What's New in Python 2.2a2? =========================== Tools - The new Tools/scripts/cleanfuture.py can be used to automatically edit out obsolete future statements from Python source code. See the module docstring for details. Tests - regrtest.py now knows which tests are expected to be skipped on some platforms, allowing to give clearer test result output. - Several new tests in the standard test suite, with special thanks to Nick Mathewson. Core - Warnings about a mismatch in the Python API during extension import now use the Python warning framework (which makes it possible to write filters for these warnings). - A function's __dict__ (aka func_dict) will now always be a dictionary. It used to be possible to delete it or set it to None, but now both actions raise TypeErrors. It is still legal to set it to a dictionary object. Getting func.__dict__ before any attributes have been assigned now returns an empty dictionary instead of None. Library - New class Differ and new functions ndiff() and restore() in difflib.py. These package the algorithms used by the popular Tools/scripts/ndiff.py, for programmatic reuse. - New function xml.sax.saxutils.quoteattr(): Quote an XML attribute value using the minimal quoting required for the value; more reliable than using xml.sax.saxutils.escape() for attribute values. - Readline completion support for cmd.Cmd was added. New platforms C API - Two new APIs PyOS_snprintf() and PyOS_vsnprintf() were added which provide a cross-platform implementations for the relatively new snprintf()/vsnprintf() C lib APIs. In contrast to the standard sprintf() and vsprintf() C lib APIs, these versions apply bounds checking on the used buffer which enhances protection against buffer overruns. - Unicode APIs now use name mangling to assure that mixing interpreters and extensions using different Unicode widths is rendered next to impossible. Trying to import an incompatible Unicode-aware extension will result in an ImportError. Unicode extensions writers must make sure to check the Unicode width compatibility in their extensions by using at least one of the mangled Unicode APIs in the extension. Windows - "import module" now compiles module.pyw if it exists and nothing else relevant is found. What's New in Python 2.2a1? =========================== Core - TENTATIVELY, a large amount of code implementing much of what's described in PEP 252 (Making Types Look More Like Classes) and PEP 253 (Subtyping Built-in Types) was added. This will be released with Python 2.2a1. Documentation will be provided separately through http://www.python.org/2.2/. The purpose of releasing this with Python 2.2a1 is to test backwards compatibility. It is possible, though not likely, that a decision is made not to release this code as part of 2.2 final, if any serious backwards incompapatibilities are found during alpha testing that cannot be repaired. - 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 constants ascii_letters, ascii_lowercase. and ascii_uppercase were added to the string module. These a locale-indenpendent constants, unlike letters, lowercase, and uppercase. These are now use in appropriate locations in the standard 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 /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]) 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! What's New in Python 2.0? ========================= Below is a list of all relevant changes since release 1.6. Older changes are in the file HISTORY. If you are making the jump directly from Python 1.5.2 to 2.0, make sure to read the section for 1.6 in the HISTORY file! Many important changes listed there. Alternatively, a good overview of the changes between 1.5.2 and 2.0 is the document "What's New in Python 2.0" by Kuchling and Moshe Zadka: http://starship.python.net/crew/amk/python/writing/new-python/. --Guido van Rossum (home page: http://www.pythonlabs.com/~guido/) ====================================================================== What's new in 2.0 (since release candidate 1)? ============================================== Standard library - The copy_reg module was modified to clarify its intended use: to register pickle support for extension types, not for classes. pickle() will raise a TypeError if it is passed a class. - Fixed a bug in gettext's "normalize and expand" code that prevented it from finding an existing .mo file. - Restored support for HTTP/0.9 servers in httplib. - The math module was changed to stop raising OverflowError in case of underflow, and return 0 instead in underflow cases. Whether Python used to raise OverflowError in case of underflow was platform- dependent (it did when the platform math library set errno to ERANGE on underflow). - Fixed a bug in StringIO that occurred when the file position was not at the end of the file and write() was called with enough data to extend past the end of the file. - Fixed a bug that caused Tkinter error messages to get lost on Windows. The bug was fixed by replacing direct use of interp->result with Tcl_GetStringResult(interp). - Fixed bug in urllib2 that caused it to fail when it received an HTTP redirect response. - Several changes were made to distutils: Some debugging code was removed from util. Fixed the installer used when an external zip program (like WinZip) is not found; the source code for this installer is in Misc/distutils. check_lib() was modified to behave more like AC_CHECK_LIB by add other_libraries() as a parameter. The test for whether installed modules are on sys.path was changed to use both normcase() and normpath(). - Several minor bugs were fixed in the xml package (the minidom, pulldom, expatreader, and saxutils modules). - The regression test driver (regrtest.py) behavior when invoked with -l changed: It now reports a count of objects that are recognized as garbage but not freed by the garbage collector. - The regression test for the math module was changed to test exceptional behavior when the test is run in verbose mode. Python cannot yet guarantee consistent exception behavior across platforms, so the exception part of test_math is run only in verbose mode, and may fail on your platform. Internals - PyOS_CheckStack() has been disabled on Win64, where it caused test_sre to fail. Build issues - Changed compiler flags, so that gcc is always invoked with -Wall and -Wstrict-prototypes. Users compiling Python with GCC should see exactly one warning, except if they have passed configure the --with-pydebug flag. The expected warning is for getopt() in Modules/main.c. This warning will be fixed for Python 2.1. - Fixed configure to add -threads argument during linking on OSF1. Tools and other miscellany - The compiler in Tools/compiler was updated to support the new language features introduced in 2.0: extended print statement, list comprehensions, and augmented assignments. The new compiler should also be backwards compatible with Python 1.5.2; the compiler will always generate code for the version of the interpreter it runs under. What's new in 2.0 release candidate 1 (since beta 2)? ===================================================== What is release candidate 1? We believe that release candidate 1 will fix all known bugs that we intend to fix for the 2.0 final release. This release should be a bit more stable than the previous betas. We would like to see even more widespread testing before the final release, so we are producing this release candidate. The final release will be exactly the same unless any show-stopping (or brown bag) bugs are found by testers of the release candidate. All the changes since the last beta release are bug fixes or changes to support building Python for specific platforms. Core language, builtins, and interpreter - A bug that caused crashes when __coerce__ was used with augmented assignment, e.g. +=, was fixed. - Raise ZeroDivisionError when raising zero to a negative number, e.g. 0.0 ** -2.0. Note that math.pow is unrelated to the builtin power operator and the result of math.pow(0.0, -2.0) will vary by platform. On Linux, it raises a ValueError. - A bug in Unicode string interpolation was fixed that occasionally caused errors with formats including "%%". For example, the following expression "%% %s" % u"abc" no longer raises a TypeError. - Compilation of deeply nested expressions raises MemoryError instead of SyntaxError, e.g. eval("[" * 50 + "]" * 50). - In 2.0b2 on Windows, the interpreter wrote .pyc files in text mode, rendering them useless. They are now written in binary mode again. Standard library - Keyword arguments are now accepted for most pattern and match object methods in SRE, the standard regular expression engine. - In SRE, fixed error with negative lookahead and lookbehind that manifested itself as a runtime error in patterns like "(? is now included by Python.h (if it exists). INT_MAX and LONG_MAX will always be defined, even if is not available. - PyFloat_FromString takes a second argument, pend, that was effectively useless. It is now officially useless but preserved for backwards compatibility. If the pend argument is not NULL, *pend is set to NULL. - PyObject_GetAttr() and PyObject_SetAttr() now accept Unicode objects for the attribute name. See note on getattr() above. - A few bug fixes to argument processing for Unicode. PyArg_ParseTupleAndKeywords() now accepts "es#" and "es". PyArg_Parse() special cases "s#" for Unicode objects; it returns a pointer to the default encoded string data instead of to the raw UTF-16. - Py_BuildValue accepts B format (for bgen-generated code). Internals - On Unix, fix code for finding Python installation directory so that it works when argv[0] is a relative path. - Added a true unicode_internal_encode() function and fixed the unicode_internal_decode function() to support Unicode objects directly rather than by generating a copy of the object. - Several of the internal Unicode tables are much smaller now, and the source code should be much friendlier to weaker compilers. - In the garbage collector: Fixed bug in collection of tuples. Fixed bug that caused some instances to be removed from the container set while they were still live. Fixed parsing in gc.set_debug() for platforms where sizeof(long) > sizeof(int). - Fixed refcount problem in instance deallocation that only occurred when Py_REF_DEBUG was defined and Py_TRACE_REFS was not. - On Windows, getpythonregpath is now protected against null data in registry key. - On Unix, create .pyc/.pyo files with O_EXCL flag to avoid a race condition. Build and platform-specific issues - Better support of GNU Pth via --with-pth configure option. - Python/C API now properly exposed to dynamically-loaded extension modules on Reliant UNIX. - Changes for the benefit of SunOS 4.1.4 (really!). mmapmodule.c: Don't define MS_SYNC to be zero when it is undefined. Added missing prototypes in posixmodule.c. - Improved support for HP-UX build. Threads should now be correctly configured (on HP-UX 10.20 and 11.00). - Fix largefile support on older NetBSD systems and OpenBSD by adding define for TELL64. Tools and other miscellany - ftpmirror: Call to main() is wrapped in if __name__ == "__main__". - freeze: The modulefinder now works with 2.0 opcodes. - IDLE: Move hackery of sys.argv until after the Tk instance has been created, which allows the application-specific Tkinter initialization to be executed if present; also pass an explicit className parameter to the Tk() constructor. What's new in 2.0 beta 1? ========================= Source Incompatibilities ------------------------ None. Note that 1.6 introduced several incompatibilities with 1.5.2, such as single-argument append(), connect() and bind(), and changes to str(long) and repr(float). Binary Incompatibilities ------------------------ - Third party extensions built for Python 1.5.x or 1.6 cannot be used with Python 2.0; these extensions will have to be rebuilt for Python 2.0. - On Windows, attempting to import a third party extension built for Python 1.5.x or 1.6 results in an immediate crash; there's not much we can do about this. Check your PYTHONPATH environment variable! - Python bytecode files (*.pyc and *.pyo) are not compatible between releases. Overview of Changes Since 1.6 ----------------------------- There are many new modules (including brand new XML support through the xml package, and i18n support through the gettext module); a list of all new modules is included below. Lots of bugs have been fixed. The process for making major new changes to the language has changed since Python 1.6. Enhancements must now be documented by a Python Enhancement Proposal (PEP) before they can be accepted. There are several important syntax enhancements, described in more detail below: - Augmented assignment, e.g. x += 1 - List comprehensions, e.g. [x**2 for x in range(10)] - Extended import statement, e.g. import Module as Name - Extended print statement, e.g. print >> file, "Hello" Other important changes: - Optional collection of cyclical garbage Python Enhancement Proposal (PEP) --------------------------------- PEP stands for Python Enhancement Proposal. A PEP is a design document providing information to the Python community, or describing a new feature for Python. The PEP should provide a concise technical specification of the feature and a rationale for the feature. We intend PEPs to be the primary mechanisms for proposing new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python. The PEP author is responsible for building consensus within the community and documenting dissenting opinions. The PEPs are available at http://python.sourceforge.net/peps/. Augmented Assignment -------------------- This must have been the most-requested feature of the past years! Eleven new assignment operators were added: += -= *= /= %= **= <<= >>= &= ^= |= For example, A += B is similar to A = A + B except that A is evaluated only once (relevant when A is something like dict[index].attr). However, if A is a mutable object, A may be modified in place. Thus, if A is a number or a string, A += B has the same effect as A = A+B (except A is only evaluated once); but if a is a list, A += B has the same effect as A.extend(B)! Classes and built-in object types can override the new operators in order to implement the in-place behavior; the not-in-place behavior is used automatically as a fallback when an object doesn't implement the in-place behavior. For classes, the method name is derived from the method name for the corresponding not-in-place operator by inserting an 'i' in front of the name, e.g. __iadd__ implements in-place __add__. Augmented assignment was implemented by Thomas Wouters. List Comprehensions ------------------- This is a flexible new notation for lists whose elements are computed from another list (or lists). The simplest form is: [ for in ] For example, [i**2 for i in range(4)] yields the list [0, 1, 4, 9]. This is more efficient than a for loop with a list.append() call. You can also add a condition: [ for in if ] For example, [w for w in words if w == w.lower()] would yield the list of words that contain no uppercase characters. This is more efficient than a for loop with an if statement and a list.append() call. You can also have nested for loops and more than one 'if' clause. For example, here's a function that flattens a sequence of sequences:: def flatten(seq): return [x for subseq in seq for x in subseq] flatten([[0], [1,2,3], [4,5], [6,7,8,9], []]) This prints [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] List comprehensions originated as a patch set from Greg Ewing; Skip Montanaro and Thomas Wouters also contributed. Described by PEP 202. Extended Import Statement ------------------------- Many people have asked for a way to import a module under a different name. This can be accomplished like this: import foo bar = foo del foo but this common idiom gets old quickly. A simple extension of the import statement now allows this to be written as follows: import foo as bar There's also a variant for 'from ... import': from foo import bar as spam This also works with packages; e.g. you can write this: import test.regrtest as regrtest Note that 'as' is not a new keyword -- it is recognized only in this context (this is only possible because the syntax for the import statement doesn't involve expressions). Implemented by Thomas Wouters. Described by PEP 221. Extended Print Statement ------------------------ Easily the most controversial new feature, this extension to the print statement adds an option to make the output go to a different file than the default sys.stdout. For example, to write an error message to sys.stderr, you can now write: print >> sys.stderr, "Error: bad dog!" As a special feature, if the expression used to indicate the file evaluates to None, the current value of sys.stdout is used. Thus: print >> None, "Hello world" is equivalent to print "Hello world" Design and implementation by Barry Warsaw. Described by PEP 214. Optional Collection of Cyclical Garbage --------------------------------------- Python is now equipped with a garbage collector that can hunt down cyclical references between Python objects. It's no replacement for reference counting; in fact, it depends on the reference counts being correct, and decides that a set of objects belong to a cycle if all their reference counts can be accounted for from their references to each other. This devious scheme was first proposed by Eric Tiedemann, and brought to implementation by Neil Schemenauer. There's a module "gc" that lets you control some parameters of the garbage collection. There's also an option to the configure script that lets you enable or disable the garbage collection. In 2.0b1, it's on by default, so that we (hopefully) can collect decent user experience with this new feature. There are some questions about its performance. If it proves to be too much of a problem, we'll turn it off by default in the final 2.0 release. Smaller Changes --------------- A new function zip() was added. zip(seq1, seq2, ...) is equivalent to map(None, seq1, seq2, ...) when the sequences have the same length; i.e. zip([1,2,3], [10,20,30]) returns [(1,10), (2,20), (3,30)]. When the lists are not all the same length, the shortest list wins: zip([1,2,3], [10,20]) returns [(1,10), (2,20)]. See PEP 201. sys.version_info is a tuple (major, minor, micro, level, serial). Dictionaries have an odd new method, setdefault(key, default). dict.setdefault(key, default) returns dict[key] if it exists; if not, it sets dict[key] to default and returns that value. Thus: dict.setdefault(key, []).append(item) does the same work as this common idiom: if not dict.has_key(key): dict[key] = [] dict[key].append(item) There are two new variants of SyntaxError that are raised for indentation-related errors: IndentationError and TabError. Changed \x to consume exactly two hex digits; see PEP 223. Added \U escape that consumes exactly eight hex digits. The limits on the size of expressions and file in Python source code have been raised from 2**16 to 2**32. Previous versions of Python were limited because the maximum argument size the Python VM accepted was 2**16. This limited the size of object constructor expressions, e.g. [1,2,3] or {'a':1, 'b':2}, and the size of source files. This limit was raised thanks to a patch by Charles Waldman that effectively fixes the problem. It is now much more likely that you will be limited by available memory than by an arbitrary limit in Python. The interpreter's maximum recursion depth can be modified by Python programs using sys.getrecursionlimit and sys.setrecursionlimit. This limit is the maximum number of recursive calls that can be made by Python code. The limit exists to prevent infinite recursion from overflowing the C stack and causing a core dump. The default value is 1000. The maximum safe value for a particular platform can be found by running Misc/find_recursionlimit.py. New Modules and Packages ------------------------ atexit - for registering functions to be called when Python exits. imputil - Greg Stein's alternative API for writing custom import hooks. pyexpat - an interface to the Expat XML parser, contributed by Paul Prescod. xml - a new package with XML support code organized (so far) in three subpackages: xml.dom, xml.sax, and xml.parsers. Describing these would fill a volume. There's a special feature whereby a user-installed package named _xmlplus overrides the standard xmlpackage; this is intended to give the XML SIG a hook to distribute backwards-compatible updates to the standard xml package. webbrowser - a platform-independent API to launch a web browser. Changed Modules --------------- array -- new methods for array objects: count, extend, index, pop, and remove binascii -- new functions b2a_hex and a2b_hex that convert between binary data and its hex representation calendar -- Many new functions that support features including control over which day of the week is the first day, returning strings instead of printing them. Also new symbolic constants for days of week, e.g. MONDAY, ..., SUNDAY. cgi -- FieldStorage objects have a getvalue method that works like a dictionary's get method and returns the value attribute of the object. ConfigParser -- The parser object has new methods has_option, remove_section, remove_option, set, and write. They allow the module to be used for writing config files as well as reading them. ftplib -- ntransfercmd(), transfercmd(), and retrbinary() all now optionally support the RFC 959 REST command. gzip -- readline and readlines now accept optional size arguments httplib -- New interfaces and support for HTTP/1.1 by Greg Stein. See the module doc strings for details. locale -- implement getdefaultlocale for Win32 and Macintosh marshal -- no longer dumps core when marshaling deeply nested or recursive data structures os -- new functions isatty, seteuid, setegid, setreuid, setregid os/popen2 -- popen2/popen3/popen4 support under Windows. popen2/popen3 support under Unix. os/pty -- support for openpty and forkpty os.path -- fix semantics of os.path.commonprefix smtplib -- support for sending very long messages socket -- new function getfqdn() readline -- new functions to read, write and truncate history files. The readline section of the library reference manual contains an example. select -- add interface to poll system call shutil -- new copyfileobj function SimpleHTTPServer, CGIHTTPServer -- Fix problems with buffering in the HTTP server. Tkinter -- optimization of function flatten urllib -- scans environment variables for proxy configuration, e.g. http_proxy. whichdb -- recognizes dumbdbm format Obsolete Modules ---------------- None. However note that 1.6 made a whole slew of modules obsolete: stdwin, soundex, cml, cmpcache, dircache, dump, find, grep, packmail, poly, zmod, strop, util, whatsound. Changed, New, Obsolete Tools ---------------------------- None. C-level Changes --------------- Several cleanup jobs were carried out throughout the source code. All C code was converted to ANSI C; we got rid of all uses of the Py_PROTO() macro, which makes the header files a lot more readable. Most of the portability hacks were moved to a new header file, pyport.h; several other new header files were added and some old header files were removed, in an attempt to create a more rational set of header files. (Few of these ever need to be included explicitly; they are all included by Python.h.) Trent Mick ensured portability to 64-bit platforms, under both Linux and Win64, especially for the new Intel Itanium processor. Mick also added large file support for Linux64 and Win64. The C APIs to return an object's size have been update to consistently use the form PyXXX_Size, e.g. PySequence_Size and PyDict_Size. In previous versions, the abstract interfaces used PyXXX_Length and the concrete interfaces used PyXXX_Size. The old names, e.g. PyObject_Length, are still available for backwards compatibility at the API level, but are deprecated. The PyOS_CheckStack function has been implemented on Windows by Fredrik Lundh. It prevents Python from failing with a stack overflow on Windows. The GC changes resulted in creation of two new slots on object, tp_traverse and tp_clear. The augmented assignment changes result in the creation of a new slot for each in-place operator. The GC API creates new requirements for container types implemented in C extension modules. See Include/objimpl.h for details. PyErr_Format has been updated to automatically calculate the size of the buffer needed to hold the formatted result string. This change prevents crashes caused by programmer error. New C API calls: PyObject_AsFileDescriptor, PyErr_WriteUnraisable. PyRun_AnyFileEx, PyRun_SimpleFileEx, PyRun_FileEx -- New functions that are the same as their non-Ex counterparts except they take an extra flag argument that tells them to close the file when done. XXX There were other API changes that should be fleshed out here. Windows Changes --------------- New popen2/popen3/peopen4 in os module (see Changed Modules above). os.popen is much more usable on Windows 95 and 98. See Microsoft Knowledge Base article Q150956. The Win9x workaround described there is implemented by the new w9xpopen.exe helper in the root of your Python installation. Note that Python uses this internally; it is not a standalone program. Administrator privileges are no longer required to install Python on Windows NT or Windows 2000. If you have administrator privileges, Python's registry info will be written under HKEY_LOCAL_MACHINE. Otherwise the installer backs off to writing Python's registry info under HKEY_CURRENT_USER. The latter is sufficient for all "normal" uses of Python, but will prevent some advanced uses from working (for example, running a Python script as an NT service, or possibly from CGI). [This was new in 1.6] The installer no longer runs a separate Tcl/Tk installer; instead, it installs the needed Tcl/Tk files directly in the Python directory. If you already have a Tcl/Tk installation, this wastes some disk space (about 4 Megs) but avoids problems with conflicting Tcl/Tk installations, and makes it much easier for Python to ensure that Tcl/Tk can find all its files. [This was new in 1.6] The Windows installer now installs by default in \Python20\ on the default volume, instead of \Program Files\Python-2.0\. Updates to the changes between 1.5.2 and 1.6 -------------------------------------------- The 1.6 NEWS file can't be changed after the release is done, so here is some late-breaking news: New APIs in locale.py: normalize(), getdefaultlocale(), resetlocale(), and changes to getlocale() and setlocale(). The new module is now enabled per default. It is not true that the encodings codecs cannot be used for normal strings: the string.encode() (which is also present on 8-bit strings !) allows using them for 8-bit strings too, e.g. to convert files from cp1252 (Windows) to latin-1 or vice-versa. Japanese codecs are available from Tamito KAJIYAMA: http://pseudo.grad.sccs.chukyo-u.ac.jp/~kajiyama/python/ ======================================================================