Misc/NEWS - platform/external/python/cpython2 - Gitiles

 What's New in Python 2.0b1?
 ===========================

 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/)

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

 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.

 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


 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, [x**2 for i in range(4)] yields the list [0, 1, 4, 9].
 This is more efficient than map() with a lambda.

 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 filter() with a lambda.

 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.


 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.


 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 used.  Thus:

     print >> None, "Hello world"

 is equivalent to

     print "Hello world"

 Design and implementation by Barry Warsaw.


 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)].

 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)


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

 ftplib - ntransfercmd(), transfercmd(), and retrbinary() all now
 optionally support the RFC 959 REST command.

 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.

 XXX: I'm sure there are others


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

 XXX: are there any?  If not, say "None" here.


 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.

 Numerous new APIs were added, e.g.

 	XXX: Fill this out.

 ======================================================================
	What's New in Python 2.0b1?
	===========================

	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/)

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

	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.

	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


	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, [x**2 for i in range(4)] yields the list [0, 1, 4, 9].
	This is more efficient than map() with a lambda.

	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 filter() with a lambda.

	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.


	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.


	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 used. Thus:

	print >> None, "Hello world"

	is equivalent to

	print "Hello world"

	Design and implementation by Barry Warsaw.


	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)].

	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)


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

	ftplib - ntransfercmd(), transfercmd(), and retrbinary() all now
	optionally support the RFC 959 REST command.

	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.

	XXX: I'm sure there are others


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

	XXX: are there any? If not, say "None" here.


	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.

	Numerous new APIs were added, e.g.

	XXX: Fill this out.

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