its referent.
  • Issue #2630: implement PEP 3138. repr() now returns printable Unicode characters unescaped, to get an ASCII-only representation of an object use ascii().
  • Issue #1342: On windows, Python could not start when installed in a directory with non-ascii characters.
  • Implement PEP 3121: new module initialization and finalization API.
  • Removed the already-defunct -t option.
  • Issue #2957: Corrected a ValueError "recursion limit exceeded", when unmarshalling many code objects, which happens when importing a large .pyc file (~1000 functions).
  • Issue #2963: fix merging oversight that disabled method cache for all types.
  • Issue #2964: fix a missing INCREF in instancemethod_descr_get.
  • Issue #2895: Don't crash when given bytes objects as keyword names.
  • Issue #2798: When parsing arguments with PyArg_ParseTuple, the "s" code now allows any unicode string and returns a utf-8 encoded buffer, just like the "s#" code already does. The "z" code was corrected as well.
  • Issue #2863: generators now have a gen.__name__ attribute that equals gen.gi_code.co_name, like func.__name___ that equals func.func_code.co_name. The repr() of a generator now also contains this name.
  • Issue #2831: enumerate() now has a start argument.
  • Issue #2801: fix bug in the float.is_integer method where a ValueError was sometimes incorrectly raised.
  • The --with-toolbox-glue option (and the associated pymactoolbox.h) have been removed.
  • Issue #2196: hasattr() now lets exceptions which do not inherit Exception (KeyboardInterrupt, and SystemExit) propagate instead of ignoring them.
  • #3021 Exception reraising sematics have been significantly improved. However, f_exc_type, f_exc_value, and f_exc_traceback cannot be accessed from Python code anymore.
  • Three of PyNumberMethods' members, nb_coerce, nb_hex, and nb_oct, have been removed.

Extension Modules

  • Renamed _winreg module to winreg.
  • Support os.O_ASYNC and fcntl.FASYNC if the constants exist on the platform.
  • Support for Windows 9x has been removed from the winsound module.
  • Issue #2870: cmathmodule.c compile error.


  • The methods is_in_tuple(), is_vararg(), and is_keywordarg() of symtable.Symbol have been removed.
  • Patch #3133: http.server.CGIHTTPRequestHandler did not work on windows.
  • a new urllib package was created. It consists of code from urllib, urllib2, urlparse, and robotparser. The old modules have all been removed. The new package has five submodules: urllib.parse, urllib.request, urllib.response, urllib.error, and urllib.robotparser. The urllib.request.urlopen() function uses the url opener from urllib2. (Note that the unittests have not been renamed for the beta, but they will be renamed in the future.)
  • rfc822 has been removed in favor of the email package.
  • mimetools has been removed in favor of the email package.
  • Patch #2849: Remove use of rfc822 module from standard library.
  • Added C optimized implementation of io.StringIO.
  • The pickle module is now automatically use an optimized C implementation of Pickler and Unpickler when available. The cPickle module is no longer needed.
  • Removed the htmllib and sgmllib modules.
  • The deprecated SmartCookie and SimpleCookie classes have been removed from http.cookies.
  • The commands module has been removed. Its getoutput() and getstatusoutput() functions have been moved to the subprocess module.
  • The http package was created; it contains the old httplib as http.client, Cookie as http.cookies, cookielib as http.cookiejar, and the content of the three HTTPServer modules as http.server.
  • The xmlrpc package was created; it contains the old xmlrpclib module as xmlrpc.client and the content of the old SimpleXMLRPCServer and DocXMLRPCServer modules as xmlrpc.server.
  • The dbm package was created, containing the old modules anydbm and whichdb in its, and having dbm.gnu (was gdbm), dbm.bsd (was dbhash), dbm.ndbm (was dbm) and dbm.dumb (was dumbdbm) as submodules.
  • The repr module has been renamed to reprlib.
  • The statvfs module has been removed.
  • Issue #1713041: fix pprint's handling of maximum depth.
  • Issue #2250: Exceptions raised during evaluation of names in rlcompleter's Completer.complete() method are now caught and ignored.
  • Patch #2659: Added break_on_hyphens option to textwrap's TextWrapper class.
  • Issue #2487: change the semantics of math.ldexp(x, n) when n is too large to fit in a C long. ldexp(x, n) now returns a zero (with suitable sign) if n is large and negative; previously, it raised OverflowError.
  • The ConfigParser module has been renamed to configparser.
  • Issue #2865: works again in a KDE environment.
  • The multifile module has been removed.
  • The SocketServer module has been renamed to socketserver.
  • Fixed the __all__ setting on collections to include UserList and UserString.
  • The sre module has been removed.
  • The Queue module has been renamed to queue.
  • The copy_reg module has been renamed to copyreg.
  • The mhlib module has been removed.
  • The ihooks module has been removed.
  • The fpformat module has been removed.
  • The dircache module has been removed.
  • The Canvas module has been removed.
  • The Decimal module gained the magic methods __round__, __ceil__, __floor__ and __trunc__, to give support for round, math.ceil, math.floor and math.trunc.
  • The user module has been removed.
  • The mutex module has been removed.
  • The imputil module has been removed.
  • os.path.walk has been removed in favor of os.walk.
  • pdb gained the "until" command.
  • The test.test_support module has been renamed to
  • The threading module API was renamed to be PEP 8 compliant. The old names are still present, but will be removed in the near future.


  • The bgen tool has been removed.


What's New in Python 3.0a5?

Release date: 08-May-2008

Core and Builtins

  • Fixed misbehaviour of PyLong_FromSsize_t on systems where sizeof(size_t) > sizeof(long).
  • Issue #2221: Corrected a SystemError "error return without exception set", when the code executed by exec() raises an exception, and sys.stdout.flush() also raises an error.
  • Bug #2565: The repr() of type objects now calls them 'class', not 'type' - whether they are builtin types or not.
  • The command line processing was converted to pass Unicode strings through as unmodified as possible; as a consequence, the C API related to command line arguments was changed to use wchar_t.
  • All backslashes in raw strings are interpreted literally. This means that 'u' and 'U' escapes are not treated specially.

Extension Modules


  • ctypes objects now support the PEP3118 buffer interface.
  • Issue #2682: ctypes callback functions now longer contain a cyclic reference to themselves.
  • Issue #2058: Remove the buf attribute and add __slots__ to the TarInfo class in order to reduce tarfile's memory usage.
  • Bug #2606: Avoid calling .sort() on a dict_keys object.
  • The bundled libffi copy is now in sync with the recently released libffi3.0.5 version, apart from some small changes to Modules/_ctypes/libffi/


  • Issue #1496032: On alpha, use -mieee when gcc is the compiler.
  • "make install" is now an alias for "make altinstall", to prevent accidentally overwriting a Python 2.x installation. Use "make fullinstall" to force Python 3.0 to be installed as "python".
  • Issue #2544: On HP-UX systems, use 'gcc -shared' for linking when gcc is used as compiler.

What's New in Python 3.0a4?

Release date: 02-Apr-2008

Core and Builtins

  • Bug #2301: Don't try decoding the source code into the original encoding for syntax errors.

Extension Modules

  • The dl module was removed, use the ctypes module instead.
  • Use wchar_t functions in _locale module.


  • The class distutils.commands.build_py.build_py_2to3 can be used as a build_py replacement to automatically run 2to3 on modules that are going to be installed.
  • A new pickle protocol (protocol 3) is added with explicit support for bytes. This is the default protocol. It intentionally cannot be unpickled by Python 2.x.
  • When a pickle written by Python 2.x contains an (8-bit) str instance, this is now decoded to a (Unicode) str instance. The encoding used to do this defaults to ASCII, but can be overridden via two new keyword arguments to the Unpickler class. Previously this would create bytes instances, which is usually wrong: str instances are often used to pickle attribute names etc., and text is more common than binary data anyway.
  • Default to ASCII as the locale.getpreferredencoding, if the POSIX system doesn't support CODESET and LANG isn't set or doesn't allow deduction of an encoding.
  • Issue #1202: zlib.crc32 and zlib.adler32 now return an unsigned value.
  • Issue #719888: Updated tokenize to use a bytes API. generate_tokens has been renamed tokenize and now works with bytes rather than strings. A new detect_encoding function has been added for determining source file encoding according to PEP-0263. Token sequences returned by tokenize always start with an ENCODING token which specifies the encoding used to decode the file. This token is used to encode the output of untokenize back to bytes.

What's New in Python 3.0a3?

Release date: 29-Feb-2008

Core and Builtins

  • Issue #2282: io.TextIOWrapper was not overriding seekable() from io.IOBase.
  • Issue #2115: Important speedup in setting __slot__ attributes. Also prevent a possible crash: an Abstract Base Class would try to access a slot on a registered virtual subclass.
  • Fixed repr() and str() of complex numbers with infinity or nan as real or imaginary part.
  • Clear all free list during a gc.collect() of the highest generation in order to allow pymalloc to free more arenas. Python may give back memory to the OS earlier.
  • Issue #2045: Fix an infinite recursion triggered when printing a subclass of collections.defaultdict, if its default_factory is set to a bound method.
  • Fixed a minor memory leak in dictobject.c. The content of the free list was not freed on interpreter shutdown.
  • Limit free list of method and builtin function objects to 256 entries each.
  • Patch #1953: Added sys._compact_freelists() and the C API functions PyInt_CompactFreeList and PyFloat_CompactFreeList to compact the internal free lists of pre-allocted ints and floats.
  • Bug #1983: Fixed return type of fork(), fork1() and forkpty() calls. Python expected the return type int but the fork familie returns pi_t.
  • Issue #1678380: Fix a bug that identifies 0j and -0j when they appear in the same code unit.
  • Issue #2025: Added tuple.count() and tuple.index() methods to comply with the collections.Sequence API.
  • Fixed multiple reinitialization of the Python interpreter. The small int list in longobject.c has caused a seg fault during the third finalization.
  • Issue #1973: bytes.fromhex('') raised SystemError.
  • Issue #1771: remove cmp parameter from sorted() and list.sort().
  • Issue #1969: split and rsplit in bytearray are inconsistent.
  • map() no longer accepts None for the first argument. Use zip() instead.
  • Issue #1769: Now int("- 1") is not allowed any more.
  • Object/longobject.c: long(float('nan')) raises an OverflowError instead of returning 0.
  • Issue #1762972: __file__ points to the source file instead of the pyc/pyo file if the py file exists.
  • Issue #1393: object_richcompare() returns NotImplemented instead of False if the objects aren't equal, to give the other side a chance.
  • Issue #1692: Interpreter was not displaying location of SyntaxError.
  • Improve some exception messages when Windows fails to load an extension module. Now we get for example '%1 is not a valid Win32 application' instead of 'error code 193'. Also use Unicode strings to deal with non-English locales.
  • Issue #1587: Added instancemethod wrapper for PyCFunctions. The Python C API has gained a new type PyInstanceMethod_Type and the functions PyInstanceMethod_Check(o), PyInstanceMethod_New(func) and PyInstanceMethod_Function(im).
  • Constants gc.DEBUG_OBJECT and gc.DEBUG_INSTANCE have been removed from the gc module; gc.DEBUG_COLLECTABLE or gc.DEBUG_UNCOLLECTABLE are now enough to print the corresponding list of objects considered by the garbage collector.
  • Issue #1573: Improper use of the keyword-only syntax makes the parser crash.
  • Issue #1564: The set implementation should special-case PyUnicode instead of PyString.
  • Patch #1031213: Decode source line in SyntaxErrors back to its original source encoding.
  • inspect.getsource() includes the decorators again.
  • Bug #1713: posixpath.ismount() claims symlink to a mountpoint is a mountpoint.
  • Fix utf-8-sig incremental decoder, which didn't recognise a BOM when the first chunk fed to the decoder started with a BOM, but was longer than 3 bytes.

Extension Modules

  • Code for itertools ifilter(), imap(), and izip() moved to bultins and renamed to filter(), map(), and zip(). Also, renamed izip_longest() to zip_longest() and ifilterfalse() to filterfalse().
  • Issue #1762972: Readded the reload() function as imp.reload().
  • Bug #2111: mmap segfaults when trying to write a block opened with PROT_READ.
  • Issue #2063: correct order of utime and stime in os.times() result on Windows.


  • Weakref dictionaries now inherit from MutableMapping.
  • Created new UserDict class in collections module. This one inherits from and complies with the MutableMapping ABC. Also, moved UserString and UserList to the collections module. The MutableUserString class was removed.
  • Removed UserDict.DictMixin. Replaced all its uses with collections.MutableMapping.
  • Issue #1703: getpass() should flush after writing prompt.
  • Issue #1585: IDLE uses non-existent xrange() function.
  • Issue #1578: Problems in win_getpass.


  • Renamed --enable-unicode configure flag to --with-wide-unicode, since Unicode strings can't be disabled anymore.


  • Issue #1629: Renamed Py_Size, Py_Type and Py_Refcnt to Py_SIZE, Py_TYPE and Py_REFCNT.
  • New API PyImport_ImportModuleNoBlock(), works like PyImport_ImportModule() but won't block on the import lock (returning an error instead).

What's New in Python 3.0a2?

Release date: 07-Dec-2007

(Note: this list is incomplete.)

Core and Builtins

  • str8 now has the same construction signature as bytes.
  • Comparisons between str and str8 now return False/True for ==/!=. sqlite3 returns str8 when recreating on object from it's __conform__ value. The struct module returns str8 for all string-related formats. This was true before this change, but becomes more apparent thanks to string comparisons always being False.
  • Replaced PyFile_FromFile() with PyFile_FromFd(fd, name. mode, buffer, encoding, newline).
  • Fixed imp.find_module() to obey the -- coding: -- header.
  • Changed __file__ and co_filename to unicode. The path names are decoded with Py_FileSystemDefaultEncoding and a new API method PyUnicode_DecodeFSDefault(char*) was added.
  • and _fileio.FileIO have grown a new argument closefd. A false value disables the closing of the file descriptor.
  • Added a new option -b to issues warnings (-bb for errors) about certain operations between bytes/buffer and str like str(b'') and comparison.
  • The standards streams sys.stdin, stdout and stderr may be None when the when the C runtime library returns an invalid file descriptor for the streams (fileno(stdin) < 0). For now this happens only for Windows GUI apps and scripts started with pythonw.exe.
  • Added PCbuild9 directory for VS 2008.
  • Renamed structmember.h WRITE_RESTRICTED to PY_WRITE_RESTRICTED to work around a name clash with VS 2008 on Windows.
  • Unbound methods are gone for good. ClassObject.method returns an ordinary function object, instance.method still returns a bound method object. The API of bound methods is cleaned up, too. The im_class attribute is removed and im_func + im_self are renamed to __func__ and __self__. The factory PyMethod_New takes only func and instance as argument.
  • intobject.h is no longer included by Python.h. The remains were moved to longobject.h. It still exists to define several aliases from PyInt to PyLong functions.
  • Removed sys.maxint, use sys.maxsize instead.

Extension Modules

  • The hotshot profiler has been removed; use cProfile instead.


  • When loading an external file using testfile(), the passed-in encoding argument was being ignored if __loader__ is defined and forcing the source to be UTF-8.
  • The methods os.tmpnam(), os.tempnam() and os.tmpfile() have been removed in favor of the tempfile module.
  • Removed the 'new' module.
  • Removed all types from the 'types' module that are easily accessable through builtins.

What's New in Python 3.0a1?

Release date: 31-Aug-2007

Core and Builtins

  • PEP 3131: Support non-ASCII identifiers.

  • PEP 3120: Change default encoding to UTF-8.

  • PEP 3123: Use proper C inheritance for PyObject.

  • Removed the __oct__ and __hex__ special methods and added a bin() builtin function.

  • PEP 3127: octal literals now start with "0o". Old-style octal literals are invalid. There are binary literals with a prefix of "0b". This also affects int(x, 0).

  • None, True, False are now keywords.

  • PEP 3119: isinstance() and issubclass() can be overridden.

  • Remove BaseException.message.

  • Remove tuple parameter unpacking (PEP 3113).

  • Remove the f_restricted attribute from frames. This naturally leads to the removal of PyEval_GetRestricted() and PyFrame_IsRestricted().

  • PEP 3132 was accepted. That means that you can do a, *b = range(5) to assign 0 to a and [1, 2, 3, 4] to b.

  • range() now returns an iterator rather than a list. Floats are not allowed. xrange() is no longer defined.

  • Patch #1660500: hide iteration variable in list comps, add set comps and use common code to handle compilation of iterative expressions.

  • By default, != returns the opposite of ==, unless the latter returns NotImplemented.

  • Patch #1680961: sys.exitfunc has been removed and replaced with a private C-level API.

  • PEP 3115: new metaclasses: the metaclass is now specified as a keyword arg in the class statement, which can now use the full syntax of a parameter list. Also, the metaclass can implement a __prepare__ function which will be called to create the dictionary for the new class namespace.

  • The long-deprecated argument "pend" of PyFloat_FromString() has been removed.

  • The dir() function has been extended to call the __dir__() method on its argument, if it exists. If not, it will work like before. This allows customizing the output of dir() in the presence of a __getattr__().

  • Removed support for __members__ and __methods__.

  • Removed indexing/slicing on BaseException.

  • input() became raw_input(): the name input() now implements the functionality formerly known as raw_input(); the name raw_input() is no longer defined.

  • Classes listed in an 'except' clause must inherit from BaseException.

  • PEP 3106: dict.iterkeys(), .iteritems(), .itervalues() are now gone; and .keys(), .items(), .values() return dict views, which behave like sets.

  • PEP 3105: print is now a function. Also (not in the PEP) the 'softspace' attribute of files is now gone (since print() doesn't use it). A side effect of this change is that you can get incomplete output lines in interactive sessions:

    >>> print(42, end="")

    We may be able to fix this after the I/O library rewrite.

  • PEP 3102: keyword-only arguments.

  • Int/Long unification is complete. The 'long' built-in type and literals with trailing 'L' or 'l' have been removed. Performance may be sub-optimal (haven't really benchmarked).

  • 'except E, V' must now be spelled as 'except E as V' and deletes V at the end of the except clause; V must be a simple name.

  • Added function annotations per PEP 3107.

  • Added nonlocal declaration from PEP 3104:

    >>> def f(x):
    ...     def inc():
    ...         nonlocal x
    ...         x += 1
    ...         return x
    ...     return inc
    >>> inc = f(0)
    >>> inc()
    >>> inc()
  • Moved intern() to sys.intern().

  • exec is now a function.

  • Renamed nb_nonzero to nb_bool and __nonzero__ to __bool__.

  • Classic classes are a thing of the past. All classes are new style.

  • Exceptions must derive from BaseException.

  • Integer division always returns a float. The -Q option is no more. All the following are gone:

    • PyNumber_Divide and PyNumber_InPlaceDivide
    • __div__, __rdiv__, and __idiv__
    • nb_divide, nb_inplace_divide
    • operator.div, operator.idiv, operator.__div__, operator.__idiv__ (Only __truediv__ and __floordiv__ remain, not sure how to handle them if we want to re-use __div__ and friends. If we do, it will make it harder to write code for both 2.x and 3.x.)
  • 'as' and 'with' are keywords.

  • Absolute import is the default behavior for 'import foo' etc.

  • Removed support for syntax: backticks (ie, x), <>.

  • Removed these Python builtins: apply(), callable(), coerce(), execfile(), file(), reduce(), reload().

  • Removed these Python methods: {}.has_key.


  • Remove C API support for restricted execution.

  • zip(), map() and filter() now return iterators, behaving like their itertools counterparts. This also affect map()'s behavior on sequences of unequal length -- it now stops after the shortest one is exhausted.

  • Additions: set literals, set comprehensions, ellipsis literal.

  • Added class decorators per PEP 3129.

Extension Modules

  • Removed the imageop module. Obsolete long with its unit tests becoming useless from the removal of rgbimg and imgfile.
  • Removed these attributes from the operator module: div, idiv, __div__, __idiv__, isCallable, sequenceIncludes.
  • Removed these attributes from the sys module: exc_clear(), exc_type, exc_value, exc_traceback.


  • Removed the compiler package. Use of the _ast module and (an eventual) AST -> bytecode mechanism.
  • Removed these modules: audiodev, Bastion, bsddb185, exceptions, linuxaudiodev, md5, MimeWriter, mimify, popen2, rexec, sets, sha, stringold, strop, sunaudiodev, timing, xmllib.
  • Moved the toaiff module to Tools/Demos.
  • Removed obsolete IRIX modules: al/AL, cd/CD, cddb, cdplayer, cl/CL, DEVICE, ERRNO, FILE, fl/FL, flp, fm, GET, gl/GL, GLWS, IN, imgfile, IOCTL, jpeg, panel, panelparser, readcd, sgi, sv/SV, torgb, WAIT.
  • Removed obsolete functions: commands.getstatus(), os.popen*().
  • Removed functions in the string module that are also string methods; Remove string.{letters, lowercase, uppercase}.
  • Removed support for long obsolete platforms: plat-aix3, plat-irix5.
  • Removed xmlrpclib.SlowParser. It was based on xmllib.
  • Patch #1680961: atexit has been reimplemented in C.
  • Add new codecs for UTF-32, UTF-32-LE and UTF-32-BE.



  • Removed these Python slots: __coerce__, __div__, __idiv__, __rdiv__.
  • Removed these C APIs: PyNumber_Coerce(), PyNumber_CoerceEx(), PyMember_Get, PyMember_Set.
  • Removed these C slots/fields: nb_divide, nb_inplace_divide.
  • Removed these macros: staticforward, statichere, PyArg_GetInt, PyArg_NoArgs, _PyObject_Del.
  • Removed these typedefs: intargfunc, intintargfunc, intobjargproc, intintobjargproc, getreadbufferproc, getwritebufferproc, getsegcountproc, getcharbufferproc, memberlist.


  • Removed test.testall as test.regrtest replaces it.



  • The cfmfile module was removed.


  • Support for BeOS and AtheOS was removed (according to PEP 11).
  • Support for RiscOS, Irix, Tru64 was removed (alledgedly).


(For information about older versions, consult the HISTORY file.)