blob: 226f9b1af5858dbc352a0f68a018e4cab031157d [file] [log] [blame]
Guido van Rossumf2ffce02000-09-05 04:38:34 +00001What's New in Python 2.0b1?
Guido van Rossum61000331997-08-15 04:39:58 +00002===========================
3
Guido van Rossum8ed602b2000-09-01 22:34:33 +00004Below is a list of all relevant changes since release 1.6. Older
Guido van Rossumf2ffce02000-09-05 04:38:34 +00005changes are in the file HISTORY. If you are making the jump directly
6from Python 1.5.2 to 2.0, make sure to read the section for 1.6 in the
7HISTORY file! Many important changes listed there.
Guido van Rossum61000331997-08-15 04:39:58 +00008
Guido van Rossumf2ffce02000-09-05 04:38:34 +00009Alternatively, a good overview of the changes between 1.5.2 and 2.0 is
10the document "What's New in Python 2.0" by Kuchling and Moshe Zadka:
11http://starship.python.net/crew/amk/python/writing/new-python/.
Guido van Rossum1f83cce1997-10-06 21:04:35 +000012
Guido van Rossumf2ffce02000-09-05 04:38:34 +000013--Guido van Rossum (home page: http://www.pythonlabs.com/~guido/)
Guido van Rossum437cfe81999-04-08 20:17:57 +000014
15======================================================================
16
Guido van Rossumf2ffce02000-09-05 04:38:34 +000017Source Incompatibilities
18------------------------
19
20None. Note that 1.6 introduced several incompatibilities with 1.5.2,
21such as single-argument append(), connect() and bind(), and changes to
22str(long) and repr(float).
23
24
25Binary Incompatibilities
26------------------------
27
28- Third party extensions built for Python 1.5.x or 1.6 cannot be used
29with Python 2.0; these extensions will have to be rebuilt for Python
302.0.
31
32- On Windows, attempting to import a third party extension built for
33Python 1.5.x or 1.6 results in an immediate crash; there's not much we
34can do about this. Check your PYTHONPATH environment variable!
35
36- Python bytecode files (*.pyc and *.pyo) are not compatible between
37releases.
38
39
40Overview of Changes Since 1.6
41-----------------------------
42
43There are many new modules (including brand new XML support through
44the xml package, and i18n support through the gettext module); a list
45of all new modules is included below. Lots of bugs have been fixed.
46
47There are several important syntax enhancements, described in more
48detail below:
49
50 - Augmented assignment, e.g. x += 1
51
52 - List comprehensions, e.g. [x**2 for x in range(10)]
53
54 - Extended import statement, e.g. import Module as Name
55
56 - Extended print statement, e.g. print >> file, "Hello"
57
58Other important changes:
59
60 - Optional collection of cyclical garbage
61
62
63Augmented Assignment
64--------------------
65
66This must have been the most-requested feature of the past years!
67Eleven new assignment operators were added:
68
Guido van Rossume905e952000-09-05 12:42:46 +000069 += -= *= /= %= **= <<= >>= &= ^= |=
Guido van Rossumf2ffce02000-09-05 04:38:34 +000070
71For example,
72
73 A += B
74
75is similar to
76
77 A = A + B
78
79except that A is evaluated only once (relevant when A is something
80like dict[index].attr).
81
82However, if A is a mutable object, A may be modified in place. Thus,
83if A is a number or a string, A += B has the same effect as A = A+B
84(except A is only evaluated once); but if a is a list, A += B has the
85same effect as A.extend(B)!
86
87Classes and built-in object types can override the new operators in
88order to implement the in-place behavior; the not-in-place behavior is
89used automatically as a fallback when an object doesn't implement the
90in-place behavior. For classes, the method name is derived from the
91method name for the corresponding not-in-place operator by inserting
92an 'i' in front of the name, e.g. __iadd__ implements in-place
93__add__.
94
95Augmented assignment was implemented by Thomas Wouters.
96
97
98List Comprehensions
99-------------------
100
101This is a flexible new notation for lists whose elements are computed
102from another list (or lists). The simplest form is:
103
104 [<expression> for <variable> in <sequence>]
105
106For example, [x**2 for i in range(4)] yields the list [0, 1, 4, 9].
107This is more efficient than map() with a lambda.
108
109You can also add a condition:
110
111 [<expression> for <variable> in <sequence> if <condition>]
112
113For example, [w for w in words if w == w.lower()] would yield the list
114of words that contain no uppercase characters. This is more efficient
115than filter() with a lambda.
116
117You can also have nested for loops and more than one 'if' clause. For
118example, here's a function that flattens a sequence of sequences::
119
120 def flatten(seq):
121 return [x for subseq in seq for x in subseq]
122
123 flatten([[0], [1,2,3], [4,5], [6,7,8,9], []])
124
125This prints
126
127 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
128
129List comprehensions originated as a patch set from Greg Ewing; Skip
130Montanaro and Thomas Wouters also contributed.
131
132
133Extended Import Statement
134-------------------------
135
136Many people have asked for a way to import a module under a different
137name. This can be accomplished like this:
138
139 import foo
140 bar = foo
141 del foo
142
143but this common idiom gets old quickly. A simple extension of the
144import statement now allows this to be written as follows:
145
146 import foo as bar
147
148There's also a variant for 'from ... import':
149
150 from foo import bar as spam
151
152This also works with packages; e.g. you can write this:
153
154 import test.regrtest as regrtest
155
156Note that 'as' is not a new keyword -- it is recognized only in this
157context (this is only possible because the syntax for the import
158statement doesn't involve expressions).
159
160Implemented by Thomas Wouters.
161
162
163Extended Print Statement
164------------------------
165
166Easily the most controversial new feature, this extension to the print
167statement adds an option to make the output go to a different file
168than the default sys.stdout.
169
170For example, to write an error message to sys.stderr, you can now
171write:
172
173 print >> sys.stderr, "Error: bad dog!"
174
175As a special feature, if the expression used to indicate the file
176evaluates to None, the current value of sys.stdout used. Thus:
177
178 print >> None, "Hello world"
179
180is equivalent to
181
182 print "Hello world"
183
184Design and implementation by Barry Warsaw.
185
186
187Optional Collection of Cyclical Garbage
188---------------------------------------
189
190Python is now equipped with a garbage collector that can hunt down
191cyclical references between Python objects. It's no replacement for
192reference counting; in fact, it depends on the reference counts being
193correct, and decides that a set of objects belong to a cycle if all
194their reference counts can be accounted for from their references to
195each other. This devious scheme was first proposed by Eric Tiedemann,
196and brought to implementation by Neil Schemenauer.
197
198There's a module "gc" that lets you control some parameters of the
199garbage collection. There's also an option to the configure script
200that lets you enable or disable the garbage collection. In 2.0b1,
201it's on by default, so that we (hopefully) can collect decent user
202experience with this new feature. There are some questions about its
203performance. if it proves to be too much of a problem, we'll turn it
204off by default in the final 2.0 release.
205
206
207Smaller Changes
208---------------
209
210A new function zip() was added. zip(seq1, seq2, ...) is equivalent to
211map(None, seq1, seq2, ...) when the sequences have the same length;
212i.e. zip([1,2,3], [10,20,30]) returns [(1,10), (2,20), (3,30)]. When
213the lists are not all the same length, the shortest list wins:
214zip([1,2,3], [10,20]) returns [(1,10), (2,20)].
215
216sys.version_info is a tuple (major, minor, micro, level, serial).
217
218Dictionaries have an odd new method, setdefault(key, default).
219dict.setdefault(key, default) returns dict[key] if it exists; if not,
220it sets dict[key] to default and returns that value. Thus:
221
222 dict.setdefault(key, []).append(item)
223
224does the same work as this common idiom:
225
226 if not dict.has_key(key):
227 dict[key] = []
228 dict[key].append(item)
229
Jeremy Hyltonbdebd542000-09-05 18:28:54 +0000230New exceptions, TabError and IndentationError, thate are subclasses on
231SyntaxError. XXX
232
233The limits on the size of expressions and file in Python source code
234have been raised from 2**16 to 2**32. Previous versions of Python
235were limited because the maximum argument size the Python VM accepted
236was 2**16. This limited the size of object constructor expressions,
237e.g. [1,2,3] or {'a':1, 'b':2}, and the size of source files. This
238limit was raised thanks to a patch by Charles Waldman that effectively
239fixes the problem. It is now much more likely that you will be
240limited by available memory than by an arbitrary limit in Python.
241
242The interpreter's maximum recursion depth can be modified by Python
243programs using sys.getrecursionlimit and sys.setrecursionlimit. This
244limit is the maximum number of recursive calls that can be made by
245Python code. The limit exists to prevent infinite recursion from
246overflowing the C stack and causing a core dump. The default value is
2471000. The maximum safe value for a particular platform can be found
248by running Misc/find_recursionlimit.py.
Guido van Rossumf2ffce02000-09-05 04:38:34 +0000249
250New Modules and Packages
251------------------------
252
253atexit - for registering functions to be called when Python exits.
254
255imputil - Greg Stein's alternative API for writing custom import
256hooks.
257
258pyexpat - an interface to the Expat XML parser, contributed by Paul
259Prescod.
260
261xml - a new package with XML support code organized (so far) in three
262subpackages: xml.dom, xml.sax, and xml.parsers. Describing these
263would fill a volume. There's a special feature whereby a
264user-installed package named _xmlplus overrides the standard
265xmlpackage; this is intended to give the XML SIG a hook to distribute
266backwards-compatible updates to the standard xml package.
267
268webbrowser - a platform-independent API to launch a web browser.
269
270
Guido van Rossume905e952000-09-05 12:42:46 +0000271Changed Modules
272---------------
273
Jeremy Hyltonbdebd542000-09-05 18:28:54 +0000274calendar -- Many new functions that support features including control
275over which day of the week is the first day, returning strings instead
276of printing them. Also new symbolic constants for days of week,
277e.g. MONDAY, ..., SUNDAY.
278
279cgi -- FieldStorage objects have a getvalue method that works like a
280dictionary's get method and returns the value attribute of the object.
281
282ConfigParser -- The parser object has new methods has_option,
283remove_section, remove_option, set, and write. They allow the module
284to be used for writing config files as well as reading them.
285
286ftplib -- ntransfercmd(), transfercmd(), and retrbinary() all now
Guido van Rossume905e952000-09-05 12:42:46 +0000287optionally support the RFC 959 REST command.
288
Jeremy Hyltonbdebd542000-09-05 18:28:54 +0000289gzip -- readline and readlines now accept optional size arguments
Guido van Rossume905e952000-09-05 12:42:46 +0000290
Jeremy Hyltonbdebd542000-09-05 18:28:54 +0000291httplib -- New interfaces and support for HTTP/1.1 by Greg Stein. See
292the module doc strings for details.
Guido van Rossum830ca2a2000-09-05 15:34:16 +0000293
Jeremy Hyltonbdebd542000-09-05 18:28:54 +0000294os/popen2 -- popen2/popen3/popen4 support under Windows. popen2/popen3
295support under Unix.
296
297os/pty -- support for openpty and forkpty by Thomas Wouters.
298
299os.path -- fix semantics of os.path.commonprefix
300
301smtplib -- support for sending very long messages
302
303socket -- new function getfqdn()
304
305readline -- new functions to read, write and truncate history files.
306The readline section of the library reference manual contains an
307example.
308
309shutil -- new copyfileobj function
310
311SimpleHTTPServer, CGIHTTPServer -- Fix problems with buffering in the
312HTTP server.
313
314Tkinter -- flatten optimization by Fredrik Lundh
315
316urllib -- scans environment variables for proxy configuration,
317e.g. http_proxy.
318
319whichdb -- recognizes dumbdbm format
Guido van Rossume905e952000-09-05 12:42:46 +0000320
321
322Obsolete Modules
323----------------
324
325None. However note that 1.6 made a whole slew of modules obsolete:
326stdwin, soundex, cml, cmpcache, dircache, dump, find, grep, packmail,
327poly, zmod, strop, util, whatsound.
328
329
330Changed, New, Obsolete Tools
331----------------------------
332
333XXX: are there any? If not, say "None" here.
334
335
Guido van Rossumf2ffce02000-09-05 04:38:34 +0000336C-level Changes
337---------------
338
339Several cleanup jobs were carried out throughout the source code.
340
341All C code was converted to ANSI C; we got rid of all uses of the
342Py_PROTO() macro, which makes the header files a lot more readable.
343
344Most of the portability hacks were moved to a new header file,
345pyport.h; several other new header files were added and some old
346header files were removed, in an attempt to create a more rational set
347of header files. (Few of these ever need to be included explicitly;
348they are all included by Python.h.)
349
Guido van Rossumf2ffce02000-09-05 04:38:34 +0000350Trent Mick ensured portability to 64-bit platforms, under both Linux
351and Win64, especially for the new Intel Itanium processor.
352
Jeremy Hyltonbdebd542000-09-05 18:28:54 +0000353The C APIs to return an object's size have been update to consistently
354use the form PyXXX_Size, e.g. PySequence_Size and PyDict_Size. In
355previous versions, the abstract interfaces used PyXXX_Length and the
356concrete interfaces used PyXXX_Size. The old names,
357e.g. PyObject_Length, are still available for backwards compatibility
358at the API level, but are deprecated.
359
360PyOS_CheckStack - XXX
361
362The GC changes resulted in creation of two new slots on object,
363tp_traverse and tp_clear. The augmented assignment changes result in
364the createion of a new slot for each in-place operator.
365
366The GC API creates new requirements for container types implemented in
367C extesion modules. See Include/objimpl.h for details.
368
369PyString_Decode / PyString_Encode. ???
370
Guido van Rossume905e952000-09-05 12:42:46 +0000371Numerous new APIs were added, e.g.
372
373 XXX: Fill this out.
Guido van Rossumab9d6f01998-08-10 22:01:13 +0000374
375======================================================================