| 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.) |
| |
| Vladimir Marangozov redesigned more rational APIs for allocating |
| memory. See pymem.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. |
| |
| ====================================================================== |