Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 1 | \documentclass{howto} |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 2 | % $Id$ |
| 3 | |
| 4 | \title{What's New in Python 2.3} |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 5 | \release{0.03} |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 6 | \author{A.M. Kuchling} |
| 7 | \authoraddress{\email{akuchlin@mems-exchange.org}} |
Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 8 | |
| 9 | \begin{document} |
| 10 | \maketitle |
| 11 | \tableofcontents |
| 12 | |
Andrew M. Kuchling | f70a0a8 | 2002-06-10 13:22:46 +0000 | [diff] [blame] | 13 | % Optik (or whatever it gets called) |
| 14 | % |
Andrew M. Kuchling | c61ec52 | 2002-08-04 01:20:05 +0000 | [diff] [blame] | 15 | % MacOS framework-related changes (section of its own, probably) |
| 16 | % |
Andrew M. Kuchling | 950725f | 2002-08-06 01:40:48 +0000 | [diff] [blame] | 17 | % New sorting code |
Andrew M. Kuchling | 90e9a79 | 2002-08-15 00:40:21 +0000 | [diff] [blame] | 18 | % |
Andrew M. Kuchling | 90e9a79 | 2002-08-15 00:40:21 +0000 | [diff] [blame] | 19 | % xreadlines obsolete; files are their own iterator |
Andrew M. Kuchling | f70a0a8 | 2002-06-10 13:22:46 +0000 | [diff] [blame] | 20 | |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 21 | %\section{Introduction \label{intro}} |
| 22 | |
| 23 | {\large This article is a draft, and is currently up to date for some |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 24 | random version of the CVS tree around mid-July 2002. Please send any |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 25 | additions, comments or errata to the author.} |
| 26 | |
| 27 | This article explains the new features in Python 2.3. The tentative |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 28 | release date of Python 2.3 is currently scheduled for some undefined |
| 29 | time before the end of 2002. |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 30 | |
| 31 | This article doesn't attempt to provide a complete specification of |
| 32 | the new features, but instead provides a convenient overview. For |
| 33 | full details, you should refer to the documentation for Python 2.3, |
| 34 | such as the |
| 35 | \citetitle[http://www.python.org/doc/2.3/lib/lib.html]{Python Library |
| 36 | Reference} and the |
| 37 | \citetitle[http://www.python.org/doc/2.3/ref/ref.html]{Python |
| 38 | Reference Manual}. If you want to understand the complete |
| 39 | implementation and design rationale for a change, refer to the PEP for |
| 40 | a particular new feature. |
Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 41 | |
| 42 | |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 43 | %====================================================================== |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 44 | \section{PEP 255: Simple Generators\label{section-generators}} |
Andrew M. Kuchling | f4dd65d | 2002-04-01 19:28:09 +0000 | [diff] [blame] | 45 | |
| 46 | In Python 2.2, generators were added as an optional feature, to be |
| 47 | enabled by a \code{from __future__ import generators} directive. In |
| 48 | 2.3 generators no longer need to be specially enabled, and are now |
| 49 | always present; this means that \keyword{yield} is now always a |
| 50 | keyword. The rest of this section is a copy of the description of |
| 51 | generators from the ``What's New in Python 2.2'' document; if you read |
| 52 | it when 2.2 came out, you can skip the rest of this section. |
| 53 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 54 | You're doubtless familiar with how function calls work in Python or C. |
| 55 | When you call a function, it gets a private namespace where its local |
Andrew M. Kuchling | f4dd65d | 2002-04-01 19:28:09 +0000 | [diff] [blame] | 56 | variables are created. When the function reaches a \keyword{return} |
| 57 | statement, the local variables are destroyed and the resulting value |
| 58 | is returned to the caller. A later call to the same function will get |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 59 | a fresh new set of local variables. But, what if the local variables |
Andrew M. Kuchling | f4dd65d | 2002-04-01 19:28:09 +0000 | [diff] [blame] | 60 | weren't thrown away on exiting a function? What if you could later |
| 61 | resume the function where it left off? This is what generators |
| 62 | provide; they can be thought of as resumable functions. |
| 63 | |
| 64 | Here's the simplest example of a generator function: |
| 65 | |
| 66 | \begin{verbatim} |
| 67 | def generate_ints(N): |
| 68 | for i in range(N): |
| 69 | yield i |
| 70 | \end{verbatim} |
| 71 | |
| 72 | A new keyword, \keyword{yield}, was introduced for generators. Any |
| 73 | function containing a \keyword{yield} statement is a generator |
| 74 | function; this is detected by Python's bytecode compiler which |
| 75 | compiles the function specially as a result. |
| 76 | |
| 77 | When you call a generator function, it doesn't return a single value; |
| 78 | instead it returns a generator object that supports the iterator |
| 79 | protocol. On executing the \keyword{yield} statement, the generator |
| 80 | outputs the value of \code{i}, similar to a \keyword{return} |
| 81 | statement. The big difference between \keyword{yield} and a |
| 82 | \keyword{return} statement is that on reaching a \keyword{yield} the |
| 83 | generator's state of execution is suspended and local variables are |
| 84 | preserved. On the next call to the generator's \code{.next()} method, |
| 85 | the function will resume executing immediately after the |
| 86 | \keyword{yield} statement. (For complicated reasons, the |
| 87 | \keyword{yield} statement isn't allowed inside the \keyword{try} block |
| 88 | of a \code{try...finally} statement; read \pep{255} for a full |
| 89 | explanation of the interaction between \keyword{yield} and |
| 90 | exceptions.) |
| 91 | |
| 92 | Here's a sample usage of the \function{generate_ints} generator: |
| 93 | |
| 94 | \begin{verbatim} |
| 95 | >>> gen = generate_ints(3) |
| 96 | >>> gen |
| 97 | <generator object at 0x8117f90> |
| 98 | >>> gen.next() |
| 99 | 0 |
| 100 | >>> gen.next() |
| 101 | 1 |
| 102 | >>> gen.next() |
| 103 | 2 |
| 104 | >>> gen.next() |
| 105 | Traceback (most recent call last): |
Andrew M. Kuchling | 9f6e104 | 2002-06-17 13:40:04 +0000 | [diff] [blame] | 106 | File "stdin", line 1, in ? |
| 107 | File "stdin", line 2, in generate_ints |
Andrew M. Kuchling | f4dd65d | 2002-04-01 19:28:09 +0000 | [diff] [blame] | 108 | StopIteration |
| 109 | \end{verbatim} |
| 110 | |
| 111 | You could equally write \code{for i in generate_ints(5)}, or |
| 112 | \code{a,b,c = generate_ints(3)}. |
| 113 | |
| 114 | Inside a generator function, the \keyword{return} statement can only |
| 115 | be used without a value, and signals the end of the procession of |
| 116 | values; afterwards the generator cannot return any further values. |
| 117 | \keyword{return} with a value, such as \code{return 5}, is a syntax |
| 118 | error inside a generator function. The end of the generator's results |
| 119 | can also be indicated by raising \exception{StopIteration} manually, |
| 120 | or by just letting the flow of execution fall off the bottom of the |
| 121 | function. |
| 122 | |
| 123 | You could achieve the effect of generators manually by writing your |
| 124 | own class and storing all the local variables of the generator as |
| 125 | instance variables. For example, returning a list of integers could |
| 126 | be done by setting \code{self.count} to 0, and having the |
| 127 | \method{next()} method increment \code{self.count} and return it. |
| 128 | However, for a moderately complicated generator, writing a |
| 129 | corresponding class would be much messier. |
| 130 | \file{Lib/test/test_generators.py} contains a number of more |
| 131 | interesting examples. The simplest one implements an in-order |
| 132 | traversal of a tree using generators recursively. |
| 133 | |
| 134 | \begin{verbatim} |
| 135 | # A recursive generator that generates Tree leaves in in-order. |
| 136 | def inorder(t): |
| 137 | if t: |
| 138 | for x in inorder(t.left): |
| 139 | yield x |
| 140 | yield t.label |
| 141 | for x in inorder(t.right): |
| 142 | yield x |
| 143 | \end{verbatim} |
| 144 | |
| 145 | Two other examples in \file{Lib/test/test_generators.py} produce |
| 146 | solutions for the N-Queens problem (placing $N$ queens on an $NxN$ |
| 147 | chess board so that no queen threatens another) and the Knight's Tour |
| 148 | (a route that takes a knight to every square of an $NxN$ chessboard |
| 149 | without visiting any square twice). |
| 150 | |
| 151 | The idea of generators comes from other programming languages, |
| 152 | especially Icon (\url{http://www.cs.arizona.edu/icon/}), where the |
| 153 | idea of generators is central. In Icon, every |
| 154 | expression and function call behaves like a generator. One example |
| 155 | from ``An Overview of the Icon Programming Language'' at |
| 156 | \url{http://www.cs.arizona.edu/icon/docs/ipd266.htm} gives an idea of |
| 157 | what this looks like: |
| 158 | |
| 159 | \begin{verbatim} |
| 160 | sentence := "Store it in the neighboring harbor" |
| 161 | if (i := find("or", sentence)) > 5 then write(i) |
| 162 | \end{verbatim} |
| 163 | |
| 164 | In Icon the \function{find()} function returns the indexes at which the |
| 165 | substring ``or'' is found: 3, 23, 33. In the \keyword{if} statement, |
| 166 | \code{i} is first assigned a value of 3, but 3 is less than 5, so the |
| 167 | comparison fails, and Icon retries it with the second value of 23. 23 |
| 168 | is greater than 5, so the comparison now succeeds, and the code prints |
| 169 | the value 23 to the screen. |
| 170 | |
| 171 | Python doesn't go nearly as far as Icon in adopting generators as a |
| 172 | central concept. Generators are considered a new part of the core |
| 173 | Python language, but learning or using them isn't compulsory; if they |
| 174 | don't solve any problems that you have, feel free to ignore them. |
| 175 | One novel feature of Python's interface as compared to |
| 176 | Icon's is that a generator's state is represented as a concrete object |
| 177 | (the iterator) that can be passed around to other functions or stored |
| 178 | in a data structure. |
| 179 | |
| 180 | \begin{seealso} |
| 181 | |
| 182 | \seepep{255}{Simple Generators}{Written by Neil Schemenauer, Tim |
| 183 | Peters, Magnus Lie Hetland. Implemented mostly by Neil Schemenauer |
| 184 | and Tim Peters, with other fixes from the Python Labs crew.} |
| 185 | |
| 186 | \end{seealso} |
| 187 | |
| 188 | |
| 189 | %====================================================================== |
Andrew M. Kuchling | 950725f | 2002-08-06 01:40:48 +0000 | [diff] [blame] | 190 | \section{PEP 263: \label{section-encodings}} |
| 191 | |
| 192 | Python source files can now be declared as being in different |
| 193 | character set encodings. Encodings are declared by including a |
| 194 | specially formatted comment in the first or second line of the source |
| 195 | file. For example, a UTF-8 file can be declared with: |
| 196 | |
| 197 | \begin{verbatim} |
| 198 | #!/usr/bin/env python |
| 199 | # -*- coding: UTF-8 -*- |
| 200 | \end{verbatim} |
| 201 | |
| 202 | Without such an encoding declaration, the default encoding used is |
| 203 | ISO-8859-1, also known as Latin1. |
| 204 | |
| 205 | The encoding declaration only affects Unicode string literals; the |
| 206 | text in the source code will be converted to Unicode using the |
| 207 | specified encoding. Note that Python identifiers are still restricted |
| 208 | to ASCII characters, so you can't have variable names that use |
| 209 | characters outside of the usual alphanumerics. |
| 210 | |
| 211 | \begin{seealso} |
| 212 | |
| 213 | \seepep{263}{Defining Python Source Code Encodings}{Written by |
| 214 | Marc-Andr\'e Lemburg and Martin von L\"owis; implemented by Martin von |
| 215 | L\"owis.} |
| 216 | |
| 217 | \end{seealso} |
| 218 | |
| 219 | |
| 220 | %====================================================================== |
Andrew M. Kuchling | f367651 | 2002-04-15 02:27:55 +0000 | [diff] [blame] | 221 | \section{PEP 278: Universal Newline Support} |
| 222 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 223 | The three major operating systems used today are Microsoft Windows, |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 224 | Apple's Macintosh OS, and the various \UNIX\ derivatives. A minor |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 225 | irritation is that these three platforms all use different characters |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 226 | to mark the ends of lines in text files. \UNIX\ uses character 10, |
| 227 | the ASCII linefeed, while MacOS uses character 13, the ASCII carriage |
| 228 | return, and Windows uses a two-character sequence of a carriage return |
| 229 | plus a newline. |
Andrew M. Kuchling | f367651 | 2002-04-15 02:27:55 +0000 | [diff] [blame] | 230 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 231 | Python's file objects can now support end of line conventions other |
| 232 | than the one followed by the platform on which Python is running. |
| 233 | Opening a file with the mode \samp{U} or \samp{rU} will open a file |
| 234 | for reading in universal newline mode. All three line ending |
| 235 | conventions will be translated to a \samp{\e n} in the strings |
| 236 | returned by the various file methods such as \method{read()} and |
| 237 | \method{readline()}. |
Andrew M. Kuchling | f367651 | 2002-04-15 02:27:55 +0000 | [diff] [blame] | 238 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 239 | Universal newline support is also used when importing modules and when |
| 240 | executing a file with the \function{execfile()} function. This means |
| 241 | that Python modules can be shared between all three operating systems |
| 242 | without needing to convert the line-endings. |
| 243 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 244 | This feature can be disabled at compile-time by specifying |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 245 | \longprogramopt{without-universal-newlines} when running Python's |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 246 | \file{configure} script. |
Andrew M. Kuchling | f367651 | 2002-04-15 02:27:55 +0000 | [diff] [blame] | 247 | |
| 248 | \begin{seealso} |
| 249 | |
| 250 | \seepep{278}{Universal Newline Support}{Written |
| 251 | and implemented by Jack Jansen.} |
| 252 | |
| 253 | \end{seealso} |
| 254 | |
Andrew M. Kuchling | fad2f59 | 2002-05-10 21:00:05 +0000 | [diff] [blame] | 255 | |
| 256 | %====================================================================== |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 257 | \section{PEP 279: The \function{enumerate()} Built-in Function\label{section-enumerate}} |
Andrew M. Kuchling | fad2f59 | 2002-05-10 21:00:05 +0000 | [diff] [blame] | 258 | |
| 259 | A new built-in function, \function{enumerate()}, will make |
| 260 | certain loops a bit clearer. \code{enumerate(thing)}, where |
| 261 | \var{thing} is either an iterator or a sequence, returns a iterator |
| 262 | that will return \code{(0, \var{thing[0]})}, \code{(1, |
| 263 | \var{thing[1]})}, \code{(2, \var{thing[2]})}, and so forth. Fairly |
| 264 | often you'll see code to change every element of a list that looks |
| 265 | like this: |
| 266 | |
| 267 | \begin{verbatim} |
| 268 | for i in range(len(L)): |
| 269 | item = L[i] |
| 270 | # ... compute some result based on item ... |
| 271 | L[i] = result |
| 272 | \end{verbatim} |
| 273 | |
| 274 | This can be rewritten using \function{enumerate()} as: |
| 275 | |
| 276 | \begin{verbatim} |
| 277 | for i, item in enumerate(L): |
| 278 | # ... compute some result based on item ... |
| 279 | L[i] = result |
| 280 | \end{verbatim} |
| 281 | |
| 282 | |
| 283 | \begin{seealso} |
| 284 | |
| 285 | \seepep{279}{The enumerate() built-in function}{Written |
| 286 | by Raymond D. Hettinger.} |
| 287 | |
| 288 | \end{seealso} |
| 289 | |
| 290 | |
Andrew M. Kuchling | f367651 | 2002-04-15 02:27:55 +0000 | [diff] [blame] | 291 | %====================================================================== |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 292 | \section{PEP 285: The \class{bool} Type\label{section-bool}} |
| 293 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 294 | A Boolean type was added to Python 2.3. Two new constants were added |
| 295 | to the \module{__builtin__} module, \constant{True} and |
| 296 | \constant{False}. The type object for this new type is named |
| 297 | \class{bool}; the constructor for it takes any Python value and |
| 298 | converts it to \constant{True} or \constant{False}. |
| 299 | |
| 300 | \begin{verbatim} |
| 301 | >>> bool(1) |
| 302 | True |
| 303 | >>> bool(0) |
| 304 | False |
| 305 | >>> bool([]) |
| 306 | False |
| 307 | >>> bool( (1,) ) |
| 308 | True |
| 309 | \end{verbatim} |
| 310 | |
| 311 | Most of the standard library modules and built-in functions have been |
| 312 | changed to return Booleans. |
| 313 | |
| 314 | \begin{verbatim} |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 315 | >>> obj = [] |
| 316 | >>> hasattr(obj, 'append') |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 317 | True |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 318 | >>> isinstance(obj, list) |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 319 | True |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 320 | >>> isinstance(obj, tuple) |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 321 | False |
| 322 | \end{verbatim} |
| 323 | |
| 324 | Python's Booleans were added with the primary goal of making code |
| 325 | clearer. For example, if you're reading a function and encounter the |
| 326 | statement \code{return 1}, you might wonder whether the \samp{1} |
| 327 | represents a truth value, or whether it's an index, or whether it's a |
| 328 | coefficient that multiplies some other quantity. If the statement is |
| 329 | \code{return True}, however, the meaning of the return value is quite |
| 330 | clearly a truth value. |
| 331 | |
| 332 | Python's Booleans were not added for the sake of strict type-checking. |
Andrew M. Kuchling | a2a206b | 2002-05-24 21:08:58 +0000 | [diff] [blame] | 333 | A very strict language such as Pascal would also prevent you |
| 334 | performing arithmetic with Booleans, and would require that the |
| 335 | expression in an \keyword{if} statement always evaluate to a Boolean. |
| 336 | Python is not this strict, and it never will be. (\pep{285} |
| 337 | explicitly says so.) So you can still use any expression in an |
| 338 | \keyword{if}, even ones that evaluate to a list or tuple or some |
| 339 | random object, and the Boolean type is a subclass of the |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 340 | \class{int} class, so arithmetic using a Boolean still works. |
| 341 | |
| 342 | \begin{verbatim} |
| 343 | >>> True + 1 |
| 344 | 2 |
| 345 | >>> False + 1 |
| 346 | 1 |
| 347 | >>> False * 75 |
| 348 | 0 |
| 349 | >>> True * 75 |
| 350 | 75 |
| 351 | \end{verbatim} |
| 352 | |
| 353 | To sum up \constant{True} and \constant{False} in a sentence: they're |
| 354 | alternative ways to spell the integer values 1 and 0, with the single |
| 355 | difference that \function{str()} and \function{repr()} return the |
| 356 | strings \samp{True} and \samp{False} instead of \samp{1} and \samp{0}. |
Andrew M. Kuchling | 3a52ff6 | 2002-04-03 22:44:47 +0000 | [diff] [blame] | 357 | |
| 358 | \begin{seealso} |
| 359 | |
| 360 | \seepep{285}{Adding a bool type}{Written and implemented by GvR.} |
| 361 | |
| 362 | \end{seealso} |
| 363 | |
Michael W. Hudson | 5efaf7e | 2002-06-11 10:55:12 +0000 | [diff] [blame] | 364 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 365 | \section{Extended Slices\label{section-slices}} |
Michael W. Hudson | 5efaf7e | 2002-06-11 10:55:12 +0000 | [diff] [blame] | 366 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 367 | Ever since Python 1.4, the slicing syntax has supported an optional |
| 368 | third ``step'' or ``stride'' argument. For example, these are all |
| 369 | legal Python syntax: \code{L[1:10:2]}, \code{L[:-1:1]}, |
| 370 | \code{L[::-1]}. This was added to Python included at the request of |
| 371 | the developers of Numerical Python. However, the built-in sequence |
| 372 | types of lists, tuples, and strings have never supported this feature, |
| 373 | and you got a \exception{TypeError} if you tried it. Michael Hudson |
| 374 | contributed a patch that was applied to Python 2.3 and fixed this |
| 375 | shortcoming. |
| 376 | |
| 377 | For example, you can now easily extract the elements of a list that |
| 378 | have even indexes: |
Fred Drake | df872a2 | 2002-07-03 12:02:01 +0000 | [diff] [blame] | 379 | |
| 380 | \begin{verbatim} |
| 381 | >>> L = range(10) |
| 382 | >>> L[::2] |
| 383 | [0, 2, 4, 6, 8] |
| 384 | \end{verbatim} |
| 385 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 386 | Negative values also work, so you can make a copy of the same list in |
| 387 | reverse order: |
Fred Drake | df872a2 | 2002-07-03 12:02:01 +0000 | [diff] [blame] | 388 | |
| 389 | \begin{verbatim} |
| 390 | >>> L[::-1] |
| 391 | [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] |
| 392 | \end{verbatim} |
Andrew M. Kuchling | 3a52ff6 | 2002-04-03 22:44:47 +0000 | [diff] [blame] | 393 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 394 | This also works for strings: |
| 395 | |
| 396 | \begin{verbatim} |
| 397 | >>> s='abcd' |
| 398 | >>> s[::2] |
| 399 | 'ac' |
| 400 | >>> s[::-1] |
| 401 | 'dcba' |
| 402 | \end{verbatim} |
| 403 | |
Michael W. Hudson | 4da01ed | 2002-07-19 15:48:56 +0000 | [diff] [blame] | 404 | as well as tuples and arrays. |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 405 | |
Michael W. Hudson | 4da01ed | 2002-07-19 15:48:56 +0000 | [diff] [blame] | 406 | If you have a mutable sequence (i.e. a list or an array) you can |
| 407 | assign to or delete an extended slice, but there are some differences |
| 408 | in assignment to extended and regular slices. Assignment to a regular |
| 409 | slice can be used to change the length of the sequence: |
| 410 | |
| 411 | \begin{verbatim} |
| 412 | >>> a = range(3) |
| 413 | >>> a |
| 414 | [0, 1, 2] |
| 415 | >>> a[1:3] = [4, 5, 6] |
| 416 | >>> a |
| 417 | [0, 4, 5, 6] |
| 418 | \end{verbatim} |
| 419 | |
| 420 | but when assigning to an extended slice the list on the right hand |
| 421 | side of the statement must contain the same number of items as the |
| 422 | slice it is replacing: |
| 423 | |
| 424 | \begin{verbatim} |
| 425 | >>> a = range(4) |
| 426 | >>> a |
| 427 | [0, 1, 2, 3] |
| 428 | >>> a[::2] |
| 429 | [0, 2] |
| 430 | >>> a[::2] = range(0, -2, -1) |
| 431 | >>> a |
| 432 | [0, 1, -1, 3] |
| 433 | >>> a[::2] = range(3) |
| 434 | Traceback (most recent call last): |
| 435 | File "<stdin>", line 1, in ? |
| 436 | ValueError: attempt to assign list of size 3 to extended slice of size 2 |
| 437 | \end{verbatim} |
| 438 | |
| 439 | Deletion is more straightforward: |
| 440 | |
| 441 | \begin{verbatim} |
| 442 | >>> a = range(4) |
| 443 | >>> a[::2] |
| 444 | [0, 2] |
| 445 | >>> del a[::2] |
| 446 | >>> a |
| 447 | [1, 3] |
| 448 | \end{verbatim} |
| 449 | |
| 450 | One can also now pass slice objects to builtin sequences |
| 451 | \method{__getitem__} methods: |
| 452 | |
| 453 | \begin{verbatim} |
| 454 | >>> range(10).__getitem__(slice(0, 5, 2)) |
| 455 | [0, 2, 4] |
| 456 | \end{verbatim} |
| 457 | |
| 458 | or use them directly in subscripts: |
| 459 | |
| 460 | \begin{verbatim} |
| 461 | >>> range(10)[slice(0, 5, 2)] |
| 462 | [0, 2, 4] |
| 463 | \end{verbatim} |
| 464 | |
| 465 | To make implementing sequences that support extended slicing in Python |
| 466 | easier, slice ojects now have a method \method{indices} which given |
| 467 | the length of a sequence returns \code{(start, stop, step)} handling |
| 468 | omitted and out-of-bounds indices in a manner consistent with regular |
| 469 | slices (and this innocuous phrase hides a welter of confusing |
| 470 | details!). The method is intended to be used like this: |
| 471 | |
| 472 | \begin{verbatim} |
| 473 | class FakeSeq: |
| 474 | ... |
| 475 | def calc_item(self, i): |
| 476 | ... |
| 477 | def __getitem__(self, item): |
| 478 | if isinstance(item, slice): |
| 479 | return FakeSeq([self.calc_item(i) |
| 480 | in range(*item.indices(len(self)))]) |
| 481 | else: |
| 482 | return self.calc_item(i) |
| 483 | \end{verbatim} |
| 484 | |
Andrew M. Kuchling | 90e9a79 | 2002-08-15 00:40:21 +0000 | [diff] [blame] | 485 | From this example you can also see that the builtin ``\class{slice}'' |
| 486 | object is now the type object for the slice type, and is no longer a |
| 487 | function. This is consistent with Python 2.2, where \class{int}, |
| 488 | \class{str}, etc., underwent the same change. |
| 489 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 490 | |
Andrew M. Kuchling | 3a52ff6 | 2002-04-03 22:44:47 +0000 | [diff] [blame] | 491 | %====================================================================== |
Fred Drake | df872a2 | 2002-07-03 12:02:01 +0000 | [diff] [blame] | 492 | \section{Other Language Changes} |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 493 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 494 | Here are all of the changes that Python 2.3 makes to the core Python |
| 495 | language. |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 496 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 497 | \begin{itemize} |
| 498 | \item The \keyword{yield} statement is now always a keyword, as |
| 499 | described in section~\ref{section-generators} of this document. |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 500 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 501 | \item A new built-in function \function{enumerate()} |
| 502 | was added, as described in section~\ref{section-enumerate} of this |
| 503 | document. |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 504 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 505 | \item Two new constants, \constant{True} and \constant{False} were |
| 506 | added along with the built-in \class{bool} type, as described in |
| 507 | section~\ref{section-bool} of this document. |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 508 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 509 | \item Built-in types now support the extended slicing syntax, |
| 510 | as described in section~\ref{section-slices} of this document. |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 511 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 512 | \item Dictionaries have a new method, \method{pop(\var{key})}, that |
| 513 | returns the value corresponding to \var{key} and removes that |
| 514 | key/value pair from the dictionary. \method{pop()} will raise a |
| 515 | \exception{KeyError} if the requested key isn't present in the |
| 516 | dictionary: |
| 517 | |
| 518 | \begin{verbatim} |
| 519 | >>> d = {1:2} |
| 520 | >>> d |
| 521 | {1: 2} |
| 522 | >>> d.pop(4) |
| 523 | Traceback (most recent call last): |
| 524 | File ``stdin'', line 1, in ? |
| 525 | KeyError: 4 |
| 526 | >>> d.pop(1) |
| 527 | 2 |
| 528 | >>> d.pop(1) |
| 529 | Traceback (most recent call last): |
| 530 | File ``stdin'', line 1, in ? |
| 531 | KeyError: pop(): dictionary is empty |
| 532 | >>> d |
| 533 | {} |
| 534 | >>> |
| 535 | \end{verbatim} |
| 536 | |
| 537 | (Patch contributed by Raymond Hettinger.) |
| 538 | |
Andrew M. Kuchling | 6974aa9 | 2002-08-20 00:54:36 +0000 | [diff] [blame^] | 539 | \item The \keyword{assert} statement no longer checks the \code{__debug__} |
| 540 | flag, so you can no longer disable assertions by assigning to \code{__debug__}. |
| 541 | Running Python with the \programopt{-O} switch will still generate |
| 542 | code that doesn't execute any assertions. |
| 543 | |
| 544 | \item Most type objects are now callable, so you can use them |
| 545 | to create new objects such as functions, classes, and modules. (This |
| 546 | means that the \module{new} module can be deprecated in a future |
| 547 | Python version, because you can now use the type objects available |
| 548 | in the \module{types} module.) |
| 549 | % XXX should new.py use PendingDeprecationWarning? |
| 550 | For example, you can create a new module object with the following code: |
| 551 | |
| 552 | \begin{verbatim} |
| 553 | >>> import types |
| 554 | >>> m = types.ModuleType('abc','docstring') |
| 555 | >>> m |
| 556 | <module 'abc' (built-in)> |
| 557 | >>> m.__doc__ |
| 558 | 'docstring' |
| 559 | \end{verbatim} |
| 560 | |
| 561 | \item |
| 562 | A new warning, \exception{PendingDeprecationWarning} was added to |
| 563 | indicate features which are in the process of being |
| 564 | deprecated. The warning will \emph{not} be printed by default. To |
| 565 | check for use of features that will be deprecated in the future, |
| 566 | supply \programopt{-Walways::PendingDeprecationWarning::} on the |
| 567 | command line or use \function{warnings.filterwarnings()}. |
| 568 | |
| 569 | \item Using \code{None} as a variable name will now result in a |
| 570 | \exception{SyntaxWarning} warning. In a future version of Python, |
| 571 | \code{None} may finally become a keyword. |
| 572 | |
| 573 | \item One minor but far-reaching change is that the names of extension |
| 574 | types defined by the modules included with Python now contain the |
| 575 | module and a \samp{.} in front of the type name. For example, in |
| 576 | Python 2.2, if you created a socket and printed its |
| 577 | \member{__class__}, you'd get this output: |
| 578 | |
| 579 | \begin{verbatim} |
| 580 | >>> s = socket.socket() |
| 581 | >>> s.__class__ |
| 582 | <type 'socket'> |
| 583 | \end{verbatim} |
| 584 | |
| 585 | In 2.3, you get this: |
| 586 | \begin{verbatim} |
| 587 | >>> s.__class__ |
| 588 | <type '_socket.socket'> |
| 589 | \end{verbatim} |
| 590 | |
| 591 | \end{itemize} |
| 592 | |
| 593 | |
| 594 | \subsection{String Changes} |
| 595 | |
| 596 | \begin{itemize} |
| 597 | |
| 598 | \item The \code{in} operator now works differently for strings. |
| 599 | Previously, when evaluating \code{\var{X} in \var{Y}} where \var{X} |
| 600 | and \var{Y} are strings, \var{X} could only be a single character. |
| 601 | That's now changed; \var{X} can be a string of any length, and |
| 602 | \code{\var{X} in \var{Y}} will return \constant{True} if \var{X} is a |
| 603 | substring of \var{Y}. If \var{X} is the empty string, the result is |
| 604 | always \constant{True}. |
| 605 | |
| 606 | \begin{verbatim} |
| 607 | >>> 'ab' in 'abcd' |
| 608 | True |
| 609 | >>> 'ad' in 'abcd' |
| 610 | False |
| 611 | >>> '' in 'abcd' |
| 612 | True |
| 613 | \end{verbatim} |
| 614 | |
| 615 | Note that this doesn't tell you where the substring starts; the |
| 616 | \method{find()} method is still necessary to figure that out. |
| 617 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 618 | \item The \method{strip()}, \method{lstrip()}, and \method{rstrip()} |
| 619 | string methods now have an optional argument for specifying the |
| 620 | characters to strip. The default is still to remove all whitespace |
| 621 | characters: |
| 622 | |
| 623 | \begin{verbatim} |
| 624 | >>> ' abc '.strip() |
| 625 | 'abc' |
| 626 | >>> '><><abc<><><>'.strip('<>') |
| 627 | 'abc' |
| 628 | >>> '><><abc<><><>\n'.strip('<>') |
| 629 | 'abc<><><>\n' |
| 630 | >>> u'\u4000\u4001abc\u4000'.strip(u'\u4000') |
| 631 | u'\u4001abc' |
| 632 | >>> |
| 633 | \end{verbatim} |
| 634 | |
Andrew M. Kuchling | 346386f | 2002-07-12 20:24:42 +0000 | [diff] [blame] | 635 | (Contributed by Simon Brunning.) |
| 636 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 637 | \item The \method{startswith()} and \method{endswith()} |
| 638 | string methods now accept negative numbers for the start and end |
| 639 | parameters. |
| 640 | |
| 641 | \item Another new string method is \method{zfill()}, originally a |
| 642 | function in the \module{string} module. \method{zfill()} pads a |
| 643 | numeric string with zeros on the left until it's the specified width. |
| 644 | Note that the \code{\%} operator is still more flexible and powerful |
| 645 | than \method{zfill()}. |
| 646 | |
| 647 | \begin{verbatim} |
| 648 | >>> '45'.zfill(4) |
| 649 | '0045' |
| 650 | >>> '12345'.zfill(4) |
| 651 | '12345' |
| 652 | >>> 'goofy'.zfill(6) |
| 653 | '0goofy' |
| 654 | \end{verbatim} |
| 655 | |
Andrew M. Kuchling | 346386f | 2002-07-12 20:24:42 +0000 | [diff] [blame] | 656 | (Contributed by Walter D\"orwald.) |
| 657 | |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 658 | \item A new type object, \class{basestring}, has been added. |
| 659 | Both 8-bit strings and Unicode strings inherit from this type, so |
| 660 | \code{isinstance(obj, basestring)} will return \constant{True} for |
| 661 | either kind of string. It's a completely abstract type, so you |
| 662 | can't create \class{basestring} instances. |
| 663 | |
Andrew M. Kuchling | 6974aa9 | 2002-08-20 00:54:36 +0000 | [diff] [blame^] | 664 | \item Interned strings are no longer immortal. Interned will now be |
| 665 | garbage-collected in the usual way when the only reference to them is |
| 666 | from the internal dictionary of interned strings. (Implemented by |
| 667 | Oren Tirosh.) |
| 668 | |
| 669 | \end{itemize} |
| 670 | |
| 671 | |
| 672 | \subsection{Optimizations} |
| 673 | |
| 674 | \begin{itemize} |
| 675 | |
Andrew M. Kuchling | 950725f | 2002-08-06 01:40:48 +0000 | [diff] [blame] | 676 | \item The \method{sort()} method of list objects has been extensively |
| 677 | rewritten by Tim Peters, and the implementation is significantly |
| 678 | faster. |
| 679 | |
Andrew M. Kuchling | 6974aa9 | 2002-08-20 00:54:36 +0000 | [diff] [blame^] | 680 | \item Multiplication of large long integers is now much faster thanks |
| 681 | to an implementation of Karatsuba multiplication, an algorithm that |
| 682 | scales better than the O(n*n) required for the grade-school |
| 683 | multiplication algorithm. (Original patch by Christopher A. Craig, |
| 684 | and significantly reworked by Tim Peters.) |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 685 | |
Andrew M. Kuchling | 6974aa9 | 2002-08-20 00:54:36 +0000 | [diff] [blame^] | 686 | \item The \code{SET_LINENO} opcode is now gone. This may provide a |
| 687 | small speed increase, subject to your compiler's idiosyncrasies. |
| 688 | (Removed by Michael Hudson.) |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 689 | |
Andrew M. Kuchling | 6974aa9 | 2002-08-20 00:54:36 +0000 | [diff] [blame^] | 690 | \item A number of small rearrangements have been made in various |
| 691 | hotspots to improve performance, inlining a function here, removing |
| 692 | some code there. (Implemented mostly by GvR, but lots of people have |
| 693 | contributed to one change or another.) |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 694 | |
| 695 | \end{itemize} |
Neal Norwitz | d68f517 | 2002-05-29 15:54:55 +0000 | [diff] [blame] | 696 | |
Andrew M. Kuchling | 6974aa9 | 2002-08-20 00:54:36 +0000 | [diff] [blame^] | 697 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 698 | %====================================================================== |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 699 | \section{New and Improved Modules} |
| 700 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 701 | As usual, Python's standard modules had a number of enhancements and |
Andrew M. Kuchling | a982eb1 | 2002-07-22 18:57:36 +0000 | [diff] [blame] | 702 | bug fixes. Here's a partial list of the most notable changes, sorted |
| 703 | alphabetically by module name. Consult the |
| 704 | \file{Misc/NEWS} file in the source tree for a more |
| 705 | complete list of changes, or look through the CVS logs for all the |
| 706 | details. |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 707 | |
| 708 | \begin{itemize} |
| 709 | |
Andrew M. Kuchling | a982eb1 | 2002-07-22 18:57:36 +0000 | [diff] [blame] | 710 | \item The \module{array} module now supports arrays of Unicode |
| 711 | characters using the \samp{u} format character. Arrays also now |
| 712 | support using the \code{+=} assignment operator to add another array's |
| 713 | contents, and the \code{*=} assignment operator to repeat an array. |
| 714 | (Contributed by Jason Orendorff.) |
| 715 | |
| 716 | \item The Distutils \class{Extension} class now supports |
| 717 | an extra constructor argument named \samp{depends} for listing |
| 718 | additional source files that an extension depends on. This lets |
| 719 | Distutils recompile the module if any of the dependency files are |
| 720 | modified. For example, if \samp{sampmodule.c} includes the header |
| 721 | file \file{sample.h}, you would create the \class{Extension} object like |
| 722 | this: |
| 723 | |
| 724 | \begin{verbatim} |
| 725 | ext = Extension("samp", |
| 726 | sources=["sampmodule.c"], |
| 727 | depends=["sample.h"]) |
| 728 | \end{verbatim} |
| 729 | |
| 730 | Modifying \file{sample.h} would then cause the module to be recompiled. |
| 731 | (Contributed by Jeremy Hylton.) |
| 732 | |
| 733 | \item Two new binary packagers were added to the Distutils. |
| 734 | \code{bdist_pkgtool} builds \file{.pkg} files to use with Solaris |
| 735 | \program{pkgtool}, and \code{bdist_sdux} builds \program{swinstall} |
| 736 | packages for use on HP-UX. |
| 737 | An abstract binary packager class, |
| 738 | \module{distutils.command.bdist_packager}, was added; this may make it |
| 739 | easier to write binary packaging commands. (Contributed by Mark |
| 740 | Alexander.) |
| 741 | |
| 742 | \item The \module{getopt} module gained a new function, |
| 743 | \function{gnu_getopt()}, that supports the same arguments as the existing |
| 744 | \function{getopt()} function but uses GNU-style scanning mode. |
| 745 | The existing \function{getopt()} stops processing options as soon as a |
| 746 | non-option argument is encountered, but in GNU-style mode processing |
| 747 | continues, meaning that options and arguments can be mixed. For |
| 748 | example: |
| 749 | |
| 750 | \begin{verbatim} |
| 751 | >>> getopt.getopt(['-f', 'filename', 'output', '-v'], 'f:v') |
| 752 | ([('-f', 'filename')], ['output', '-v']) |
| 753 | >>> getopt.gnu_getopt(['-f', 'filename', 'output', '-v'], 'f:v') |
| 754 | ([('-f', 'filename'), ('-v', '')], ['output']) |
| 755 | \end{verbatim} |
| 756 | |
| 757 | (Contributed by Peter \AA{strand}.) |
| 758 | |
| 759 | \item The \module{grp}, \module{pwd}, and \module{resource} modules |
| 760 | now return enhanced tuples: |
| 761 | |
| 762 | \begin{verbatim} |
| 763 | >>> import grp |
| 764 | >>> g = grp.getgrnam('amk') |
| 765 | >>> g.gr_name, g.gr_gid |
| 766 | ('amk', 500) |
| 767 | \end{verbatim} |
| 768 | |
Andrew M. Kuchling | 950725f | 2002-08-06 01:40:48 +0000 | [diff] [blame] | 769 | \item The new \module{heapq} module contains an implementation of a |
| 770 | heap queue algorithm. A heap is an array-like data structure that |
| 771 | keeps items in a sorted order such that, for every index k, heap[k] <= |
| 772 | heap[2*k+1] and heap[k] <= heap[2*k+2]. This makes it quick to remove |
| 773 | the smallest item, and inserting a new item while maintaining the heap |
| 774 | property is O(lg~n). (See |
| 775 | \url{http://www.nist.gov/dads/HTML/priorityque.html} for more |
| 776 | information about the priority queue data structure.) |
| 777 | |
| 778 | The Python \module{heapq} module provides \function{heappush()} and |
| 779 | \function{heappop()} functions for adding and removing items while |
| 780 | maintaining the heap property on top of some other mutable Python |
| 781 | sequence type. For example: |
| 782 | |
| 783 | \begin{verbatim} |
| 784 | >>> import heapq |
| 785 | >>> heap = [] |
| 786 | >>> for item in [3, 7, 5, 11, 1]: |
| 787 | ... heapq.heappush(heap, item) |
| 788 | ... |
| 789 | >>> heap |
| 790 | [1, 3, 5, 11, 7] |
| 791 | >>> heapq.heappop(heap) |
| 792 | 1 |
| 793 | >>> heapq.heappop(heap) |
| 794 | 3 |
| 795 | >>> heap |
| 796 | [5, 7, 11] |
| 797 | >>> |
| 798 | >>> heapq.heappush(heap, 5) |
| 799 | >>> heap = [] |
| 800 | >>> for item in [3, 7, 5, 11, 1]: |
| 801 | ... heapq.heappush(heap, item) |
| 802 | ... |
| 803 | >>> heap |
| 804 | [1, 3, 5, 11, 7] |
| 805 | >>> heapq.heappop(heap) |
| 806 | 1 |
| 807 | >>> heapq.heappop(heap) |
| 808 | 3 |
| 809 | >>> heap |
| 810 | [5, 7, 11] |
| 811 | >>> |
| 812 | \end{verbatim} |
| 813 | |
| 814 | (Contributed by Kevin O'Connor.) |
Andrew M. Kuchling | a982eb1 | 2002-07-22 18:57:36 +0000 | [diff] [blame] | 815 | |
| 816 | \item Two new functions in the \module{math} module, |
| 817 | \function{degrees(\var{rads})} and \function{radians(\var{degs})}, |
| 818 | convert between radians and degrees. Other functions in the |
| 819 | \module{math} module such as |
| 820 | \function{math.sin()} and \function{math.cos()} have always required |
| 821 | input values measured in radians. (Contributed by Raymond Hettinger.) |
| 822 | |
Andrew M. Kuchling | 52f1b76 | 2002-07-28 20:29:03 +0000 | [diff] [blame] | 823 | \item Four new functions, \function{getpgid()}, \function{killpg()}, \function{lchown()}, and \function{mknod()}, were added to the \module{posix} module that |
Andrew M. Kuchling | a982eb1 | 2002-07-22 18:57:36 +0000 | [diff] [blame] | 824 | underlies the \module{os} module. (Contributed by Gustavo Niemeyer |
| 825 | and Geert Jansen.) |
| 826 | |
| 827 | \item The parser objects provided by the \module{pyexpat} module |
| 828 | can now optionally buffer character data, resulting in fewer calls to |
| 829 | your character data handler and therefore faster performance. Setting |
| 830 | the parser object's \member{buffer_text} attribute to \constant{True} |
| 831 | will enable buffering. |
| 832 | |
| 833 | \item The \module{readline} module also gained a number of new |
| 834 | functions: \function{get_history_item()}, |
| 835 | \function{get_current_history_length()}, and \function{redisplay()}. |
| 836 | |
| 837 | \item Support for more advanced POSIX signal handling was added |
| 838 | to the \module{signal} module by adding the \function{sigpending}, |
| 839 | \function{sigprocmask} and \function{sigsuspend} functions, where supported |
| 840 | by the platform. These functions make it possible to avoid some previously |
| 841 | unavoidable race conditions. |
| 842 | |
| 843 | \item The \module{socket} module now supports timeouts. You |
| 844 | can call the \method{settimeout(\var{t})} method on a socket object to |
| 845 | set a timeout of \var{t} seconds. Subsequent socket operations that |
| 846 | take longer than \var{t} seconds to complete will abort and raise a |
| 847 | \exception{socket.error} exception. |
| 848 | |
| 849 | The original timeout implementation was by Tim O'Malley. Michael |
| 850 | Gilfix integrated it into the Python \module{socket} module, after the |
| 851 | patch had undergone a lengthy review. After it was checked in, Guido |
| 852 | van~Rossum rewrote parts of it. This is a good example of the free |
| 853 | software development process in action. |
| 854 | |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 855 | \item The new \module{textwrap} module contains functions for wrapping |
Andrew M. Kuchling | d003a2a | 2002-06-26 13:23:55 +0000 | [diff] [blame] | 856 | strings containing paragraphs of text. The \function{wrap(\var{text}, |
| 857 | \var{width})} function takes a string and returns a list containing |
| 858 | the text split into lines of no more than the chosen width. The |
| 859 | \function{fill(\var{text}, \var{width})} function returns a single |
| 860 | string, reformatted to fit into lines no longer than the chosen width. |
| 861 | (As you can guess, \function{fill()} is built on top of |
| 862 | \function{wrap()}. For example: |
| 863 | |
| 864 | \begin{verbatim} |
| 865 | >>> import textwrap |
| 866 | >>> paragraph = "Not a whit, we defy augury: ... more text ..." |
| 867 | >>> textwrap.wrap(paragraph, 60) |
| 868 | ["Not a whit, we defy augury: there's a special providence in", |
| 869 | "the fall of a sparrow. If it be now, 'tis not to come; if it", |
| 870 | ...] |
| 871 | >>> print textwrap.fill(paragraph, 35) |
| 872 | Not a whit, we defy augury: there's |
| 873 | a special providence in the fall of |
| 874 | a sparrow. If it be now, 'tis not |
| 875 | to come; if it be not to come, it |
| 876 | will be now; if it be not now, yet |
| 877 | it will come: the readiness is all. |
| 878 | >>> |
| 879 | \end{verbatim} |
| 880 | |
| 881 | The module also contains a \class{TextWrapper} class that actually |
| 882 | implements the text wrapping strategy. Both the |
| 883 | \class{TextWrapper} class and the \function{wrap()} and |
| 884 | \function{fill()} functions support a number of additional keyword |
| 885 | arguments for fine-tuning the formatting; consult the module's |
| 886 | documentation for details. |
| 887 | % XXX add a link to the module docs? |
| 888 | (Contributed by Greg Ward.) |
| 889 | |
Andrew M. Kuchling | ef5d06b | 2002-07-22 19:21:06 +0000 | [diff] [blame] | 890 | \item The \module{time} module's \function{strptime()} function has |
| 891 | long been an annoyance because it uses the platform C library's |
| 892 | \function{strptime()} implementation, and different platforms |
| 893 | sometimes have odd bugs. Brett Cannon contributed a portable |
| 894 | implementation that's written in pure Python, which should behave |
| 895 | identically on all platforms. |
| 896 | |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 897 | \item The DOM implementation |
| 898 | in \module{xml.dom.minidom} can now generate XML output in a |
| 899 | particular encoding, by specifying an optional encoding argument to |
| 900 | the \method{toxml()} and \method{toprettyxml()} methods of DOM nodes. |
| 901 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 902 | \end{itemize} |
| 903 | |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 904 | |
Andrew M. Kuchling | ef5d06b | 2002-07-22 19:21:06 +0000 | [diff] [blame] | 905 | %====================================================================== |
| 906 | \section{Specialized Object Allocator (pymalloc)\label{section-pymalloc}} |
| 907 | |
| 908 | An experimental feature added to Python 2.1 was a specialized object |
| 909 | allocator called pymalloc, written by Vladimir Marangozov. Pymalloc |
| 910 | was intended to be faster than the system \cfunction{malloc()} and have |
| 911 | less memory overhead for typical allocation patterns of Python |
| 912 | programs. The allocator uses C's \cfunction{malloc()} function to get |
| 913 | large pools of memory, and then fulfills smaller memory requests from |
| 914 | these pools. |
| 915 | |
| 916 | In 2.1 and 2.2, pymalloc was an experimental feature and wasn't |
| 917 | enabled by default; you had to explicitly turn it on by providing the |
| 918 | \longprogramopt{with-pymalloc} option to the \program{configure} |
| 919 | script. In 2.3, pymalloc has had further enhancements and is now |
| 920 | enabled by default; you'll have to supply |
| 921 | \longprogramopt{without-pymalloc} to disable it. |
| 922 | |
| 923 | This change is transparent to code written in Python; however, |
| 924 | pymalloc may expose bugs in C extensions. Authors of C extension |
| 925 | modules should test their code with the object allocator enabled, |
| 926 | because some incorrect code may cause core dumps at runtime. There |
| 927 | are a bunch of memory allocation functions in Python's C API that have |
| 928 | previously been just aliases for the C library's \cfunction{malloc()} |
| 929 | and \cfunction{free()}, meaning that if you accidentally called |
| 930 | mismatched functions, the error wouldn't be noticeable. When the |
| 931 | object allocator is enabled, these functions aren't aliases of |
| 932 | \cfunction{malloc()} and \cfunction{free()} any more, and calling the |
| 933 | wrong function to free memory may get you a core dump. For example, |
| 934 | if memory was allocated using \cfunction{PyObject_Malloc()}, it has to |
| 935 | be freed using \cfunction{PyObject_Free()}, not \cfunction{free()}. A |
| 936 | few modules included with Python fell afoul of this and had to be |
| 937 | fixed; doubtless there are more third-party modules that will have the |
| 938 | same problem. |
| 939 | |
| 940 | As part of this change, the confusing multiple interfaces for |
| 941 | allocating memory have been consolidated down into two API families. |
| 942 | Memory allocated with one family must not be manipulated with |
| 943 | functions from the other family. |
| 944 | |
| 945 | There is another family of functions specifically for allocating |
| 946 | Python \emph{objects} (as opposed to memory). |
| 947 | |
| 948 | \begin{itemize} |
| 949 | \item To allocate and free an undistinguished chunk of memory use |
| 950 | the ``raw memory'' family: \cfunction{PyMem_Malloc()}, |
| 951 | \cfunction{PyMem_Realloc()}, and \cfunction{PyMem_Free()}. |
| 952 | |
| 953 | \item The ``object memory'' family is the interface to the pymalloc |
| 954 | facility described above and is biased towards a large number of |
| 955 | ``small'' allocations: \cfunction{PyObject_Malloc}, |
| 956 | \cfunction{PyObject_Realloc}, and \cfunction{PyObject_Free}. |
| 957 | |
| 958 | \item To allocate and free Python objects, use the ``object'' family |
| 959 | \cfunction{PyObject_New()}, \cfunction{PyObject_NewVar()}, and |
| 960 | \cfunction{PyObject_Del()}. |
| 961 | \end{itemize} |
| 962 | |
| 963 | Thanks to lots of work by Tim Peters, pymalloc in 2.3 also provides |
| 964 | debugging features to catch memory overwrites and doubled frees in |
| 965 | both extension modules and in the interpreter itself. To enable this |
| 966 | support, turn on the Python interpreter's debugging code by running |
| 967 | \program{configure} with \longprogramopt{with-pydebug}. |
| 968 | |
| 969 | To aid extension writers, a header file \file{Misc/pymemcompat.h} is |
| 970 | distributed with the source to Python 2.3 that allows Python |
| 971 | extensions to use the 2.3 interfaces to memory allocation and compile |
| 972 | against any version of Python since 1.5.2. You would copy the file |
| 973 | from Python's source distribution and bundle it with the source of |
| 974 | your extension. |
| 975 | |
| 976 | \begin{seealso} |
| 977 | |
| 978 | \seeurl{http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/python/python/dist/src/Objects/obmalloc.c} |
| 979 | {For the full details of the pymalloc implementation, see |
| 980 | the comments at the top of the file \file{Objects/obmalloc.c} in the |
| 981 | Python source code. The above link points to the file within the |
| 982 | SourceForge CVS browser.} |
| 983 | |
| 984 | \end{seealso} |
| 985 | |
| 986 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 987 | % ====================================================================== |
| 988 | \section{Build and C API Changes} |
| 989 | |
Andrew M. Kuchling | 3c305d9 | 2002-07-22 18:50:11 +0000 | [diff] [blame] | 990 | Changes to Python's build process and to the C API include: |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 991 | |
| 992 | \begin{itemize} |
| 993 | |
Andrew M. Kuchling | ef5d06b | 2002-07-22 19:21:06 +0000 | [diff] [blame] | 994 | \item The C-level interface to the garbage collector has been changed, |
| 995 | to make it easier to write extension types that support garbage |
| 996 | collection, and to make it easier to debug misuses of the functions. |
| 997 | Various functions have slightly different semantics, so a bunch of |
| 998 | functions had to be renamed. Extensions that use the old API will |
| 999 | still compile but will \emph{not} participate in garbage collection, |
| 1000 | so updating them for 2.3 should be considered fairly high priority. |
| 1001 | |
| 1002 | To upgrade an extension module to the new API, perform the following |
| 1003 | steps: |
| 1004 | |
| 1005 | \begin{itemize} |
| 1006 | |
| 1007 | \item Rename \cfunction{Py_TPFLAGS_GC} to \cfunction{PyTPFLAGS_HAVE_GC}. |
| 1008 | |
| 1009 | \item Use \cfunction{PyObject_GC_New} or \cfunction{PyObject_GC_NewVar} to |
| 1010 | allocate objects, and \cfunction{PyObject_GC_Del} to deallocate them. |
| 1011 | |
| 1012 | \item Rename \cfunction{PyObject_GC_Init} to \cfunction{PyObject_GC_Track} and |
| 1013 | \cfunction{PyObject_GC_Fini} to \cfunction{PyObject_GC_UnTrack}. |
| 1014 | |
| 1015 | \item Remove \cfunction{PyGC_HEAD_SIZE} from object size calculations. |
| 1016 | |
| 1017 | \item Remove calls to \cfunction{PyObject_AS_GC} and \cfunction{PyObject_FROM_GC}. |
| 1018 | |
| 1019 | \end{itemize} |
| 1020 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1021 | \item Python can now optionally be built as a shared library |
| 1022 | (\file{libpython2.3.so}) by supplying \longprogramopt{enable-shared} |
Andrew M. Kuchling | fad2f59 | 2002-05-10 21:00:05 +0000 | [diff] [blame] | 1023 | when running Python's \file{configure} script. (Contributed by Ondrej |
| 1024 | Palkovsky.) |
Andrew M. Kuchling | f4dd65d | 2002-04-01 19:28:09 +0000 | [diff] [blame] | 1025 | |
Michael W. Hudson | dd32a91 | 2002-08-15 14:59:02 +0000 | [diff] [blame] | 1026 | \item The \csimplemacro{DL_EXPORT} and \csimplemacro{DL_IMPORT} macros |
| 1027 | are now deprecated. Initialization functions for Python extension |
| 1028 | modules should now be declared using the new macro |
Andrew M. Kuchling | 3c305d9 | 2002-07-22 18:50:11 +0000 | [diff] [blame] | 1029 | \csimplemacro{PyMODINIT_FUNC}, while the Python core will generally |
| 1030 | use the \csimplemacro{PyAPI_FUNC} and \csimplemacro{PyAPI_DATA} |
| 1031 | macros. |
Neal Norwitz | bba23a8 | 2002-07-22 13:18:59 +0000 | [diff] [blame] | 1032 | |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 1033 | \item The interpreter can be compiled without any docstrings for |
| 1034 | the built-in functions and modules by supplying |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 1035 | \longprogramopt{without-doc-strings} to the \file{configure} script. |
Andrew M. Kuchling | e995d16 | 2002-07-11 20:09:50 +0000 | [diff] [blame] | 1036 | This makes the Python executable about 10\% smaller, but will also |
| 1037 | mean that you can't get help for Python's built-ins. (Contributed by |
| 1038 | Gustavo Niemeyer.) |
| 1039 | |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 1040 | \item The cycle detection implementation used by the garbage collection |
| 1041 | has proven to be stable, so it's now being made mandatory; you can no |
| 1042 | longer compile Python without it, and the |
| 1043 | \longprogramopt{with-cycle-gc} switch to \file{configure} has been removed. |
| 1044 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1045 | \item The \cfunction{PyArg_NoArgs()} macro is now deprecated, and code |
Andrew M. Kuchling | 7845e7c | 2002-07-11 19:27:46 +0000 | [diff] [blame] | 1046 | that uses it should be changed. For Python 2.2 and later, the method |
| 1047 | definition table can specify the |
| 1048 | \constant{METH_NOARGS} flag, signalling that there are no arguments, and |
| 1049 | the argument checking can then be removed. If compatibility with |
| 1050 | pre-2.2 versions of Python is important, the code could use |
| 1051 | \code{PyArg_ParseTuple(args, "")} instead, but this will be slower |
| 1052 | than using \constant{METH_NOARGS}. |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 1053 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1054 | \item A new function, \cfunction{PyObject_DelItemString(\var{mapping}, |
| 1055 | char *\var{key})} was added |
| 1056 | as shorthand for |
| 1057 | \code{PyObject_DelItem(\var{mapping}, PyString_New(\var{key})}. |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 1058 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 1059 | \item The source code for the Expat XML parser is now included with |
| 1060 | the Python source, so the \module{pyexpat} module is no longer |
| 1061 | dependent on having a system library containing Expat. |
| 1062 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1063 | \item File objects now manage their internal string buffer |
| 1064 | differently by increasing it exponentially when needed. |
| 1065 | This results in the benchmark tests in \file{Lib/test/test_bufio.py} |
| 1066 | speeding up from 57 seconds to 1.7 seconds, according to one |
| 1067 | measurement. |
| 1068 | |
Andrew M. Kuchling | 72b58e0 | 2002-05-29 17:30:34 +0000 | [diff] [blame] | 1069 | \item It's now possible to define class and static methods for a C |
| 1070 | extension type by setting either the \constant{METH_CLASS} or |
| 1071 | \constant{METH_STATIC} flags in a method's \ctype{PyMethodDef} |
| 1072 | structure. |
Andrew M. Kuchling | 45afd54 | 2002-04-02 14:25:25 +0000 | [diff] [blame] | 1073 | |
Andrew M. Kuchling | 346386f | 2002-07-12 20:24:42 +0000 | [diff] [blame] | 1074 | \item Python now includes a copy of the Expat XML parser's source code, |
| 1075 | removing any dependence on a system version or local installation of |
| 1076 | Expat. |
| 1077 | |
Andrew M. Kuchling | 821013e | 2002-05-06 17:46:39 +0000 | [diff] [blame] | 1078 | \end{itemize} |
| 1079 | |
| 1080 | \subsection{Port-Specific Changes} |
| 1081 | |
Andrew M. Kuchling | 187b1d8 | 2002-05-29 19:20:57 +0000 | [diff] [blame] | 1082 | Support for a port to IBM's OS/2 using the EMX runtime environment was |
| 1083 | merged into the main Python source tree. EMX is a POSIX emulation |
| 1084 | layer over the OS/2 system APIs. The Python port for EMX tries to |
| 1085 | support all the POSIX-like capability exposed by the EMX runtime, and |
| 1086 | mostly succeeds; \function{fork()} and \function{fcntl()} are |
| 1087 | restricted by the limitations of the underlying emulation layer. The |
| 1088 | standard OS/2 port, which uses IBM's Visual Age compiler, also gained |
| 1089 | support for case-sensitive import semantics as part of the integration |
| 1090 | of the EMX port into CVS. (Contributed by Andrew MacIntyre.) |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 1091 | |
Andrew M. Kuchling | 72b58e0 | 2002-05-29 17:30:34 +0000 | [diff] [blame] | 1092 | On MacOS, most toolbox modules have been weaklinked to improve |
| 1093 | backward compatibility. This means that modules will no longer fail |
| 1094 | to load if a single routine is missing on the curent OS version. |
Andrew M. Kuchling | 187b1d8 | 2002-05-29 19:20:57 +0000 | [diff] [blame] | 1095 | Instead calling the missing routine will raise an exception. |
| 1096 | (Contributed by Jack Jansen.) |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 1097 | |
Andrew M. Kuchling | 187b1d8 | 2002-05-29 19:20:57 +0000 | [diff] [blame] | 1098 | The RPM spec files, found in the \file{Misc/RPM/} directory in the |
| 1099 | Python source distribution, were updated for 2.3. (Contributed by |
| 1100 | Sean Reifschneider.) |
Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 1101 | |
Andrew M. Kuchling | 20e5abc | 2002-07-11 20:50:34 +0000 | [diff] [blame] | 1102 | Python now supports AtheOS (\url{www.atheos.cx}) and GNU/Hurd. |
| 1103 | |
Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 1104 | |
| 1105 | %====================================================================== |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1106 | \section{Other Changes and Fixes} |
| 1107 | |
| 1108 | Finally, there are various miscellaneous fixes: |
| 1109 | |
| 1110 | \begin{itemize} |
| 1111 | |
| 1112 | \item The tools used to build the documentation now work under Cygwin |
| 1113 | as well as \UNIX. |
| 1114 | |
Michael W. Hudson | dd32a91 | 2002-08-15 14:59:02 +0000 | [diff] [blame] | 1115 | \item The \code{SET_LINENO} opcode has been removed. Back in the |
| 1116 | mists of time, this opcode was needed to produce line numbers in |
| 1117 | tracebacks and support trace functions (for, e.g., \module{pdb}). |
| 1118 | Since Python 1.5, the line numbers in tracebacks have been computed |
| 1119 | using a different mechanism that works with ``python -O''. For Python |
| 1120 | 2.3 Michael Hudson implemented a similar scheme to determine when to |
| 1121 | call the trace function, removing the need for \code{SET_LINENO} |
| 1122 | entirely. |
| 1123 | |
| 1124 | Python code will be hard pushed to notice a difference from this |
| 1125 | change, apart from a slight speed up when python is run without |
| 1126 | \programopt{-O}. |
| 1127 | |
| 1128 | C extensions that access the \member{f_lineno} field of frame objects |
| 1129 | should instead call \code{PyCode_Addr2Line(f->f_code, f->f_lasti)}. |
| 1130 | This will have the added effect of making the code work as desired |
| 1131 | under ``python -O'' in earlier versions of Python. |
| 1132 | |
| 1133 | To make tracing work as expected, it was found necessary to add a new |
| 1134 | opcode, \cdata{RETURN_NONE}, to the VM. If you want to know why, read |
| 1135 | the comments in the function \cfunction{maybe_call_line_trace} in |
| 1136 | \file{Python/ceval.c}. |
| 1137 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1138 | \end{itemize} |
| 1139 | |
Andrew M. Kuchling | 187b1d8 | 2002-05-29 19:20:57 +0000 | [diff] [blame] | 1140 | |
Andrew M. Kuchling | 517109b | 2002-05-07 21:01:16 +0000 | [diff] [blame] | 1141 | %====================================================================== |
Andrew M. Kuchling | 950725f | 2002-08-06 01:40:48 +0000 | [diff] [blame] | 1142 | \section{Porting to Python 2.3} |
| 1143 | |
| 1144 | XXX write this |
| 1145 | |
| 1146 | |
| 1147 | %====================================================================== |
Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 1148 | \section{Acknowledgements \label{acks}} |
| 1149 | |
Andrew M. Kuchling | 03594bb | 2002-03-27 02:29:48 +0000 | [diff] [blame] | 1150 | The author would like to thank the following people for offering |
| 1151 | suggestions, corrections and assistance with various drafts of this |
Andrew M. Kuchling | 7f147a7 | 2002-06-10 18:58:19 +0000 | [diff] [blame] | 1152 | article: Michael Chermside, Scott David Daniels, Fred~L. Drake, Jr., |
Andrew M. Kuchling | 7845e7c | 2002-07-11 19:27:46 +0000 | [diff] [blame] | 1153 | Michael Hudson, Detlef Lannert, Martin von L\"owis, Andrew MacIntyre, |
Andrew M. Kuchling | 950725f | 2002-08-06 01:40:48 +0000 | [diff] [blame] | 1154 | Gustavo Niemeyer, Neal Norwitz, Jason Tishler. |
Fred Drake | 03e1031 | 2002-03-26 19:17:43 +0000 | [diff] [blame] | 1155 | |
| 1156 | \end{document} |