Misc/NEWS

What's New in Python 2.3 alpha 1?
XXX Release date: DD-MMM-2002 XXX
=================================

Type/class unification and new-style classes

- Assignment to __class__ is disallowed if either the old and the new
  class is a statically allocated type object (such as defined by an
  extension module).  This prevents anomalies like 2.__class__ = bool.

- New-style object creation and deallocation have been sped up
  significantly; they are now faster than classic instance creation
  and deallocation.

- The __slots__ variable can now mention "private" names, and the
  right thing will happen (e.g. __slots__ = ["__foo"]).

- The built-ins slice() and buffer() are now callable types.  The
  types classobj (formerly class), code, function, instance, and
  instancemethod (formerly instance-method), which have no built-in
  names but are accessible through the types module, are now also
  callable.  The type dict-proxy is renamed to dictproxy.

- Cycles going through the __class__ link of a new-style instance are
  now detected by the garbage collector.

- Classes using __slots__ are now properly garbage collected.
  [SF bug 519621]

- Tightened the __slots__ rules: a slot name must be a valid Python
  identifier.

- The constructor for the module type now requires a name argument and
  takes an optional docstring argument.  Previously, this constructor
  ignored its arguments.  As a consequence, deriving a class from a
  module (not from the module type) is now illegal; previously this
  created an unnamed module, just like invoking the module type did.
  [SF bug 563060]

- A new type object, 'basestring', is added.  This is a common base type
  for 'str' and 'unicode', and can be used instead of
  types.StringTypes, e.g. to test whether something is "a string":
  isinstance(x, basestring) is True for Unicode and 8-bit strings.  This
  is an abstract base class and cannot be instantiated directly.

- Changed new-style class instantiation so that when C's __new__
  method returns something that's not a C instance, its __init__ is
  not called.  [SF bug #537450]

- Fixed super() to work correctly with class methods.  [SF bug #535444]

- If you try to pickle an instance of a class that has __slots__ but
  doesn't define or override __getstate__, a TypeError is now raised.
  This is done by adding a bozo __getstate__ to the class that always
  raises TypeError.  (Before, this would appear to be pickled, but the
  state of the slots would be lost.)

Core and builtins

- Codec error handling callbacks (PEP 293) are implemented.
  Error handling in unicode.encode or str.decode can now be customized.

- A subtle change to the semantics of the built-in function intern():
  interned strings are no longer immortal.  You must keep a reference
  to the return value intern() around to get the benefit.

- Use of 'None' as a variable, argument or attribute name now
  issues a SyntaxWarning.  In the future, None may become a keyword.

- SET_LINENO is gone.  co_lnotab is now consulted to determine when to
  call the trace function.  C code that accessed f_lineno should call
  PyCode_Addr2Line instead (f_lineno is still there, but not kept up
  to date).

- There's a new warning category, FutureWarning.  This is used to warn
  about a number of situations where the value or sign of an integer
  result will change in Python 2.4 as a result of PEP 237 (integer
  unification).  The warnings implement stage B0 mentioned in that
  PEP.  The warnings are about the following situations:

    - Octal and hex literals without 'L' prefix in the inclusive range
      [0x80000000..0xffffffff]; these are currently negative ints, but
      in Python 2.4 they will be positive longs with the same bit
      pattern.

    - Left shifts on integer values that cause the outcome to lose
      bits or have a different sign than the left operand.  To be
      precise: x<<n where this currently doesn't yield the same value
      as long(x)<<n; in Python 2.4, the outcome will be long(x)<<n.

    - Conversions from ints to string that show negative values as
      unsigned ints in the inclusive range [0x80000000..0xffffffff];
      this affects the functions hex() and oct(), and the string
      formatting codes %u, %o, %x, and %X.  In Python 2.4, these will
      show signed values (e.g. hex(-1) currently returns "0xffffffff";
      in Python 2.4 it will return "-0x1").

- When multiplying very large integers, a version of the so-called
  Karatsuba algorithm is now used.  This is most effective if the
  inputs have roughly the same size.  If they both have about N digits,
  Karatsuba multiplication has O(N**1.58) runtime (the exponent is
  log_base_2(3)) instead of the previous O(N**2).  Measured results may
  be better or worse than that, depending on platform quirks.  Besides
  the O() improvement in raw instruction count, the Karatsuba algorithm
  appears to have much better cache behavior on extremely large integers
  (starting in the ballpark of a million bits).  Note that this is a
  simple implementation, and there's no intent here to compete with,
  e.g., GMP.  It gives a very nice speedup when it applies, but a package
  devoted to fast large-integer arithmetic should run circles around it.

- u'%c' will now raise a ValueError in case the argument is an
  integer outside the valid range of Unicode code point ordinals.

- The tempfile module has been overhauled for enhanced security.  The
  mktemp() function is now deprecated; new, safe replacements are
  mkstemp() (for files) and mkdtemp() (for directories), and the
  higher-level functions NamedTemporaryFile() and TemporaryFile().
  Use of some global variables in this module is also deprecated; the
  new functions have keyword arguments to provide the same
  functionality.  All Lib, Tools and Demo modules that used the unsafe
  interfaces have been updated to use the safe replacements.  Thanks
  to Zack Weinberg!

- When x is an object whose class implements __mul__ and __rmul__,
  1.0*x would correctly invoke __rmul__, but 1*x would erroneously
  invoke __mul__.  This was due to the sequence-repeat code in the int
  type.  This has been fixed now.

- Previously, "str1 in str2" required str1 to be a string of length 1.
  This restriction has been relaxed to allow str1 to be a string of
  any length.  Thus "'el' in 'hello world'" returns True now.

- File objects are now their own iterators.  For a file f, iter(f) now
  returns f (unless f is closed), and f.next() is similar to
  f.readline() when EOF is not reached; however, f.next() uses a
  readahead buffer that messes up the file position, so mixing
  f.next() and f.readline() (or other methods) doesn't work right.
  Calling f.seek() drops the readahead buffer, but other operations
  don't.  It so happens that this gives a nice additional speed boost
  to "for line in file:"; the xreadlines method and corresponding
  module are now obsolete.  Thanks to Oren Tirosh!

- Encoding declarations (PEP 263, phase 1) have been implemented.  A
  comment of the form "# -*- coding: <encodingname> -*-" in the first
  or second line of a Python source file indicates the encoding.

- list.sort() has a new implementation.  While cross-platform results
  may vary, and in data-dependent ways, this is much faster on many
  kinds of partially ordered lists than the previous implementation,
  and reported to be just as fast on randomly ordered lists on
  several major platforms.  This sort is also stable (if A==B and A
  precedes B in the list at the start, A precedes B after the sort too),
  although the language definition does not guarantee stability.  A
  potential drawback is that list.sort() may require temp space of
  len(list)*2 bytes (*4 on a 64-bit machine).  It's therefore possible
  for list.sort() to raise MemoryError now, even if a comparison function
  does not.  See <http://www.python.org/sf/587076> for full details.

- All standard iterators now ensure that, once StopIteration has been
  raised, all future calls to next() on the same iterator will also
  raise StopIteration.  There used to be various counterexamples to
  this behavior, which could caused confusion or subtle program
  breakage, without any benefits.  (Note that this is still an
  iterator's responsibility; the iterator framework does not enforce
  this.)

- Ctrl+C handling on Windows has been made more consistent with
  other platforms.  KeyboardInterrupt can now reliably be caught,
  and Ctrl+C at an interactive prompt no longer terminates the
  process under NT/2k/XP (it never did under Win9x).  Ctrl+C will
  interrupt time.sleep() in the main thread, and any child processes
  created via the popen family (on win2k; we can't make win9x work
  reliably) are also interrupted (as generally happens on for Linux/Unix.)
  [SF bugs 231273, 439992 and 581232]

- Slices and repetitions of buffer objects now consistently return
  a string.  Formerly, strings would be returned most of the time,
  but a buffer object would be returned when the repetition count
  was one or when the slice range was all inclusive.

- Unicode objects in sys.path are no longer ignored but treated
  as directory names.

- Fixed string.startswith and string.endswith builtin methods
  so they accept negative indices.  [SF bug 493951]

- Fixed a bug with a continue inside a try block and a yield in the
  finally clause.  [SF bug 567538]

- Most builtin sequences now support "extended slices", i.e. slices
  with a third "stride" parameter.  For example, "hello world"[::-1]
  gives "dlrow olleh".

- A new warning PendingDeprecationWarning was added to provide
  direction on features which are in the process of being deprecated.
  The warning will not be printed by default.  To see the pending
  deprecations, use -Walways::PendingDeprecationWarning::
  as a command line option or warnings.filterwarnings() in code.

- Deprecated features of xrange objects have been removed as
  promised.  The start, stop, and step attributes and the tolist()
  method no longer exist.  xrange repetition and slicing have been
  removed.

- New builtin function enumerate(x), from PEP 279.  Example:
  enumerate("abc") is an iterator returning (0,"a"), (1,"b"), (2,"c").
  The argument can be an arbitrary iterable object.

- The assert statement no longer tests __debug__ at runtime.  This means
  that assert statements cannot be disabled by assigning a false value
  to __debug__.

- A method zfill() was added to str and unicode, that fills a numeric
  string to the left with zeros.  For example,
  "+123".zfill(6) -> "+00123".

- Complex numbers supported divmod() and the // and % operators, but
  these make no sense.  Since this was documented, they're being
  deprecated now.

- String and unicode methods lstrip(), rstrip() and strip() now take
  an optional argument that specifies the characters to strip.  For
  example, "Foo!!!?!?!?".rstrip("?!") -> "Foo".

- Added a new dict method pop(key).  This removes and returns the
  value corresponding to key.  [SF patch #539949]

- A new built-in type, bool, has been added, as well as built-in
  names for its two values, True and False.  Comparisons and sundry
  other operations that return a truth value have been changed to
  return a bool instead.  Read PEP 285 for an explanation of why this
  is backward compatible.

- Fixed two bugs reported as SF #535905: under certain conditions,
  deallocating a deeply nested structure could cause a segfault in the
  garbage collector, due to interaction with the "trashcan" code;
  access to the current frame during destruction of a local variable
  could access a pointer to freed memory.

- The optional object allocator ("pymalloc") has been enabled by
  default.  The recommended practice for memory allocation and
  deallocation has been streamlined.  A header file is included,
  Misc/pymemcompat.h, which can be bundled with 3rd party extensions
  and lets them use the same API with Python versions from 1.5.2
  onwards.

- PyErr_Display will provide file and line information for all exceptions
  that have an attribute print_file_and_line, not just SyntaxErrors.

- The UTF-8 codec will now encode and decode Unicode surrogates
  correctly and without raising exceptions for unpaired ones.

- Universal newlines (PEP 278) is implemented.  Briefly, using 'U'
  instead of 'r' when opening a text file for reading changes the line
  ending convention so that any of '\r', '\r\n', and '\n' is
  recognized (even mixed in one file); all three are converted to
  '\n', the standard Python line end character.

- file.xreadlines() now raises a ValueError if the file is closed:
  Previously, an xreadlines object was returned which would raise
  a ValueError when the xreadlines.next() method was called.

- sys.exit() inadvertently allowed more than one argument.
  An exception will now be raised if more than one argument is used.

Extension modules

- The xreadlines module is slated for obsolescence.

- The strptime function in the time module is now always available (a
  Python implementation is used when the C library doesn't define it).

- The 'new' module is no longer an extension, but a Python module that
  only exists for backwards compatibility.  Its contents are no longer
  functions but callable type objects.

- The bsddb.*open functions can now take 'None' as a filename.
  This will create a temporary in-memory bsddb that won't be
  written to disk.

- posix.lchown, posix.killpg, posix.mknod, and posix.getpgid have been
  added where available.

- The locale module now exposes the C library's gettext interface.

- A security hole ("double free") was found in zlib-1.1.3, a popular
  third party compression library used by some Python modules.  The
  hole was quickly plugged in zlib-1.1.4, and the Windows build of
  Python now ships with zlib-1.1.4.

- pwd, grp, and resource return enhanced tuples now, with symbolic
  field names.

- array.array is now a type object. A new format character
  'u' indicates Py_UNICODE arrays. For those, .tounicode and
  .fromunicode methods are available. Arrays now support __iadd__
  and __imul__.

- dl now builds on every system that has dlfcn.h.  Failure in case
  of sizeof(int)!=sizeof(long)!=sizeof(void*) is delayed until dl.open
  is called.

- signal.sigpending, signal.sigprocmask and signal.sigsuspend have
  been added where available.

- The sys module acquired a new attribute, api_version, which evaluates
  to the value of the PYTHON_API_VERSION macro with which the
  interpreter was compiled.

Library

- New module: sets, defines the class Set that implements a mutable
  set type using the keys of a dict to represent the set.  There's
  also a class ImmutableSet which is useful when you need sets of sets
  or when you need to use sets as dict keys, and a class BaseSet which
  is the base class of the two.  (This is not documented yet, but
  help(sets) gives a wealth of information.)

- Added operator.pow(a,b) which is equivalent to a**b.

- random.randrange(-sys.maxint-1, sys.maxint) no longer raises
  OverflowError.  That is, it now accepts any combination of 'start'
  and 'stop' arguments so long as each is in the range of Python's
  bounded integers.

- New "algorithms" module: heapq, implements a heap queue.  Thanks to
  Kevin O'Connor for the code and François Pinard for an entertaining
  write-up explaining the theory and practical uses of heaps.

- New encoding for the Palm OS character set: palmos.

- binascii.crc32() and the zipfile module had problems on some 64-bit
  platforms.  These have been fixed.  On a platform with 8-byte C longs,
  crc32() now returns a signed-extended 4-byte result, so that its value
  as a Python int is equal to the value computed a 32-bit platform.

- xml.dom.minidom.toxml and toprettyxml now take an optional encoding
  argument.

- Some fixes in the copy module: when an object is copied through its
  __reduce__ method, there was no check for a __setstate__ method on
  the result [SF patch 565085]; deepcopy should treat instances of
  custom metaclasses the same way it treats instances of type 'type'
  [SF patch 560794].

- Sockets now support timeout mode.  After s.settimeout(T), where T is
  a float expressing seconds, subsequent operations raise an exception
  if they cannot be completed within T seconds.  To disable timeout
  mode, use s.settimeout(None).  There's also a module function,
  socket.setdefaulttimeout(T), which sets the default for all sockets
  created henceforth.

- getopt.gnu_getopt was added.  This supports GNU-style option
  processing, where options can be mixed with non-option arguments.

- Stop using strings for exceptions.  String objects used for
  exceptions are now classes deriving from Exception.  The objects
  changed were: Tkinter.TclError, bdb.BdbQuit, macpath.norm_error,
  tabnanny.NannyNag, and xdrlib.Error.

- Constants BOM_UTF8, BOM_UTF16, BOM_UTF16_LE, BOM_UTF16_BE,
  BOM_UTF32, BOM_UTF32_LE and BOM_UTF32_BE that represent the Byte
  Order Mark in UTF-8, UTF-16 and UTF-32 encodings for little and
  big endian systems were added to the codecs module. The old names
  BOM32_* and BOM64_* were off by a factor of 2.

- Added conversion functions math.degrees() and math.radians().

- ftplib.retrlines() now tests for callback is None rather than testing
  for False.  Was causing an error when given a callback object which
  was callable but also returned len() as zero.  The change may
  create new breakage if the caller relied on the undocumented behavior
  and called with callback set to [] or some other False value not
  identical to None.

- random.gauss() uses a piece of hidden state used by nothing else,
  and the .seed() and .whseed() methods failed to reset it.  In other
  words, setting the seed didn't completely determine the sequence of
  results produced by random.gauss().  It does now.  Programs repeatedly
  mixing calls to a seed method with calls to gauss() may see different
  results now.

- The pickle.Pickler class grew a clear_memo() method to mimic that
  provided by cPickle.Pickler.

- difflib's SequenceMatcher class now does a dynamic analysis of
  which elements are so frequent as to constitute noise.  For
  comparing files as sequences of lines, this generally works better
  than the IS_LINE_JUNK function, and function ndiff's linejunk
  argument defaults to None now as a result.  A happy benefit is
  that SequenceMatcher may run much faster now when applied
  to large files with many duplicate lines (for example, C program
  text with lots of repeated "}" and "return NULL;" lines).

- New Text.dump() method in Tkinter module.

- New distutils commands for building packagers were added to
  support pkgtool on Solaris and swinstall on HP-UX.

- distutils now has a new abstract binary packager base class
  command/bdist_packager, which simplifies writing packagers.
  This will hopefully provide the missing bits to encourage
  people to submit more packagers, e.g. for Debian, FreeBSD
  and other systems.

- The UTF-16, -LE and -BE stream readers now raise a
  NotImplementedError for all calls to .readline(). Previously, they
  used to just produce garbage or fail with an encoding error --
  UTF-16 is a 2-byte encoding and the C lib's line reading APIs don't
  work well with these.

- compileall now supports quiet operation.

- The BaseHTTPServer now implements optional HTTP/1.1 persistent
  connections.

- socket module: the SSL support was broken out of the main
  _socket module C helper and placed into a new _ssl helper
  which now gets imported by socket.py if available and working.

- encodings package: added aliases for all supported IANA character
  sets

- ftplib: to safeguard the user's privacy, anonymous login will use
  "anonymous@" as default password, rather than the real user and host
  name.

- webbrowser: tightened up the command passed to os.system() so that
  arbitrary shell code can't be executed because a bogus URL was
  passed in.

- gettext.translation has an optional fallback argument, and
  gettext.find an optional all argument. Translations will now fallback
  on a per-message basis.

- distutils bdist commands now offer a --skip-build option.

- warnings.warn now accepts a Warning instance as first argument.

- The xml.sax.expatreader.ExpatParser class will no longer create
  circular references by using itself as the locator that gets passed
  to the content handler implementation.  [SF bug #535474]

- The email.Parser.Parser class now properly parses strings regardless
  of their line endings, which can be any of \r, \n, or \r\n (CR, LF,
  or CRLF).  Also, the Header class's constructor default arguments
  has changed slightly so that an explicit maxlinelen value is always
  honored.

Tools/Demos

- IDLE supports the new encoding declarations (PEP 263); it can also
  deal with legacy 8-bit files if they use the locale's encoding. It
  allows non-ASCII strings in the interactive shell and executes them
  in the locale's encoding.

- freeze.py now produces binaries which can import shared modules,
  unlike before when this failed due to missing symbol exports in
  the generated binary.

Build

- The public Python C API will generally be declared using PyAPI_FUNC
   and PyAPI_DATA macros, while Python extension module init functions
   will be declared with PyMODINIT_FUNC.  DL_EXPORT/DL_IMPORT macros
   are deprecated.

- A bug was fixed that could cause COUNT_ALLOCS builds to segfault, or
  get into infinite loops, when a new-style class got garbage-collected.
  Unfortunately, to avoid this, the way COUNT_ALLOCS works requires
  that new-style classes be immortal in COUNT_ALLOCS builds.  Note that
  COUNT_ALLOCS is not enabled by default, in either release or debug
  builds, and that new-style classes are immortal only in COUNT_ALLOCS
  builds.

- Compiling out the cyclic garbage collector is no longer an option.
  The old symbol WITH_CYCLE_GC is now ignored, and Python.h arranges
  that it's always defined (for the benefit of any extension modules
  that may be conditionalizing on it).  A bonus is that any extension
  type participating in cyclic gc can choose to participate in the
  Py_TRASHCAN mechanism now too; in the absence of cyclic gc, this used
  to require editing the core to teach the trashcan mechanism about the
  new type.

- According to Annex F of the current C standard,

    The Standard C macro HUGE_VAL and its float and long double analogs,
    HUGE_VALF and HUGE_VALL, expand to expressions whose values are
    positive infinities.

  Python only uses the double HUGE_VAL, and only to #define its own symbol
  Py_HUGE_VAL.  Some platforms have incorrect definitions for HUGE_VAL.
  pyport.h used to try to worm around that, but the workarounds triggered
  other bugs on other platforms, so we gave up.  If your platform defines
  HUGE_VAL incorrectly, you'll need to #define Py_HUGE_VAL to something
  that works on your platform.  The only instance of this I'm sure about
  is on an unknown subset of Cray systems, described here:

  http://www.cray.com/swpubs/manuals/SN-2194_2.0/html-SN-2194_2.0/x3138.htm

  Presumably 2.3a1 breaks such systems.  If anyone uses such a system, help!

- The configure option --without-doc-strings can be used to remove the
  doc strings from the builtin functions and modules; this reduces the
  size of the executable.

- The universal newlines option (PEP 278) is on by default.  On Unix
  it can be disabled by passing --without-universal-newlines to the
  configure script.  On other platforms, remove
  WITH_UNIVERSAL_NEWLINES from pyconfig.h.

- On Unix, a shared libpython2.3.so can be created with --enable-shared.

- All uses of the CACHE_HASH, INTERN_STRINGS, and DONT_SHARE_SHORT_STRINGS
  preprocessor symbols were eliminated.  The internal decisions they
  controlled stopped being experimental long ago.

- The tools used to build the documentation now work under Cygwin as
  well as Unix.

- The bsddb and dbm module builds have been changed to try and avoid version
  skew problems and disable linkage with Berkeley DB 1.85 unless the
  installer knows what s/he's doing.  See the section on building these
  modules in the README file for details.

C API

- The string object's layout has changed: the pointer member
  ob_sinterned has been replaced by an int member ob_sstate.  On some
  platforms (e.g. most 64-bit systems) this may change the offset of
  the ob_sval member, so as a precaution the API_VERSION has been
  incremented.  The apparently unused feature of "indirect interned
  strings", supported by the ob_sinterned member, is gone.  Interned
  strings are now usually mortal; theres a new API,
  PyString_InternImmortal() that creates immortal interned strings.
  (The ob_sstate member can only take three values; however, while
  making it a char saves a few bytes per string object on average, in
  it also slowed things down a bit because ob_sval was no longer
  aligned.)

- The Py_InitModule*() functions now accept NULL for the 'methods'
  argument.  Modules without global functions are becoming more common
  now that factories can be types rather than functions.

- New C API PyUnicode_FromOrdinal() which exposes unichr() at C
  level.

- New functions PyErr_SetExcFromWindowsErr() and
  PyErr_SetExcFromWindowsErrWithFilename(). Similar to
  PyErr_SetFromWindowsErrWithFilename() and
  PyErr_SetFromWindowsErr(), but they allow to specify
  the exception type to raise. Available on Windows.

- Py_FatalError() is now declared as taking a const char* argument.  It
  was previously declared without const.  This should not affect working
  code.

- Added new macro PySequence_ITEM(o, i) that directly calls
  sq_item without rechecking that o is a sequence and without
  adjusting for negative indices.

- PyRange_New() now raises ValueError if the fourth argument is not 1.
  This is part of the removal of deprecated features of the xrange
  object.

- PyNumber_Coerce() and PyNumber_CoerceEx() now also invoke the type's
  coercion if both arguments have the same type but this type has the
  CHECKTYPES flag set.  This is to better support proxies.

- The type of tp_free has been changed from "void (*)(PyObject *)" to
  "void (*)(void *)".

- PyObject_Del, PyObject_GC_Del are now functions instead of macros.

- A type can now inherit its metatype from its base type.  Previously,
  when PyType_Ready() was called, if ob_type was found to be NULL, it
  was always set to &PyType_Type; now it is set to base->ob_type,
  where base is tp_base, defaulting to &PyObject_Type.

- PyType_Ready() accidentally did not inherit tp_is_gc; now it does.

- The PyCore_* family of APIs have been removed.

- The "u#" parser marker will now pass through Unicode objects as-is
  without going through the buffer API.

- The enumerators of cmp_op have been renamed to use the prefix PyCmp_.

- An old #define of ANY as void has been removed from pyport.h.  This
  hasn't been used since Python's pre-ANSI days, and the #define has
  been marked as obsolete since then.  SF bug 495548 says it created
  conflicts with other packages, so keeping it around wasn't harmless.

- Because Python's magic number scheme broke on January 1st, we decided
  to stop Python development.  Thanks for all the fish!

- Some of us don't like fish, so we changed Python's magic number
  scheme to a new one. See Python/import.c for details.

New platforms

- AtheOS is now supported.

- the EMX runtime environment on OS/2 is now supported.

- GNU/Hurd is now supported.

Tests

Windows

- Sometimes the uninstall executable (UNWISE.EXE) vanishes.  One cause
  of that has been fixed in the installer (disabled Wise's "delete in-
  use files" uninstall option).

- Fixed a bug in urllib's proxy handling in Windows.  [SF bug #503031]

- The installer now installs Start menu shortcuts under (the local
  equivalent of) "All Users" when doing an Admin install.

- file.truncate([newsize]) now works on Windows for all newsize values.
  It used to fail if newsize didn't fit in 32 bits, reflecting a
  limitation of MS _chsize (which is no longer used).

- os.waitpid() is now implemented for Windows, and can be used to block
  until a specified process exits.  This is similar to, but not exactly
  the same as, os.waitpid() on POSIX systems.  If you're waiting for
  a specific process whose pid was obtained from one of the spawn()
  functions, the same Python os.waitpid() code works across platforms.
  See the docs for details.  The docs were changed to clarify that
  spawn functions return, and waitpid requires, a process handle on
  Windows (not the same thing as a Windows process id).

- New tempfile.TemporaryFile implementation for Windows:  this doesn't
  need a TemporaryFileWrapper wrapper anymore, and should be immune
  to a nasty problem:  before 2.3, if you got a temp file on Windows, it
  got wrapped in an object whose close() method first closed the
  underlying file, then deleted the file.  This usually worked fine.
  However, the spawn family of functions on Windows create (at a low C
  level) the same set of open files in the spawned process Q as were
  open in the spawning process P.  If a temp file f was among them, then
  doing f.close() in P first closed P's C-level file handle on f, but Q's
  C-level file handle on f remained open, so the attempt in P to delete f
  blew up with a "Permission denied" error (Windows doesn't allow
  deleting open files).  This was surprising, subtle, and difficult to
  work around.

- The os module now exports all the symbolic constants usable with the
  low-level os.open() on Windows:  the new constants in 2.3 are
  O_NOINHERIT, O_SHORT_LIVED, O_TEMPORARY, O_RANDOM and O_SEQUENTIAL.
  The others were also available in 2.2:  O_APPEND, O_BINARY, O_CREAT,
  O_EXCL, O_RDONLY, O_RDWR, O_TEXT, O_TRUNC and O_WRONLY.  Contrary
  to Microsoft docs, O_SHORT_LIVED does not seem to imply O_TEMPORARY
  (so specify both if you want both; note that neither is useful unless
  specified with O_CREAT too).

Mac


What's New in Python 2.2 final?
Release date: 21-Dec-2001
===============================

Type/class unification and new-style classes

- pickle.py, cPickle: allow pickling instances of new-style classes
  with a custom metaclass.

Core and builtins

- weakref proxy object: when comparing, unwrap both arguments if both
  are proxies.

Extension modules

- binascii.b2a_base64(): fix a potential buffer overrun when encoding
  very short strings.

- cPickle: the obscure "fast" mode was suspected of causing stack
  overflows on the Mac.  Hopefully fixed this by setting the recursion
  limit much smaller.  If the limit is too low (it only affects
  performance), you can change it by defining PY_CPICKLE_FAST_LIMIT
  when compiling cPickle.c (or in pyconfig.h).

Library

- dumbdbm.py: fixed a dumb old bug (the file didn't get synched at
  close or delete time).

- rfc822.py: fixed a bug where the address '<>' was converted to None
  instead of an empty string (also fixes the email.Utils module).

- xmlrpclib.py: version 1.0.0; uses precision for doubles.

- test suite: the pickle and cPickle tests were not executing any code
  when run from the standard regression test.

Tools/Demos

Build

C API

New platforms

Tests

Windows

- distutils package: fixed broken Windows installers (bdist_wininst).

- tempfile.py: prevent mysterious warnings when TemporaryFileWrapper
  instances are deleted at process exit time.

- socket.py: prevent mysterious warnings when socket instances are
  deleted at process exit time.

- posixmodule.c: fix a Windows crash with stat() of a filename ending
  in backslash.

Mac

- The Carbon toolbox modules have been upgraded to Universal Headers
  3.4, and experimental CoreGraphics and CarbonEvents modules have
  been added.  All only for framework-enabled MacOSX.


What's New in Python 2.2c1?
Release date: 14-Dec-2001
===========================

Type/class unification and new-style classes

- Guido's tutorial introduction to the new type/class features has
  been extensively updated.  See

      http://www.python.org/2.2/descrintro.html

  That remains the primary documentation in this area.

- Fixed a leak: instance variables declared with __slots__ were never
  deleted!

- The "delete attribute" method of descriptor objects is called
  __delete__, not __del__.  In previous releases, it was mistakenly
  called __del__, which created an unfortunate overloading condition
  with finalizers.  (The "get attribute" and "set attribute" methods
  are still called __get__ and __set__, respectively.)

- Some subtle issues with the super built-in were fixed:

  (a) When super itself is subclassed, its __get__ method would still
      return an instance of the base class (i.e., of super).

  (b) super(C, C()).__class__ would return C rather than super.  This
      is confusing.  To fix this, I decided to change the semantics of
      super so that it only applies to code attributes, not to data
      attributes.  After all, overriding data attributes is not
      supported anyway.

  (c) The __get__ method didn't check whether the argument was an
      instance of the type used in creation of the super instance.

- Previously, hash() of an instance of a subclass of a mutable type
  (list or dictionary) would return some value, rather than raising
  TypeError.  This has been fixed.  Also, directly calling
  dict.__hash__ and list.__hash__ now raises the same TypeError
  (previously, these were the same as object.__hash__).

- New-style objects now support deleting their __dict__.  This is for
  all intents and purposes equivalent to assigning a brand new empty
  dictionary, but saves space if the object is not used further.

Core and builtins

- -Qnew now works as documented in PEP 238:  when -Qnew is passed on
  the command line, all occurrences of "/" use true division instead
  of classic division.  See the PEP for details.  Note that "all"
  means all instances in library and 3rd-party modules, as well as in
  your own code.  As the PEP says, -Qnew is intended for use only in
  educational environments with control over the libraries in use.
  Note that test_coercion.py in the standard Python test suite fails
  under -Qnew; this is expected, and won't be repaired until true
  division becomes the default (in the meantime, test_coercion is
  testing the current rules).

- complex() now only allows the first argument to be a string
  argument, and raises TypeError if either the second arg is a string
  or if the second arg is specified when the first is a string.

Extension modules

- gc.get_referents was renamed to gc.get_referrers.

Library

- Functions in the os.spawn() family now release the global interpreter
  lock around calling the platform spawn.  They should always have done
  this, but did not before 2.2c1.  Multithreaded programs calling
  an os.spawn function with P_WAIT will no longer block all Python threads
  until the spawned program completes.  It's possible that some programs
  relies on blocking, although more likely by accident than by design.

- webbrowser defaults to netscape.exe on OS/2 now.

- Tix.ResizeHandle exposes detach_widget, hide, and show.

- The charset alias windows_1252 has been added.

- types.StringTypes is a tuple containing the defined string types;
  usually this will be (str, unicode), but if Python was compiled
  without Unicode support it will be just (str,).

- The pulldom and minidom modules were synchronized to PyXML.

Tools/Demos

- A new script called Tools/scripts/google.py was added, which fires
  off a search on Google.

Build

- Note that release builds of Python should arrange to define the
  preprocessor symbol NDEBUG on the command line (or equivalent).
  In the 2.2 pre-release series we tried to define this by magic in
  Python.h instead, but it proved to cause problems for extension
  authors.  The Unix, Windows and Mac builds now all define NDEBUG in
  release builds via cmdline (or equivalent) instead.  Ports to
  other platforms should do likewise.

- It is no longer necessary to use --with-suffix when building on a
  case-insensitive file system (such as Mac OS X HFS+). In the build
  directory an extension is used, but not in the installed python.

C API

- New function PyDict_MergeFromSeq2() exposes the builtin dict
  constructor's logic for updating a dictionary from an iterable object
  producing key-value pairs.

- PyArg_ParseTupleAndKeywords() requires that the number of entries in
  the keyword list equal the number of argument specifiers.  This
  wasn't checked correctly, and PyArg_ParseTupleAndKeywords could even
  dump core in some bad cases.  This has been repaired.  As a result,
  PyArg_ParseTupleAndKeywords may raise RuntimeError in bad cases that
  previously went unchallenged.

New platforms

Tests

Windows

Mac

- In unix-Python on Mac OS X (and darwin) sys.platform is now "darwin",
  without any trailing digits.

- Changed logic for finding python home in Mac OS X framework Pythons.
  Now sys.executable points to the executable again, in stead of to
  the shared library. The latter is used only for locating the python
  home.


What's New in Python 2.2b2?
Release date: 16-Nov-2001
===========================

Type/class unification and new-style classes

- Multiple inheritance mixing new-style and classic classes in the
  list of base classes is now allowed, so this works now:

      class Classic: pass
      class Mixed(Classic, object): pass

  The MRO (method resolution order) for each base class is respected
  according to its kind, but the MRO for the derived class is computed
  using new-style MRO rules if any base class is a new-style class.
  This needs to be documented.

- The new builtin dictionary() constructor, and dictionary type, have
  been renamed to dict.  This reflects a decade of common usage.

- dict() now accepts an iterable object producing 2-sequences.  For
  example, dict(d.items()) == d for any dictionary d.  The argument,
  and the elements of the argument, can be any iterable objects.

- New-style classes can now have a __del__ method, which is called
  when the instance is deleted (just like for classic classes).

- Assignment to object.__dict__ is now possible, for objects that are
  instances of new-style classes that have a __dict__ (unless the base
  class forbids it).

- Methods of built-in types now properly check for keyword arguments
  (formerly these were silently ignored).  The only built-in methods
  that take keyword arguments are __call__, __init__ and __new__.

- The socket function has been converted to a type; see below.

Core and builtins

- Assignment to __debug__ raises SyntaxError at compile-time.  This
  was promised when 2.1c1 was released as "What's New in Python 2.1c1"
  (see below) says.

- Clarified the error messages for unsupported operands to an operator
  (like 1 + '').

Extension modules

- mmap has a new keyword argument, "access", allowing a uniform way for
  both Windows and Unix users to create read-only, write-through and
  copy-on-write memory mappings.  This was previously possible only on
  Unix.  A new keyword argument was required to support this in a
  uniform way because the mmap() signatures had diverged across
  platforms.  Thanks to Jay T Miller for repairing this!

- By default, the gc.garbage list now contains only those instances in
  unreachable cycles that have __del__ methods; in 2.1 it contained all
  instances in unreachable cycles.  "Instances" here has been generalized
  to include instances of both new-style and old-style classes.

- The socket module defines a new method for socket objects,
  sendall().  This is like send() but may make multiple calls to
  send() until all data has been sent.  Also, the socket function has
  been converted to a subclassable type, like list and tuple (etc.)
  before it; socket and SocketType are now the same thing.

- Various bugfixes to the curses module.  There is now a test suite
  for the curses module (you have to run it manually).

- binascii.b2a_base64 no longer places an arbitrary restriction of 57
  bytes on its input.

Library

- tkFileDialog exposes a Directory class and askdirectory
  convenience function.

- Symbolic group names in regular expressions must be unique.  For
  example, the regexp r'(?P<abc>)(?P<abc>)' is not allowed, because a
  single name can't mean both "group 1" and "group 2" simultaneously.
  Python 2.2 detects this error at regexp compilation time;
  previously, the error went undetected, and results were
  unpredictable.  Also in sre, the pattern.split(), pattern.sub(), and
  pattern.subn() methods have been rewritten in C.  Also, an
  experimental function/method finditer() has been added, which works
  like findall() but returns an iterator.

- Tix exposes more commands through the classes DirSelectBox,
  DirSelectDialog, ListNoteBook, Meter, CheckList, and the
  methods tix_addbitmapdir, tix_cget, tix_configure, tix_filedialog,
  tix_getbitmap, tix_getimage, tix_option_get, and tix_resetoptions.

- Traceback objects are now scanned by cyclic garbage collection, so
  cycles created by casual use of sys.exc_info() no longer cause
  permanent memory leaks (provided garbage collection is enabled).

- os.extsep -- a new variable needed by the RISCOS support.  It is the
  separator used by extensions, and is '.' on all platforms except
  RISCOS, where it is '/'.  There is no need to use this variable
  unless you have a masochistic desire to port your code to RISCOS.

- mimetypes.py has optional support for non-standard, but commonly
  found types.  guess_type() and guess_extension() now accept an
  optional `strict' flag, defaulting to true, which controls whether
  recognize non-standard types or not.  A few non-standard types we
  know about have been added.  Also, when run as a script, there are
  new -l and -e options.

- statcache is now deprecated.

- email.Utils.formatdate() now produces the preferred RFC 2822 style
  dates with numeric timezones (it used to produce obsolete dates
  hard coded to "GMT" timezone).  An optional `localtime' flag is
  added to produce dates in the local timezone, with daylight savings
  time properly taken into account.

- In pickle and cPickle, instead of masking errors in load() by
  transforming them into SystemError, we let the original exception
  propagate out.  Also, implement support for __safe_for_unpickling__
  in pickle, as it already was supported in cPickle.

Tools/Demos

Build

- The dbm module is built using libdb1 if available.  The bsddb module
  is built with libdb3 if available.

- Misc/Makefile.pre.in has been removed by BDFL pronouncement.

C API

- New function PySequence_Fast_GET_SIZE() returns the size of a non-
  NULL result from PySequence_Fast(), more quickly than calling
  PySequence_Size().

- New argument unpacking function PyArg_UnpackTuple() added.

- New functions PyObject_CallFunctionObjArgs() and
  PyObject_CallMethodObjArgs() have been added to make it more
  convenient and efficient to call functions and methods from C.

- PyArg_ParseTupleAndKeywords() no longer masks errors, so it's
  possible that this will propagate errors it didn't before.

- New function PyObject_CheckReadBuffer(), which returns true if its
  argument supports the single-segment readable buffer interface.

New platforms

- We've finally confirmed that this release builds on HP-UX 11.00,
  *with* threads, and passes the test suite.

- Thanks to a series of patches from Michael Muller, Python may build
  again under OS/2 Visual Age C++.

- Updated RISCOS port by Dietmar Schwertberger.

Tests

- Added a test script for the curses module.  It isn't run automatically;
  regrtest.py must be run with '-u curses' to enable it.

Windows

Mac

- PythonScript has been moved to unsupported and is slated to be
  removed completely in the next release.

- It should now be possible to build applets that work on both OS9 and
  OSX.

- The core is now linked with CoreServices not Carbon; as a side
  result, default 8bit encoding on OSX is now ASCII.

- Python should now build on OSX 10.1.1


What's New in Python 2.2b1?
Release date: 19-Oct-2001
===========================

Type/class unification and new-style classes

- New-style classes are now always dynamic (except for built-in and
  extension types).  There is no longer a performance penalty, and I
  no longer see another reason to keep this baggage around.  One relic
  remains: the __dict__ of a new-style class is a read-only proxy; you
  must set the class's attribute to modify it.  As a consequence, the
  __defined__ attribute of new-style types no longer exists, for lack
  of need: there is once again only one __dict__ (although in the
  future a __cache__ may be resurrected with a similar function, if I
  can prove that it actually speeds things up).

- C.__doc__ now works as expected for new-style classes (in 2.2a4 it
  always returned None, even when there was a class docstring).

- doctest now finds and runs docstrings attached to new-style classes,
  class methods, static methods, and properties.

Core and builtins

- A very subtle syntactical pitfall in list comprehensions was fixed.
  For example: [a+b for a in 'abc', for b in 'def'].  The comma in
  this example is a mistake.  Previously, this would silently let 'a'
  iterate over the singleton tuple ('abc',), yielding ['abcd', 'abce',
  'abcf'] rather than the intended ['ad', 'ae', 'af', 'bd', 'be',
  'bf', 'cd', 'ce', 'cf'].  Now, this is flagged as a syntax error.
  Note that [a for a in <singleton>] is a convoluted way to say
  [<singleton>] anyway, so it's not like any expressiveness is lost.

- getattr(obj, name, default) now only catches AttributeError, as
  documented, rather than returning the default value for all
  exceptions (which could mask bugs in a __getattr__ hook, for
  example).

- Weak reference objects are now part of the core and offer a C API.
  A bug which could allow a core dump when binary operations involved
  proxy reference has been fixed.  weakref.ReferenceError is now a
  built-in exception.

- unicode(obj) now behaves more like str(obj), accepting arbitrary
  objects, and calling a __unicode__ method if it exists.
  unicode(obj, encoding) and unicode(obj, encoding, errors) still
  require an 8-bit string or character buffer argument.

- isinstance() now allows any object as the first argument and a
  class, a type or something with a __bases__ tuple attribute for the
  second argument.  The second argument may also be a tuple of a
  class, type, or something with __bases__, in which case isinstance()
  will return true if the first argument is an instance of any of the
  things contained in the second argument tuple.  E.g.

  isinstance(x, (A, B))

  returns true if x is an instance of A or B.

Extension modules

- thread.start_new_thread() now returns the thread ID (previously None).

- binascii has now two quopri support functions, a2b_qp and b2a_qp.

- readline now supports setting the startup_hook and the
  pre_event_hook, and adds the add_history() function.

- os and posix supports chroot(), setgroups() and unsetenv() where
  available.  The stat(), fstat(), statvfs() and fstatvfs() functions
  now return "pseudo-sequences" -- the various fields can now be
  accessed as attributes (e.g. os.stat("/").st_mtime) but for
  backwards compatibility they also behave as a fixed-length sequence.
  Some platform-specific fields (e.g. st_rdev) are only accessible as
  attributes.

- time: localtime(), gmtime() and strptime() now return a
  pseudo-sequence similar to the os.stat() return value, with
  attributes like tm_year etc.

- Decompression objects in the zlib module now accept an optional
  second parameter to decompress() that specifies the maximum amount
  of memory to use for the uncompressed data.

- optional SSL support in the socket module now exports OpenSSL
  functions RAND_add(), RAND_egd(), and RAND_status().  These calls
  are useful on platforms like Solaris where OpenSSL does not
  automatically seed its PRNG.  Also, the keyfile and certfile
  arguments to socket.ssl() are now optional.

- posixmodule (and by extension, the os module on POSIX platforms) now
  exports O_LARGEFILE, O_DIRECT, O_DIRECTORY, and O_NOFOLLOW.

Library

- doctest now excludes functions and classes not defined by the module
  being tested, thanks to Tim Hochberg.

- HotShot, a new profiler implemented using a C-based callback, has
  been added.  This substantially reduces the overhead of profiling,
  but it is still quite preliminary.  Support modules and
  documentation will be added in upcoming releases (before 2.2 final).

- profile now produces correct output in situations where an exception
  raised in Python is cleared by C code (e.g. hasattr()).  This used
  to cause wrong output, including spurious claims of recursive
  functions and attribution of time spent to the wrong function.

  The code and documentation for the derived OldProfile and HotProfile
  profiling classes was removed.  The code hasn't worked for years (if
  you tried to use them, they raised exceptions).  OldProfile
  intended to reproduce the behavior of the profiler Python used more
  than 7 years ago, and isn't interesting anymore.  HotProfile intended
  to provide a faster profiler (but producing less information), and
  that's a worthy goal we intend to meet via a different approach (but
  without losing information).

- Profile.calibrate() has a new implementation that should deliver
  a much better system-specific calibration constant.  The constant can
  now be specified in an instance constructor, or as a Profile class or
  instance variable, instead of by editing profile.py's source code.
  Calibration must still be done manually (see the docs for the profile
  module).

  Note that Profile.calibrate() must be overriden by subclasses.
  Improving the accuracy required exploiting detailed knowledge of
  profiler internals; the earlier method abstracted away the details
  and measured a simplified model instead, but consequently computed
  a constant too small by a factor of 2 on some modern machines.

- quopri's encode and decode methods take an optional header parameter,
  which indicates whether output is intended for the header 'Q'
  encoding.

- The SocketServer.ThreadingMixIn class now closes the request after
  finish_request() returns.  (Not when it errors out though.)

- The nntplib module's NNTP.body() method has grown a `file' argument
  to allow saving the message body to a file.

- The email package has added a class email.Parser.HeaderParser which
  only parses headers and does not recurse into the message's body.
  Also, the module/class MIMEAudio has been added for representing
  audio data (contributed by Anthony Baxter).

- ftplib should be able to handle files > 2GB.

- ConfigParser.getboolean() now also interprets TRUE, FALSE, YES, NO,
  ON, and OFF.

- xml.dom.minidom NodeList objects now support the length attribute
  and item() method as required by the DOM specifications.

Tools/Demos

- Demo/dns was removed.  It no longer serves any purpose; a package
  derived from it is now maintained by Anthony Baxter, see
  http://PyDNS.SourceForge.net.

- The freeze tool has been made more robust, and two new options have
  been added: -X and -E.

Build

- configure will use CXX in LINKCC if CXX is used to build main() and
  the system requires to link a C++ main using the C++ compiler.

C API

- The documentation for the tp_compare slot is updated to require that
  the return value must be -1, 0, 1; an arbitrary number <0 or >0 is
  not correct.  This is not yet enforced but will be enforced in
  Python 2.3; even later, we may use -2 to indicate errors and +2 for
  "NotImplemented".  Right now, -1 should be used for an error return.

- PyLong_AsLongLong() now accepts int (as well as long) arguments.
  Consequently, PyArg_ParseTuple's 'L' code also accepts int (as well
  as long) arguments.

- PyThread_start_new_thread() now returns a long int giving the thread
  ID, if one can be calculated; it returns -1 for error, 0 if no
  thread ID is calculated (this is an incompatible change, but only
  the thread module used this API).  This code has only really been
  tested on Linux and Windows; other platforms please beware (and
  report any bugs or strange behavior).

- PyUnicode_FromEncodedObject() no longer accepts Unicode objects as
  input.

New platforms

Tests

Windows

- Installer:  If you install IDLE, and don't disable file-extension
  registration, a new "Edit with IDLE" context (right-click) menu entry
  is created for .py and .pyw files.

- The signal module now supports SIGBREAK on Windows, thanks to Steven
  Scott.  Note that SIGBREAK is unique to Windows.  The default SIGBREAK
  action remains to call Win32 ExitProcess().  This can be changed via
  signal.signal().  For example:

  # Make Ctrl+Break raise KeyboardInterrupt, like Python's default Ctrl+C
  # (SIGINT) behavior.
  import signal
  signal.signal(signal.SIGBREAK,
                signal.default_int_handler)

  try:
      while 1:
          pass
  except KeyboardInterrupt:
      # We get here on Ctrl+C or Ctrl+Break now; if we had not changed
      # SIGBREAK, only on Ctrl+C (and Ctrl+Break would terminate the
      # program without the possibility for any Python-level cleanup).
      print "Clean exit"


What's New in Python 2.2a4?
Release date: 28-Sep-2001
===========================

Type/class unification and new-style classes

- pydoc and inspect are now aware of new-style classes;
  e.g. help(list) at the interactive prompt now shows proper
  documentation for all operations on list objects.

- Applications using Jim Fulton's ExtensionClass module can now safely
  be used with Python 2.2.  In particular, Zope 2.4.1 now works with
  Python 2.2 (as well as with Python 2.1.1).  The Demo/metaclass
  examples also work again.  It is hoped that Gtk and Boost also work
  with 2.2a4 and beyond.  (If you can confirm this, please write
  webmaster@python.org; if there are still problems, please open a bug
  report on SourceForge.)

- property() now takes 4 keyword arguments:  fget, fset, fdel and doc.
  These map to read-only attributes 'fget', 'fset', 'fdel', and '__doc__'
  in the constructed property object.  fget, fset and fdel weren't
  discoverable from Python in 2.2a3.  __doc__ is new, and allows to
  associate a docstring with a property.

- Comparison overloading is now more completely implemented.  For
  example, a str subclass instance can properly be compared to a str
  instance, and it can properly overload comparison.  Ditto for most
  other built-in object types.

- The repr() of new-style classes has changed; instead of <type
  'M.Foo'> a new-style class is now rendered as <class 'M.Foo'>,
  *except* for built-in types, which are still rendered as <type
  'Foo'> (to avoid upsetting existing code that might parse or
  otherwise rely on repr() of certain type objects).

- The repr() of new-style objects is now always <Foo object at XXX>;
  previously, it was sometimes <Foo instance at XXX>.

- For new-style classes, what was previously called __getattr__ is now
  called __getattribute__.  This method, if defined, is called for
  *every* attribute access.  A new __getattr__ hook more similar to the
  one in classic classes is defined which is called only if regular
  attribute access raises AttributeError; to catch *all* attribute
  access, you can use __getattribute__ (for new-style classes).  If
  both are defined, __getattribute__ is called first, and if it raises
  AttributeError, __getattr__ is called.

- The __class__ attribute of new-style objects can be assigned to.
  The new class must have the same C-level object layout as the old
  class.

- The builtin file type can be subclassed now.  In the usual pattern,
  "file" is the name of the builtin type, and file() is a new builtin
  constructor, with the same signature as the builtin open() function.
  file() is now the preferred way to open a file.

- Previously, __new__ would only see sequential arguments passed to
  the type in a constructor call; __init__ would see both sequential
  and keyword arguments.  This made no sense whatsoever any more, so
  now both __new__ and __init__ see all arguments.

- Previously, hash() applied to an instance of a subclass of str or
  unicode always returned 0.  This has been repaired.

- Previously, an operation on an instance of a subclass of an
  immutable type (int, long, float, complex, tuple, str, unicode),
  where the subtype didn't override the operation (and so the
  operation was handled by the builtin type), could return that
  instance instead a value of the base type.  For example, if s was of
  a str subclass type, s[:] returned s as-is.  Now it returns a str
  with the same value as s.

- Provisional support for pickling new-style objects has been added.

Core

- file.writelines() now accepts any iterable object producing strings.

- PyUnicode_FromEncodedObject() now works very much like
  PyObject_Str(obj) in that it tries to use __str__/tp_str
  on the object if the object is not a string or buffer. This
  makes unicode() behave like str() when applied to non-string/buffer
  objects.

- PyFile_WriteObject now passes Unicode objects to the file's write
  method. As a result, all file-like objects which may be the target
  of a print statement must support Unicode objects, i.e. they must
  at least convert them into ASCII strings.

- Thread scheduling on Solaris should be improved; it is no longer
  necessary to insert a small sleep at the start of a thread in order
  to let other runnable threads be scheduled.

Library

- StringIO.StringIO instances and cStringIO.StringIO instances support
  read character buffer compatible objects for their .write() methods.
  These objects are converted to strings and then handled as such
  by the instances.

- The "email" package has been added.  This is basically a port of the
  mimelib package <http://sf.net/projects/mimelib> with API changes
  and some implementations updated to use iterators and generators.

- difflib.ndiff() and difflib.Differ.compare() are generators now.  This
  restores the ability of Tools/scripts/ndiff.py to start producing output
  before the entire comparison is complete.

- StringIO.StringIO instances and cStringIO.StringIO instances support
  iteration just like file objects (i.e. their .readline() method is
  called for each iteration until it returns an empty string).

- The codecs module has grown four new helper APIs to access
  builtin codecs: getencoder(), getdecoder(), getreader(),
  getwriter().

- SimpleXMLRPCServer: a new module (based upon SimpleHTMLServer)
  simplifies writing XML RPC servers.

- os.path.realpath(): a new function that returns the absolute pathname
  after interpretation of symbolic links.  On non-Unix systems, this
  is an alias for os.path.abspath().

- operator.indexOf() (PySequence_Index() in the C API) now works with any
  iterable object.

- smtplib now supports various authentication and security features of
  the SMTP protocol through the new login() and starttls() methods.

- hmac: a new module implementing keyed hashing for message
  authentication.

- mimetypes now recognizes more extensions and file types.  At the
  same time, some mappings not sanctioned by IANA were removed.

- The "compiler" package has been brought up to date to the state of
  Python 2.2 bytecode generation.  It has also been promoted from a
  Tool to a standard library package.  (Tools/compiler still exists as
  a sample driver.)

Tools

Build

- Large file support (LFS) is now automatic when the platform supports
  it; no more manual configuration tweaks are needed.  On Linux, at
  least, it's possible to have a system whose C library supports large
  files but whose kernel doesn't; in this case, large file support is
  still enabled but doesn't do you any good unless you upgrade your
  kernel or share your Python executable with another system whose
  kernel has large file support.

- The configure script now supplies plausible defaults in a
  cross-compilation environment.  This doesn't mean that the supplied
  values are always correct, or that cross-compilation now works
  flawlessly -- but it's a first step (and it shuts up most of
  autoconf's warnings about AC_TRY_RUN).

- The Unix build is now a bit less chatty, courtesy of the parser
  generator.  The build is completely silent (except for errors) when
  using "make -s", thanks to a -q option to setup.py.

C API

- The "structmember" API now supports some new flag bits to deny read
  and/or write access to attributes in restricted execution mode.

New platforms

- Compaq's iPAQ handheld, running the "familiar" Linux distribution
  (http://familiar.handhelds.org).

Tests

- The "classic" standard tests, which work by comparing stdout to
  an expected-output file under Lib/test/output/, no longer stop at
  the first mismatch.  Instead the test is run to completion, and a
  variant of ndiff-style comparison is used to report all differences.
  This is much easier to understand than the previous style of reporting.

- The unittest-based standard tests now use regrtest's test_main()
  convention, instead of running as a side-effect of merely being
  imported.  This allows these tests to be run in more natural and
  flexible ways as unittests, outside the regrtest framework.

- regrtest.py is much better integrated with unittest and doctest now,
  especially in regard to reporting errors.

Windows

- Large file support now also works for files > 4GB, on filesystems
  that support it (NTFS under Windows 2000).  See "What's New in
  Python 2.2a3" for more detail.


What's New in Python 2.2a3?
Release Date: 07-Sep-2001
===========================

Core

- Conversion of long to float now raises OverflowError if the long is too
  big to represent as a C double.

- The 3-argument builtin pow() no longer allows a third non-None argument
  if either of the first two arguments is a float, or if both are of
  integer types and the second argument is negative (in which latter case
  the arguments are converted to float, so this is really the same
  restriction).

- The builtin dir() now returns more information, and sometimes much
  more, generally naming all attributes of an object, and all attributes
  reachable from the object via its class, and from its class's base
  classes, and so on from them too.  Example:  in 2.2a2, dir([]) returned
  an empty list.  In 2.2a3,

  >>> dir([])
  ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__',
   '__eq__', '__ge__', '__getattr__', '__getitem__', '__getslice__',
   '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__le__',
   '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__repr__',
   '__rmul__', '__setattr__', '__setitem__', '__setslice__', '__str__',
   'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove',
   'reverse', 'sort']

  dir(module) continues to return only the module's attributes, though.

- Overflowing operations on plain ints now return a long int rather
  than raising OverflowError.  This is a partial implementation of PEP
  237.  You can use -Wdefault::OverflowWarning to enable a warning for
  this situation, and -Werror::OverflowWarning to revert to the old
  OverflowError exception.

- A new command line option, -Q<arg>, is added to control run-time
  warnings for the use of classic division.  (See PEP 238.)  Possible
  values are -Qold, -Qwarn, -Qwarnall, and -Qnew.  The default is
  -Qold, meaning the / operator has its classic meaning and no
  warnings are issued.  Using -Qwarn issues a run-time warning about
  all uses of classic division for int and long arguments; -Qwarnall
  also warns about classic division for float and complex arguments
  (for use with fixdiv.py).
  [Note:  the remainder of this paragraph (preserved below) became
   obsolete in 2.2c1 -- -Qnew has global effect in 2.2]
  <obsolete>
  Using -Qnew is questionable; it turns on new division by default, but
  only in the __main__ module.  You can usefully combine -Qwarn or
  -Qwarnall and -Qnew: this gives the __main__ module new division, and
  warns about classic division everywhere else.
  </obsolete>

- Many built-in types can now be subclassed.  This applies to int,
  long, float, str, unicode, and tuple.  (The types complex, list and
  dictionary can also be subclassed; this was introduced earlier.)
  Note that restrictions apply when subclassing immutable built-in
  types: you can only affect the value of the instance by overloading
  __new__.  You can add mutable attributes, and the subclass instances
  will have a __dict__ attribute, but you cannot change the "value"
  (as implemented by the base class) of an immutable subclass instance
  once it is created.

- The dictionary constructor now takes an optional argument, a
  mapping-like object, and initializes the dictionary from its
  (key, value) pairs.

- A new built-in type, super, has been added.  This facilitates making
  "cooperative super calls" in a multiple inheritance setting.  For an
  explanation, see http://www.python.org/2.2/descrintro.html#cooperation

- A new built-in type, property, has been added.  This enables the
  creation of "properties".  These are attributes implemented by
  getter and setter functions (or only one of these for read-only or
  write-only attributes), without the need to override __getattr__.
  See http://www.python.org/2.2/descrintro.html#property

- The syntax of floating-point and imaginary literals has been
  liberalized, to allow leading zeroes.  Examples of literals now
  legal that were SyntaxErrors before:

      00.0    0e3   0100j   07.5   00000000000000000008.

- An old tokenizer bug allowed floating point literals with an incomplete
  exponent, such as 1e and 3.1e-.  Such literals now raise SyntaxError.

Library

- telnetlib includes symbolic names for the options, and support for
  setting an option negotiation callback.

- The new C standard no longer requires that math libraries set errno to
  ERANGE on overflow.  For platform libraries that exploit this new
  freedom, Python's overflow-checking was wholly broken.  A new overflow-
  checking scheme attempts to repair that, but may not be reliable on all
  platforms (C doesn't seem to provide anything both useful and portable
  in this area anymore).

- Asynchronous timeout actions are available through the new class
  threading.Timer.

- math.log and math.log10 now return sensible results for even huge
  long arguments.  For example, math.log10(10 ** 10000) ~= 10000.0.

- A new function, imp.lock_held(), returns 1 when the import lock is
  currently held.  See the docs for the imp module.

- pickle, cPickle and marshal on 32-bit platforms can now correctly read
  dumps containing ints written on platforms where Python ints are 8 bytes.
  When read on a box where Python ints are 4 bytes, such values are
  converted to Python longs.

- In restricted execution mode (using the rexec module), unmarshalling
  code objects is no longer allowed.  This plugs a security hole.

- unittest.TestResult instances no longer store references to tracebacks
  generated by test failures. This prevents unexpected dangling references
  to objects that should be garbage collected between tests.

Tools

- Tools/scripts/fixdiv.py has been added which can be used to fix
  division operators as per PEP 238.

Build

- If you are an adventurous person using Mac OS X you may want to look at
  Mac/OSX. There is a Makefile there that will build Python as a real Mac
  application, which can be used for experimenting with Carbon or Cocoa.
  Discussion of this on pythonmac-sig, please.

C API

- New function PyObject_Dir(obj), like Python __builtin__.dir(obj).

- Note that PyLong_AsDouble can fail!  This has always been true, but no
  callers checked for it.  It's more likely to fail now, because overflow
  errors are properly detected now.  The proper way to check:

  double x = PyLong_AsDouble(some_long_object);
  if (x == -1.0 && PyErr_Occurred()) {
          /* The conversion failed. */
  }

- The GC API has been changed.  Extensions that use the old API will still
  compile but will not participate in GC.  To upgrade an extension
  module:

    - rename Py_TPFLAGS_GC to PyTPFLAGS_HAVE_GC

    - use PyObject_GC_New or PyObject_GC_NewVar to allocate objects and
      PyObject_GC_Del to deallocate them

    - rename PyObject_GC_Init to PyObject_GC_Track and PyObject_GC_Fini
      to PyObject_GC_UnTrack

    - remove PyGC_HEAD_SIZE from object size calculations

    - remove calls to PyObject_AS_GC and PyObject_FROM_GC

- Two new functions: PyString_FromFormat() and PyString_FromFormatV().
  These can be used safely to construct string objects from a
  sprintf-style format string (similar to the format string supported
  by PyErr_Format()).

New platforms

- Stephen Hansen contributed patches sufficient to get a clean compile
  under Borland C (Windows), but he reports problems running it and ran
  out of time to complete the port.  Volunteers?  Expect a MemoryError
  when importing the types module; this is probably shallow, and
  causing later failures too.

Tests

Windows

- Large file support is now enabled on Win32 platforms as well as on
  Win64.  This means that, for example, you can use f.tell() and f.seek()
  to manipulate files larger than 2 gigabytes (provided you have enough
  disk space, and are using a Windows filesystem that supports large
  partitions).  Windows filesystem limits:  FAT has a 2GB (gigabyte)
  filesize limit, and large file support makes no difference there.
  FAT32's limit is 4GB, and files >= 2GB are easier to use from Python now.
  NTFS has no practical limit on file size, and files of any size can be
  used from Python now.

- The w9xpopen hack is now used on Windows NT and 2000 too when COMPSPEC
  points to command.com (patch from Brian Quinlan).


What's New in Python 2.2a2?
Release Date: 22-Aug-2001
===========================

Build

- Tim Peters developed a brand new Windows installer using Wise 8.1,
  generously donated to us by Wise Solutions.

- configure supports a new option --enable-unicode, with the values
  ucs2 and ucs4 (new in 2.2a1). With --disable-unicode, the Unicode
  type and supporting code is completely removed from the interpreter.

- A new configure option --enable-framework builds a Mac OS X framework,
  which "make frameworkinstall" will install. This provides a starting
  point for more mac-like functionality, join pythonmac-sig@python.org
  if you are interested in helping.

- The NeXT platform is no longer supported.

- The `new' module is now statically linked.

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.  regrtest
  also has optional --use/-u switch to run normally disabled tests
  which require network access or consume significant disk resources.

- Several new tests in the standard test suite, with special thanks to
  Nick Mathewson.

Core

- The floor division operator // has been added as outlined in PEP
  238.  The / operator still provides classic division (and will until
  Python 3.0) unless "from __future__ import division" is included, in
  which case the / operator will provide true division.  The operator
  module provides truediv() and floordiv() functions.  Augmented
  assignment variants are included, as are the equivalent overloadable
  methods and C API methods.  See the PEP for a full discussion:
  <http://python.sf.net/peps/pep-0238.html>

- Future statements are now effective in simulated interactive shells
  (like IDLE).  This should "just work" by magic, but read Michael
  Hudson's "Future statements in simulated shells" PEP 264 for full
  details:  <http://python.sf.net/peps/pep-0264.html>.

- The type/class unification (PEP 252-253) was integrated into the
  trunk and is not so tentative any more (the exact specification of
  some features is still tentative).  A lot of work has done on fixing
  bugs and adding robustness and features (performance still has to
  come a long way).

- 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.

- A new command line option, -E, was added which disables the use of
  all environment variables, or at least those that are specifically
  significant to Python.  Usually those have a name starting with
  "PYTHON".  This was used to fix a problem where the tests fail if
  the user happens to have PYTHONHOME or PYTHONPATH pointing to an
  older distribution.

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.

- Calling os.tempnam() or os.tmpnam() generate RuntimeWarnings.

- Added function threading.BoundedSemaphore()

- Added Ka-Ping Yee's cgitb.py module.

- The `new' module now exposes the CO_xxx flags.

- The gc module offers the get_referents function.

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.

- Two new flags METH_NOARGS and METH_O are available in method definition
  tables to simplify implementation of methods with no arguments and a
  single untyped argument. Calling such methods is more efficient than
  calling corresponding METH_VARARGS methods. METH_OLDARGS is now
  deprecated.

Windows

- "import module" now compiles module.pyw if it exists and nothing else
  relevant is found.


What's New in Python 2.2a1?
Release date: 18-Jul-2001
===========================

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
  incompatibilities 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-independent
  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 mutate 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 verifies that pprint.isrecursive() and
  pprint.isreadable() return sensible results.  Also verifies that simple
  cases produce correct output.

C API

- Removed the unused last_is_sticky argument from the internal
  _PyTuple_Resize().  If this affects you, you were cheating.


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


What's New in Python 2.1 (final)?
=================================

We only changed a few things since the last release candidate, all in
Python library code:

- A bug in the locale module was fixed that affected locales which
  define no grouping for numeric formatting.

- A few bugs in the weakref module's implementations of weak
  dictionaries (WeakValueDictionary and WeakKeyDictionary) were fixed,
  and the test suite was updated to check for these bugs.

- An old bug in the os.path.walk() function (introduced in Python
  2.0!) was fixed: a non-existent file would cause an exception
  instead of being ignored.

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


What's New in Python 2.1c2?
===========================

A flurry of small changes, and one showstopper fixed in the nick of
time made it necessary to release another release candidate.  The list
here is the *complete* list of patches (except version updates):

Core

- Tim discovered a nasty bug in the dictionary code, caused by
  PyDict_Next() calling dict_resize(), and the GC code's use of
  PyDict_Next() violating an assumption in dict_items().  This was
  fixed with considerable amounts of band-aid, but the net effect is a
  saner and more robust implementation.

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

Build and Ports

- The setup.py script didn't check for a new enough version of zlib
  (1.1.3 is needed).  Now it does.

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

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

Library

- Fix a bug in urllib.basejoin("http://host", "../file.html") which
  omitted the slash between host and file.html.

- The mailbox module's _Mailbox class contained a completely broken
  and undocumented seek() method.  Ripped it out.

- Fixed a bunch of typos in various library modules (urllib2, smtpd,
  sgmllib, netrc, chunk) found by Neil Norwitz's PyChecker.

- Fixed a few last-minute bugs in unittest.

Extensions

- Reverted the patch to the OpenSSL code in socketmodule.c to support
  RAND_status() and the EGD, and the subsequent patch that tried to
  fix it for pre-0.9.5 versions; the problem with the patch is that on
  some systems it issues a warning whenever socket is imported, and
  that's unacceptable.

Tests

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

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

- In distutils/archive_util.py, call zipfile.ZipFile() with mode "w",
  not "wb" (which is not a valid mode at all).

- Fix pstats browser crashes.  Import readline if it exists to make
  the user interface nicer.

- Add "import thread" to the top of test modules that import the
  threading module (test_asynchat and test_threadedtempfile).  This
  prevents test failures caused by a broken threading module resulting
  from a previously caught failed import.

- Changed test_asynchat.py to set the SO_REUSEADDR option; this was
  needed on some platforms (e.g. Solaris 8) when the tests are run
  twice in succession.

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


What's New in Python 2.1c1?
===========================

This list was significantly updated when 2.1c2 was released; the 2.1c1
release didn't mention most changes that were actually part of 2.1c1:

Legal

- Copyright was assigned to the Python Software Foundation (PSF) and a
  PSF license (very similar to the CNRI license) was added.

- The CNRI copyright notice was updated to include 2001.

Core

- After a public outcry, assignment to __debug__ is no longer illegal;
  instead, a warning is issued.  It will become illegal in 2.2.

- Fixed a core dump with "%#x" % 0, and changed the semantics so that
  "%#x" now always prepends "0x", even if the value is zero.

- Fixed some nits in the bytecode compiler.

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

- Fixed various core dumps caused by reference count bugs.

Build and Ports

- Use INSTALL_SCRIPT to install script files.

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

- Updated RISCOS port.

- Updated BeOS port and notes.

- Various other porting problems resolved.

Library

- The TERMIOS and SOCKET modules are now truly obsolete and
  unnecessary.  Their symbols are incorporated in the termios and
  socket modules.

- Fixed some 64-bit bugs in pickle, cPickle, and struct, and added
  better tests for pickling.

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

- zipfile: add support to zipfile to support opening an archive
  represented by an open file rather than a file name.  Fix bug where
  the archive was not properly closed.  Fixed a bug in this bugfix
  where flush() was called for a read-only file.

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

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

- SocketServer: API change (added overridable close_request() method)
  so that the TCP server can explicitly close the request.

- pstats: Eric Raymond added a simple interactive statistics browser,
  invoked when the module is run as a script.

- locale: fixed a problem in format().

- webbrowser: made it work when the BROWSER environment variable has a
  value like "/usr/bin/netscape".  Made it auto-detect Konqueror for
  KDE 2.  Fixed some other nits.

- unittest: changes to allow using a different exception than
  AssertionError, and added a few more function aliases.  Some other
  small changes.

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

- asynchat: fixed a critical bug in asynchat that slipped through the
  2.1b2 release.  Fixed another rare bug.

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

XML

- pyexpat: new API get_version_string().

- Fixed some minidom bugs.

Extensions

- Fixed a core dump in _weakref.  Removed the weakref.mapping()
  function (it adds nothing to the API).

- Rationalized the use of header files in the readline module, to make
  it compile (albeit with some warnings) with the very recent readline
  4.2, without breaking for earlier versions.

- Hopefully fixed a buffering problem in linuxaudiodev.

- Attempted a fix to make the OpenSSL support in the socket module
  work again with pre-0.9.5 versions of OpenSSL.

Tests

- Added a test case for asynchat and asyncore.

- Removed coupling between tests where one test failing could break
  another.

Tools

- Ping added an interactive help browser to pydoc, fixed some nits
  in the rest of the pydoc code, and added some features to his
  inspect module.

- An updated python-mode.el version 4.1 which integrates Ken
  Manheimer's pdbtrack.el.  This makes debugging Python code via pdb
  much nicer in XEmacs and Emacs.  When stepping through your program
  with pdb, in either the shell window or the *Python* window, the
  source file and line will be tracked by an arrow.  Very cool!

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

- Some improvements to Tools/webchecker (ignore some more URL types,
  follow some more links).

- Brought the Tools/compiler package up to date.


What's New in Python 2.1 beta 2?
================================

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

Core language, builtins, and interpreter

- The nested scopes work (enabled by "from __future__ import
  nested_scopes") is completed; in particular, the future now extends
  into code executed through exec, eval() and execfile(), and into the
  interactive interpreter.

- When calling a base class method (e.g. BaseClass.__init__(self)),
  this is now allowed even if self is not strictly spoken a class
  instance (e.g. when using metaclasses or the Don Beaudry hook).

- Slice objects are now comparable but not hashable; this prevents
  dict[:] from being accepted but meaningless.

- Complex division is now calculated using less braindead algorithms.
  This doesn't change semantics except it's more likely to give useful
  results in extreme cases.  Complex repr() now uses full precision
  like float repr().

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

- It is illegal to assign to the name __debug__, which is set when the
  interpreter starts.  It is effectively a compile-time constant.

- A warning will be issued if a global statement for a variable
  follows a use or assignment of that variable.

Standard library

- unittest.py, a unit testing framework by Steve Purcell (PyUNIT,
  inspired by JUnit), is now part of the standard library.  You now
  have a choice of two testing frameworks: unittest requires you to
  write testcases as separate code, doctest gathers them from
  docstrings.  Both approaches have their advantages and
  disadvantages.

- A new module Tix was added, which wraps the Tix extension library
  for Tk.  With that module, it is not necessary to statically link
  Tix with _tkinter, since Tix will be loaded with Tcl's "package
  require" command.  See Demo/tix/.

- tzparse.py is now obsolete.

- In gzip.py, the seek() and tell() methods are removed -- they were
  non-functional anyway, and it's better if callers can test for their
  existence with hasattr().

Python/C API

- PyDict_Next(): it is now safe to call PyDict_SetItem() with a key
  that's already in the dictionary during a PyDict_Next() iteration.
  This used to fail occasionally when a dictionary resize operation
  could be triggered that would rehash all the keys.  All other
  modifications to the dictionary are still off-limits during a
  PyDict_Next() iteration!

- New extended APIs related to passing compiler variables around.

- New abstract APIs PyObject_IsInstance(), PyObject_IsSubclass()
  implement isinstance() and issubclass().

- Py_BuildValue() now has a "D" conversion to create a Python complex
  number from a Py_complex C value.

- Extensions types which support weak references must now set the
  field allocated for the weak reference machinery to NULL themselves;
  this is done to avoid the cost of checking each object for having a
  weakly referencable type in PyObject_INIT(), since most types are
  not weakly referencable.

- PyFrame_FastToLocals() and PyFrame_LocalsToFast() copy bindings for
  free variables and cell variables to and from the frame's f_locals.

- Variants of several functions defined in pythonrun.h have been added
  to support the nested_scopes future statement.  The variants all end
  in Flags and take an extra argument, a PyCompilerFlags *; examples:
  PyRun_AnyFileExFlags(), PyRun_InteractiveLoopFlags().  These
  variants may be removed in Python 2.2, when nested scopes are
  mandatory.

Distutils

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

- several enhancements to the bdist_wininst command from Thomas Heller
  (an uninstaller, more customization of the installer's display)

- from Jack Jansen: added Mac-specific code to generate a dialog for
  users to specify the command-line (because providing a command-line with
  MacPython is awkward).  Jack also made various fixes for the Mac
  and the Metrowerks compiler.

- added 'platforms' and 'keywords' to the set of metadata that can be
  specified for a distribution.

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


What's New in Python 2.1 beta 1?
================================

Core language, builtins, and interpreter

- Following an outcry from the community about the amount of code
  broken by the nested scopes feature introduced in 2.1a2, we decided
  to make this feature optional, and to wait until Python 2.2 (or at
  least 6 months) to make it standard.  The option can be enabled on a
  per-module basis by adding "from __future__ import nested_scopes" at
  the beginning of a module (before any other statements, but after
  comments and an optional docstring).  See PEP 236 (Back to the
  __future__) for a description of the __future__ statement.  PEP 227
  (Statically Nested Scopes) has been updated to reflect this change,
  and to clarify the semantics in a number of endcases.

- The nested scopes code, when enabled, has been hardened, and most
  bugs and memory leaks in it have been fixed.

- Compile-time warnings are now generated for a number of conditions
  that will break or change in meaning when nested scopes are enabled:

  - Using "from...import *" or "exec" without in-clause in a function
    scope that also defines a lambda or nested function with one or
    more free (non-local) variables.  The presence of the import* or
    bare exec makes it impossible for the compiler to determine the
    exact set of local variables in the outer scope, which makes it
    impossible to determine the bindings for free variables in the
    inner scope.  To avoid the warning about import *, change it into
    an import of explicitly name object, or move the import* statement
    to the global scope; to avoid the warning about bare exec, use
    exec...in... (a good idea anyway -- there's a possibility that
    bare exec will be deprecated in the future).

  - Use of a global variable in a nested scope with the same name as a
    local variable in a surrounding scope.  This will change in
    meaning with nested scopes: the name in the inner scope will
    reference the variable in the outer scope rather than the global
    of the same name.  To avoid the warning, either rename the outer
    variable, or use a global statement in the inner function.

- An optional object allocator has been included.  This allocator is
  optimized for Python objects and should be faster and use less memory
  than the standard system allocator.  It is not enabled by default
  because of possible thread safety problems.  The allocator is only
  protected by the Python interpreter lock and it is possible that some
  extension modules require a thread safe allocator.  The object
  allocator can be enabled by providing the "--with-pymalloc" option to
  configure.

Standard library

- pyexpat now detects the expat version if expat.h defines it. A
  number of additional handlers are provided, which are only available
  since expat 1.95. In addition, the methods SetParamEntityParsing and
  GetInputContext of Parser objects are available with 1.95.x
  only. Parser objects now provide the ordered_attributes and
  specified_attributes attributes. A new module expat.model was added,
  which offers a number of additional constants if 1.95.x is used.

- xml.dom offers the new functions registerDOMImplementation and
  getDOMImplementation.

- xml.dom.minidom offers a toprettyxml method. A number of DOM
  conformance issues have been resolved. In particular, Element now
  has an hasAttributes method, and the handling of namespaces was
  improved.

- Ka-Ping Yee contributed two new modules: inspect.py, a module for
  getting information about live Python code, and pydoc.py, a module
  for interactively converting docstrings to HTML or text.
  Tools/scripts/pydoc, which is now automatically installed into
  <prefix>/bin, uses pydoc.py to display documentation; try running
  "pydoc -h" for instructions.  "pydoc -g" pops up a small GUI that
  lets you browse the module docstrings using a web browser.

- New library module difflib.py, primarily packaging the SequenceMatcher
  class at the heart of the popular ndiff.py file-comparison tool.

- doctest.py (a framework for verifying Python code examples in docstrings)
  is now part of the std library.

Windows changes

- A new entry in the Start menu, "Module Docs", runs "pydoc -g" -- a
  small GUI that lets you browse the module docstrings using your
  default web browser.

- Import is now case-sensitive.  PEP 235 (Import on Case-Insensitive
  Platforms) is implemented.  See

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

  for full details, especially the "Current Lower-Left Semantics" section.
  The new Windows import rules are simpler than before:

  A. If the PYTHONCASEOK environment variable exists, same as
     before:  silently accept the first case-insensitive match of any
     kind; raise ImportError if none found.

  B. Else search sys.path for the first case-sensitive match; raise
     ImportError if none found.

  The same rules have been implemented 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.


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 "(?<!abc)(def)".

- Several bugs in the Unicode handling and error handling in _tkinter
  were fixed.

- Fix memory management errors in Merge() and Tkapp_Call() routines.

- Several changes were made to cStringIO to make it compatible with
  the file-like object interface and with StringIO.  If operations are
  performed on a closed object, an exception is raised.  The truncate
  method now accepts a position argument and readline accepts a size
  argument.

- There were many changes made to the linuxaudiodev module and its
  test suite; as a result, a short, unexpected audio sample should now
  play when the regression test is run.

  Note that this module is named poorly, because it should work
  correctly on any platform that supports the Open Sound System
  (OSS).

  The module now raises exceptions when errors occur instead of
  crashing.  It also defines the AFMT_A_LAW format (logarithmic A-law
  audio) and defines a getptr() method that calls the
  SNDCTL_DSP_GETxPTR ioctl defined in the OSS Programmer's Guide.

- The library_version attribute, introduced in an earlier beta, was
  removed because it can not be supported with early versions of the C
  readline library, which provides no way to determine the version at
  compile-time.

- The binascii module is now enabled on Win64.

- tokenize.py no longer suffers "recursion depth" errors when parsing
  programs with very long string literals.

Internals

- Fixed several buffer overflow vulnerabilities in calculate_path(),
  which is called when the interpreter starts up to determine where
  the standard library is installed.  These vulnerabilities affect all
  previous versions of Python and can be exploited by setting very
  long values for PYTHONHOME or argv[0].  The risk is greatest for a
  setuid Python script, although use of the wrapper in
  Misc/setuid-prog.c will eliminate the vulnerability.

- Fixed garbage collection bugs in instance creation that were
  triggered when errors occurred during initialization.  The solution,
  applied in cPickle and in PyInstance_New(), is to call
  PyObject_GC_Init() after the initialization of the object's
  container attributes is complete.

- pyexpat adds definitions of PyModule_AddStringConstant and
  PyModule_AddObject if the Python version is less than 2.0, which
  provides compatibility with PyXML on Python 1.5.2.

- If the platform has a bogus definition for LONG_BIT (the number of
  bits in a long), an error will be reported at compile time.

- Fix bugs in _PyTuple_Resize() which caused hard-to-interpret garbage
  collection crashes and possibly other, unreported crashes.

- Fixed a memory leak in _PyUnicode_Fini().

Build issues

- configure now accepts a --with-suffix option that specifies the
  executable suffix.  This is useful for builds on Cygwin and Mac OS
  X, for example.

- The mmap.PAGESIZE constant is now initialized using sysconf when
  possible, which eliminates a dependency on -lucb for Reliant UNIX.

- The md5 file should now compile on all platforms.

- The select module now compiles on platforms that do not define
  POLLRDNORM and related constants.

- Darwin (Mac OS X):  Initial support for static builds on this
  platform.

- BeOS: A number of changes were made to the build and installation
  process.  ar-fake now operates on a directory of object files.
  dl_export.h is gone, and its macros now appear on the mwcc command
  line during build on PPC BeOS.

- Platform directory in lib/python2.0 is "plat-beos5" (or
  "plat-beos4", if building on BeOS 4.5), rather than "plat-beos".

- Cygwin: Support for shared libraries, Tkinter, and sockets.

- SunOS 4.1.4_JL: Fix test for directory existence in configure.

Tools and other miscellany

- Removed debugging prints from main used with freeze.

- IDLE auto-indent no longer crashes when it encounters Unicode
  characters.

What's new in 2.0 beta 2 (since beta 1)?
========================================

Core language, builtins, and interpreter

- Add support for unbounded ints in %d,i,u,x,X,o formats; for example
  "%d" % 2L**64 == "18446744073709551616".

- Add -h and -V command line options to print the usage message and
  Python version number and exit immediately.

- eval() and exec accept Unicode objects as code parameters.

- getattr() and setattr() now also accept Unicode objects for the
  attribute name, which are converted to strings using the default
  encoding before lookup.

- Multiplication on string and Unicode now does proper bounds
  checking; e.g. 'a' * 65536 * 65536 will raise ValueError, "repeated
  string is too long."

- Better error message when continue is found in try statement in a
  loop.


Standard library and extensions

- socket module: the OpenSSL code now adds support for RAND_status()
  and EGD (Entropy Gathering Device).

- array: reverse() method of array now works.  buffer_info() now does
  argument checking; it still takes no arguments.

- asyncore/asynchat: Included most recent version from Sam Rushing.

- cgi: Accept '&' or ';' as separator characters when parsing form data.

- CGIHTTPServer: Now works on Windows (and perhaps even Mac).

- ConfigParser: When reading the file, options spelled in upper case
  letters are now correctly converted to lowercase.

- copy: Copy Unicode objects atomically.

- cPickle: Fail gracefully when copy_reg can't be imported.

- cStringIO: Implemented readlines() method.

- dbm: Add get() and setdefault() methods to dbm object.  Add constant
  `library' to module that names the library used.  Added doc strings
  and method names to error messages.  Uses configure to determine
  which ndbm.h file to include; Berkeley DB's nbdm and GDBM's ndbm is
  now available options.

- distutils: Update to version 0.9.3.

- dl: Add several dl.RTLD_ constants.

- fpectl: Now supported on FreeBSD.

- gc: Add DEBUG_SAVEALL option.  When enabled all garbage objects
  found by the collector will be saved in gc.garbage.  This is useful
  for debugging a program that creates reference cycles.

- httplib: Three changes: Restore support for set_debuglevel feature
  of HTTP class.  Do not close socket on zero-length response.  Do not
  crash when server sends invalid content-length header.

- mailbox: Mailbox class conforms better to qmail specifications.

- marshal: When reading a short, sign-extend on platforms where shorts
  are bigger than 16 bits.  When reading a long, repair the unportable
  sign extension that was being done for 64-bit machines.  (It assumed
  that signed right shift sign-extends.)

- operator: Add contains(), invert(), __invert__() as aliases for
  __contains__(), inv(), and __inv__() respectively.

- os: Add support for popen2() and popen3() on all platforms where
  fork() exists.  (popen4() is still in the works.)

- os: (Windows only:) Add startfile() function that acts like double-
  clicking on a file in Explorer (or passing the file name to the
  DOS "start" command).

- os.path: (Windows, DOS:) Treat trailing colon correctly in
  os.path.join.  os.path.join("a:", "b") yields "a:b".

- pickle: Now raises ValueError when an invalid pickle that contains
  a non-string repr where a string repr was expected.  This behavior
  matches cPickle.

- posixfile: Remove broken __del__() method.

- py_compile: support CR+LF line terminators in source file.

- readline: Does not immediately exit when ^C is hit when readline and
  threads are configured.  Adds definition of rl_library_version.  (The
  latter addition requires GNU readline 2.2 or later.)

- rfc822: Domain literals returned by AddrlistClass method
  getdomainliteral() are now properly wrapped in brackets.

- site: sys.setdefaultencoding() should only be called in case the
  standard default encoding ("ascii") is changed. This saves quite a
  few cycles during startup since the first call to
  setdefaultencoding() will initialize the codec registry and the
  encodings package.

- socket: Support for size hint in readlines() method of object returned
  by makefile().

- sre: Added experimental expand() method to match objects.  Does not
  use buffer interface on Unicode strings.  Does not hang if group id
  is followed by whitespace.

- StringIO: Size hint in readlines() is now supported as documented.

- struct: Check ranges for bytes and shorts.

- urllib: Improved handling of win32 proxy settings. Fixed quote and
  quote_plus functions so that the always encode a comma.

- Tkinter: Image objects are now guaranteed to have unique ids.  Set
  event.delta to zero if Tk version doesn't support mousewheel.
  Removed some debugging prints.

- UserList: now implements __contains__().

- webbrowser: On Windows, use os.startfile() instead of os.popen(),
  which works around a bug in Norton AntiVirus 2000 that leads directly
  to a Blue Screen freeze.

- xml: New version detection code allows PyXML to override standard
  XML package if PyXML version is greater than 0.6.1.

- xml.dom: DOM level 1 support for basic XML.  Includes xml.dom.minidom
  (conventional DOM), and xml.dom.pulldom, which allows building the DOM
  tree only for nodes which are sufficiently interesting to a specific
  application.  Does not provide the HTML-specific extensions.  Still
  undocumented.

- xml.sax: SAX 2 support for Python, including all the handler
  interfaces needed to process XML 1.0 compliant XML.  Some
  documentation is already available.

- pyexpat: Renamed to xml.parsers.expat since this is part of the new,
  packagized XML support.


C API

- Add three new convenience functions for module initialization --
  PyModule_AddObject(), PyModule_AddIntConstant(), and
  PyModule_AddStringConstant().

- Cleaned up definition of NULL in C source code; all definitions were
  removed and add #error to Python.h if NULL isn't defined after
  #include of stdio.h.

- Py_PROTO() macros that were removed in 2.0b1 have been restored for
  backwards compatibility (at the source level) with old extensions.

- A wrapper API was added for signal() and sigaction().  Instead of
  either function, always use PyOS_getsig() to get a signal handler
  and PyOS_setsig() to set one.  A new convenience typedef
  PyOS_sighandler_t is defined for the type of signal handlers.

- Add PyString_AsStringAndSize() function that provides access to the
  internal data buffer and size of a string object -- or the default
  encoded version of a Unicode object.

- PyString_Size() and PyString_AsString() accept Unicode objects.

- The standard header <limits.h> is now included by Python.h (if it
  exists).  INT_MAX and LONG_MAX will always be defined, even if
  <limits.h> 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:

    [<expression> for <variable> in <sequence>]

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:

    [<expression> for <variable> in <sequence> if <condition>]

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/


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