Mailman 3 September 2004 - Python-announce-list

ANN: PythonDoc 2.1 beta 2 (september 5, 2004)
by Fredrik Lundh Sept. 5, 2004

Sept. 5, 2004

PythonDoc is a documentation tool for Python, inspired by JavaDoc. Like JavaDoc, PythonDoc scans your Python code for doc comments, and generates API documentation in XML and HTML formats. Python- Doc supports basic JavaDoc tags like @param and @return, and adds a few Python-specific tags. You can use PythonDoc comments to describe module-level variables and constants, functions, classes, methods, and attributes. PythonDoc comes with a standard HTML generator, but you can plug in your own output handlers, or use XSTL or other tools to process the PythonDoc XML format. PythonDoc 2.1 beta 2 is a bugfix release, which handles 2.4 decorators a bit better than earlier releases. For more information on the 2.1 beta releases, see: http://article.gmane.org/gmane.comp.python.announce/4582 Downloads: http://effbot.org/downloads#pythondoc http://effbot.org/downloads#elementtree enjoy /F

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ANN: pyCallTips 0.6 released
by dm-info＠163.com Sept. 5, 2004

Sept. 5, 2004

If some pythoner complain that Vim don't support calltips of python, now I implement it. Try it and enjoy it. http://vim.sourceforge.net/scripts/script.php?script_id=1074 Intro: This script simualate code calltips in a new bottow window of Vim. In fact, it display python help doc strings of word under the cursor by scanning the imported modules in the current file. 0.6 changed: 1.enhanced 0.5 2.fixed some bugs 3.you can execute "CT_unmapkeys" to pause the script and "CT_mapkeys" to resume .

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UPDATE: New 2.4a3 Windows installer and random.py patch available
by Anthony Baxter Sept. 5, 2004

Sept. 5, 2004

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Due to a goof in the packaging scripts, the Windows installer that was released on Friday for 2.4a3 broke file associations for .py files. There's a fixed installer (python-2.4a3.2.msi) available from the Python 2.4 web page. There's also a patch for the breakage for random.py on systems that don't have support for the new os.urandom() call. This is also available from the Python 2.4 web page. ~ http://www.python.org/2.4/ We apologise to those affected by these bugs, and I'd like to thank the folks who downloaded the release and let us know about the problems so promptly. Anthony Baxter anthony(a)python.org Python Release Manager (on behalf of the entire python-dev team) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org iD8DBQFBOscVDt3F8mpFyBYRAk2xAJ9KcxQf5JOTmD6dpOiBShe/8jnWSwCgnL/S hN44eBC0mqygEhltFK2W9Ig= =W445 -----END PGP SIGNATURE-----

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Middleware'04 Call for Participation
by Middleware 04 Sept. 4, 2004

Sept. 4, 2004

ACM/IFIP/USENIX Middleware 2004 Call for Participation Renaissance Toronto Hotel at SkyDome Toronto, Ontario, Canada October 18th - 22nd, 2004 http://www.eecg.utoronto.ca/middleware2004/ Important Dates: Early Registration Rate Ends: 22 September 2004 Last Day to Pre-Register: 06 October 2004 Hotel Cut-Off Date: 25 September 2004 Hotel room reservations (Canada/US): 1-800-237-1512 Program Summary: For details and exact dates see: http://www.eecg.utoronto.ca/middleware2004/ Keynotes: How Wrong Can You Be? Getting Lost on the Road to Massive Scalability Werner Vogels, Director of Systems Research, Amazon.com Aspect-Oriented Programming - The promise and the controversy Gregor Kiczales, University of British Columbia Main conference program Single-track conference with 26 technical paper presentations and 6 work-in-progress presentations. For details see http://www.eecg.toronto.edu/middleware2004/programstruct.htm Tutorials (Monday and Tuesday): Building Distributed .NET Applications - Technologies, Architecture, Comparison with J2EE. By Michael Stal, Siemens AG Germany (Monday, full day.) Getting Started with Aspect-Oriented Programming for Middleware. By Yvonne Coady, University of Victoria, Canada (Monday, morning.) Middleware and Data Management for Sensor Networks. By Nalini Venkatasubramanian, University of California, Irvine, USA and Sharad Mehrotra,University of California, Irvine, USA (Tuesday, morning.) Enterprise Integration Patterns: Asynchronous Messaging Architectures in Practice. By Gregor Hohpe, ThoughtWorks Inc., USA (Tuesday, morning.) Data Grid Management Systems. By Arun Swaran Jagatheesan, University of California, San Diego, USA (Tuesday, afternoon.) DDS: The Real-Time Publish-Subscribe Standard for Data Distribution By Gerardo Pardo-Castellote, Real-Time Innovations Inc., USA (Tuesday, afternoon.) Workshops (Monday and Tuesday): 2nd Workshop on Middleware for Grid Computing. Organizers: Bruno Schulze - National Scientific Computing Laboratory (Brazil) and Radha Nandkumar - NCSA/UIUC (USA) (Monday, October 18th.) 2nd Workshop on Middleware for Pervasive and Ad-Hoc Computing Organizer: Paddy Nixon - Strathclyde University (UK) (Monday, October 18th.) 3rd Workshop on Adaptive and Reflective Middleware. Organizer: Fabio Costa, Federal University of Goi�s - (Brazil) and Nanbor Wang - Tech-X Corporation (USA) (Tuesday, October 19th.) 1st Middleware Doctoral Symposium. Organizers: Edward Curry - National University of Ireland (Ireland) and Doug Lea - SUNY Oswego (USA) (Tuesday, October 19th.) ---

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final version of PEP-318 "Decorators for functions and methods"
by Anthony Baxter Sept. 3, 2004

Sept. 3, 2004

To go along with the 2.4a3 release, here's an updated version of the decorator PEP. It describes the state of decorators as they are in 2.4a3. PEP: 318 Title: Decorators for Functions and Methods Version: $Revision: 1.34 $ Last-Modified: $Date: 2004/09/03 09:32:50 $ Author: Kevin D. Smith, Jim Jewett, Skip Montanaro, Anthony Baxter Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 05-Jun-2003 Python-Version: 2.4 Post-History: 09-Jun-2003, 10-Jun-2003, 27-Feb-2004, 23-Mar-2004, 30-Aug-2004, 2-Sep-2004 WarningWarningWarning ===================== This document is meant to describe the decorator syntax and the process that resulted in the decisions that were made. It does not attempt to cover the huge number of potential alternative syntaxes, nor is it an attempt to exhaustively list all the positives and negatives of each form. Abstract ======== The current method for transforming functions and methods (for instance, declaring them as a class or static method) is awkward and can lead to code that is difficult to understand. Ideally, these transformations should be made at the same point in the code where the declaration itself is made. This PEP introduces new syntax for transformations of a function or method declaration. Motivation ========== The current method of applying a transformation to a function or method places the actual transformation after the function body. For large functions this separates a key component of the function's behavior from the definition of the rest of the function's external interface. For example:: def foo(self): perform method operation foo = classmethod(foo) This becomes less readable with longer methods. It also seems less than pythonic to name the function three times for what is conceptually a single declaration. A solution to this problem is to move the transformation of the method closer to the method's own declaration. While the new syntax is not yet final, the intent is to replace:: def foo(cls): pass foo = synchronized(lock)(foo) foo = classmethod(foo) with an alternative that places the decoration in the function's declaration:: @classmethod @synchronized(lock) def foo(cls): pass Modifying classes in this fashion is also possible, though the benefits are not as immediately apparent. Almost certainly, anything which could be done with class decorators could be done using metaclasses, but using metaclasses is sufficiently obscure that there is some attraction to having an easier way to make simple modifications to classes. For Python 2.4, only function/method decorators are being added. Why Is This So Hard? -------------------- Two decorators (``classmethod()`` and ``staticmethod()``) have been available in Python since version 2.2. It's been assumed since approximately that time that some syntactic support for them would eventually be added to the language. Given this assumption, one might wonder why it's been so difficult to arrive at a consensus. Discussions have raged off-and-on at times in both comp.lang.python and the python-dev mailing list about how best to implement function decorators. There is no one clear reason why this should be so, but a few problems seem to be most divisive. * Disagreement about where the "declaration of intent" belongs. Almost everyone agrees that decorating/transforming a function at the end of its definition is suboptimal. Beyond that there seems to be no clear consensus where to place this information. * Syntactic constraints. Python is a syntactically simple language with fairly strong constraints on what can and can't be done without "messing things up" (both visually and with regards to the language parser). There's no obvious way to structure this information so that people new to the concept will think, "Oh yeah, I know what you're doing." The best that seems possible is to keep new users from creating a wildly incorrect mental model of what the syntax means. * Overall unfamiliarity with the concept. For people who have a passing acquaintance with algebra (or even basic arithmetic) or have used at least one other programming language, much of Python is intuitive. Very few people will have had any experience with the decorator concept before encountering it in Python. There's just no strong preexisting meme that captures the concept. * Syntax discussions in general appear to cause more contention than almost anything else. Readers are pointed to the ternary operator discussions that were associated with PEP 308 for another example of this. Background ========== There is general agreement that syntactic support is desirable to the current state of affairs. Guido mentioned `syntactic support for decorators`_ in his DevDay keynote presentation at the `10th Python Conference`_, though `he later said`_ it was only one of several extensions he proposed there "semi-jokingly". `Michael Hudson raised the topic`_ on ``python-dev`` shortly after the conference, attributing the initial bracketed syntax to an earlier proposal on ``comp.lang.python`` by `Gareth McCaughan`_. .. _syntactic support for decorators: http://www.python.org/doc/essays/ppt/python10/py10keynote.pdf .. _10th python conference: http://www.python.org/workshops/2002-02/ .. _michael hudson raised the topic: http://mail.python.org/pipermail/python-dev/2002-February/020005.html .. _he later said: http://mail.python.org/pipermail/python-dev/2002-February/020017.html .. _gareth mccaughan: http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=slrna40k88… Class decorations seem like an obvious next step because class definition and function definition are syntactically similar, however Guido remains unconvinced, and class decorators will almost certainly not be in Python 2.4. The discussion continued on and off on python-dev from February 2002 through July 2004. Hundreds and hundreds of posts were made, with people proposing many possible syntax variations. Guido took a list of proposals to `EuroPython 2004`_, where a discussion took place. Subsequent to this, he decided that we'd have the `Java-style`_ @decorator syntax, and this appeared for the first time in 2.4a2. Barry Warsaw named this the 'pie-decorator' syntax, in honor of the Pie-thon Parrot shootout which was occured around the same time as the decorator syntax, and because the @ looks a little like a pie. Guido `outlined his case`_ on Python-dev, including `this piece`_ on some of the (many) rejected forms. .. _EuroPython 2004: http://www.python.org/doc/essays/ppt/euro2004/euro2004.pdf .. _outlined his case: http://mail.python.org/pipermail/python-dev/2004-August/author.html .. _this piece: http://mail.python.org/pipermail/python-dev/2004-August/046672.html .. _Java-style: http://java.sun.com/j2se/1.5.0/docs/guide/language/annotations.html On the name 'Decorator' ======================= There's been a number of complaints about the choice of the name 'decorator' for this feature. The major one is that the name is not consistent with its use in the `GoF book`_. The name 'decorator' probably owes more to its use in the compiler area -- a syntax tree is walked and annotated. It's quite possible that a better name may turn up. .. _GoF book: http://patterndigest.com/patterns/Decorator.html Design Goals ============ The new syntax should * work for arbitrary wrappers, including user-defined callables and the existing builtins ``classmethod()`` and ``staticmethod()``. This requirement also means that a decorator syntax must support passing arguments to the wrapper constructor * work with multiple wrappers per definition * make it obvious what is happening; at the very least it should be obvious that new users can safely ignore it when writing their own code * be a syntax "that ... [is] easy to remember once explained" * not make future extensions more difficult * be easy to type; programs that use it are expected to use it very frequently * not make it more difficult to scan through code quickly. It should still be easy to search for all definitions, a particular definition, or the arguments that a function accepts * not needlessly complicate secondary support tools such as language-sensitive editors and other "`toy parser tools out there`_" * allow future compilers to optimize for decorators. With the hope of a JIT compiler for Python coming into existence at some point this tends to require the syntax for decorators to come before the function definition * move from the end of the function, where it's currently hidden, to the front where it is more `in your face`_ Andrew Kuchling has links to a bunch of the discussions about motivations and use cases `in his blog`_. Particularly notable is `Jim Huginin's list of use cases`_. .. _toy parser tools out there: http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&selm=mailman.10… .. _in your face: http://mail.python.org/pipermail/python-dev/2004-August/047112.html .. _in his blog: http://www.amk.ca/diary/archives/cat_python.html#003255 .. _Jim Huginin's list of use cases: http://mail.python.org/pipermail/python-dev/2004-April/044132.html Current Syntax ============== The current syntax for function decorators as implemented in Python 2.4a2 is:: @dec2 @dec1 def func(arg1, arg2, ...): pass This is equivalent to:: def func(arg1, arg2, ...): pass func = dec2(dec1(func)) without the intermediate assignment to the variable ``func``. The decorators are near the function declaration. The @ sign makes it clear that something new is going on here. The decorator statement is limited in what it can accept -- arbitrary expressions will not work. Guido preferred this because of a `gut feeling`_. .. _gut feeling: http://mail.python.org/pipermail/python-dev/2004-August/046711.html Syntax Alternatives =================== There have been `a large number`_ of different syntaxes proposed -- rather than attempting to work through these individual syntaxes, it's worthwhile to break the syntax discussion down into a number of areas. Attempting to discuss `each possible syntax`_ individually would be an act of madness, and produce a completely unwieldy PEP. .. _a large number: http://www.python.org/moin/PythonDecorators .. _each possible syntax: http://ucsu.colorado.edu/~bethard/py/decorators-output.py Decorator Location ------------------ The first syntax point is the location of the decorators. For the following examples, we use the @syntax used in 2.4a2. Decorators before the def statement are the first alternative, and the syntax used in 2.4a2:: @classmethod def foo(arg1,arg2): pass @accepts(int,int) @returns(float) def bar(low,high): pass There have been a number of objections raised to this location -- the primary one is that it's the first real Python case where a line of code has an effect on a following line. The syntax available in 2.4a3 requires one decorator per line (in a2, multiple decorators could be specified on the same line). People also complained that the syntax quickly got unwieldy when multiple decorators were used. The point was made, though, that the chances of a large number of decorators being used on a single function were small and thus this was not a large worry. Some of the advantages of this form are that the decorators live outside the method body -- they are obviously executed at the time the function is defined. Another advantage is that a prefix to the function definition fits the idea of knowing about a change to the semantics of the code before the code itself, thus you know how to interpret the code's semantics properly without having to go back and change your initial perceptions if the syntax did not come before the function definition. Guido decided `he preferred`_ having the decorators on the line before the 'def', because it was felt that a long argument list would mean that the decorators would be 'hidden' .. _he preferred: http://mail.python.org/pipermail/python-dev/2004-March/043756.html The second form is the decorators between the def and the function name, or the function name and the argument list:: def @classmethod foo(arg1,arg2): pass def @accepts(int,int),@returns(float) bar(low,high): pass def foo @classmethod (arg1,arg2): pass def bar @accepts(int,int),@returns(float) (low,high): pass There are a couple of objections to this form. The first is that it breaks easily 'greppability' of the source -- you can no longer search for 'def foo(' and find the definition of the function. The second, more serious, objection is that in the case of multiple decorators, the syntax would be extremely unwieldy. The next form, which has had a number of strong proponents, is to have the decorators between the argument list and the trailing ``:`` in the 'def' line:: def foo(arg1,arg2) @classmethod: pass def bar(low,high) @accepts(int,int),@returns(float): pass Guido `summarized the arguments`_ against this form (many of which also apply to the previous form) as: - it hides crucial information (e.g. that it is a static method) after the signature, where it is easily missed - it's easy to miss the transition between a long argument list and a long decorator list - it's cumbersome to cut and paste a decorator list for reuse, because it starts and ends in the middle of a line .. _summarized the arguments: http://mail.python.org/pipermail/python-dev/2004-August/047112.html The next form is that the decorator syntax goes inside the method body at the start, in the same place that docstrings currently live: def foo(arg1,arg2): @classmethod pass def bar(low,high): @accepts(int,int) @returns(float) pass The primary objection to this form is that it requires "peeking inside" the method body to determine the decorators. In addition, even though the code is inside the method body, it is not executed when the method is run. Guido felt that docstrings were not a good counter-example, and that it was quite possible that a 'docstring' decorator could help move the docstring to outside the function body. The final form is a new block that encloses the method's code. For this example, we'll use a 'decorate' keyword, as it makes no sense with the @syntax. :: decorate: classmethod def foo(arg1,arg2): pass decorate: accepts(int,int) returns(float) def bar(low,high): pass This form would result in inconsistent indentation for decorated and undecorated methods. In addition, a decorated method's body would start three indent levels in. Syntax forms ------------ * ``@decorator``:: @classmethod def foo(arg1,arg2): pass @accepts(int,int) @returns(float) def bar(low,high): pass The major objections against this syntax are that the @ symbol is not currently used in Python (and is used in both IPython and Leo), and that the @ symbol is not meaningful. Another objection is that this "wastes" a currently unused character (from a limited set) on something that is not perceived as a major use. * ``|decorator``:: |classmethod def foo(arg1,arg2): pass |accepts(int,int) |returns(float) def bar(low,high): pass This is a variant on the @decorator syntax -- it has the advantage that it does not break IPython and Leo. Its major disadvantage compared to the @syntax is that the | symbol looks like both a capital I and a lowercase l. * list syntax:: [classmethod] def foo(arg1,arg2): pass [accepts(int,int), returns(float)] def bar(low,high): pass The major objection to the list syntax is that it's currently meaningful (when used in the form before the method). It's also lacking any indication that the expression is a decorator. * list syntax using other brackets (``<...>``, ``[[...]]``, ...):: <classmethod> def foo(arg1,arg2): pass <accepts(int,int), returns(float)> def bar(low,high): pass None of these alternatives gained much traction. The alternatives which involve square brackets only serve to make it obvious that the decorator construct is not a list. They do nothing to make parsing any easier. The '<...>' alternative presents parsing problems because '<' and '>' already parse as un-paired. They present a further parsing ambiguity because a right angle bracket might be a greater than symbol instead of a closer for the decorators. * ``decorate()`` The ``decorate()`` proposal was that no new syntax be implemented -- instead a magic function that used introspection to manipulate the following function. Both Jp Calderone and Philip Eby produced implementations of functions that did this. Guido was pretty firmly against this -- with no new syntax, the magicness of a function like this is extremely high: Using functions with "action-at-a-distance" through sys.settraceback may be okay for an obscure feature that can't be had any other way yet doesn't merit changes to the language, but that's not the situation for decorators. The widely held view here is that decorators need to be added as a syntactic feature to avoid the problems with the postfix notation used in 2.2 and 2.3. Decorators are slated to be an important new language feature and their design needs to be forward-looking, not constrained by what can be implemented in 2.3. * _`new keyword (and block)` This idea was the consensus alternate from comp.lang.python (more on this in `Community Consensus`_ below.) Robert Brewer wrote up a detailed `J2 proposal`_ document outlining the arguments in favor of this form. The initial issues with this form are: - It requires a new keyword, and therefore a ``from __future__ import decorators`` statement. - The choice of keyword is contentious. However ``using`` emerged as the consensus choice, and is used in the proposal and implementation. - The keyword/block form produces something that looks like a normal code block, but isn't. Attempts to use statements in this block will cause a syntax error, which may confuse users. A few days later, Guido `rejected the proposal`_ on two main grounds, firstly: ... the syntactic form of an indented block strongly suggests that its contents should be a sequence of statements, but in fact it is not -- only expressions are allowed, and there is an implicit "collecting" of these expressions going on until they can be applied to the subsequent function definition. ... and secondly: ... the keyword starting the line that heads a block draws a lot of attention to it. This is true for "if", "while", "for", "try", "def" and "class". But the "using" keyword (or any other keyword in its place) doesn't deserve that attention; the emphasis should be on the decorator or decorators inside the suite, since those are the important modifiers to the function definition that follows. ... Readers are invited to read `the full response`_. .. _J2 proposal: http://www.aminus.org/rbre/python/pydec.html .. _rejected the proposal: http://mail.python.org/pipermail/python-dev/2004-September/048518.html .. _the full response: http://mail.python.org/pipermail/python-dev/2004-September/048518.html * Other forms There are plenty of other variants and proposals on `the wiki page`_. .. _the wiki page: http://www.python.org/moin/PythonDecorators Why @? ------ There is some history in Java using @ initially as a marker in `Javadoc comments`_ and later in Java 1.5 for `annotations`_, which are similar to Python decorators. The fact that @ was previously unused as a token in Python also means it's clear there is no possibility of such code being parsed by an earlier version of Python, leading to possibly subtle semantic bugs. It also means that ambiguity of what is a decorator and what isn't is removed. That said, @ is still a fairly arbitrary choice. Some have suggested using | instead. For syntax options which use a list-like syntax (no matter where it appears) to specify the decorators a few alternatives were proposed: ``[|...|]``, ``*[...]*``, and ``<...>``. .. _Javadoc comments: http://java.sun.com/j2se/javadoc/writingdoccomments/ .. _annotations: http://java.sun.com/j2se/1.5.0/docs/guide/language/annotations.html Current Implementation, History =============================== Guido asked for a volunteer to implement his preferred syntax, and Mark Russell stepped up and posted a `patch`_ to SF. This new syntax was available in 2.4a2. :: @dec2 @dec1 def func(arg1, arg2, ...): pass This is equivalent to:: def func(arg1, arg2, ...): pass func = dec2(dec1(func)) though without the intermediate creation of a variable named ``func``. The version implemented in 2.4a2 allowed multiple ``@decorator`` clauses on a single line. In 2.4a3, this was tightened up to only allowing one decorator per line. A `previous patch`_ from Michael Hudson which implements the list-after-def syntax is also still kicking around. .. _patch: http://www.python.org/sf/979728 .. _previous patch: http://starship.python.net/crew/mwh/hacks/meth-syntax-sugar-3.diff After 2.4a2 was released, in response to community reaction, Guido stated that he'd re-examine a community proposal, if the community could come up with a community consensus, a decent proposal, and an implementation. After an amazing number of posts, collecting a vast number of alternatives in the `Python wiki`_, a community consensus emerged (below). Guido `subsequently rejected`_ this alternate form, but added: In Python 2.4a3 (to be released this Thursday), everything remains as currently in CVS. For 2.4b1, I will consider a change of @ to some other single character, even though I think that @ has the advantage of being the same character used by a similar feature in Java. It's been argued that it's not quite the same, since @ in Java is used for attributes that don't change semantics. But Python's dynamic nature makes that its syntactic elements never mean quite the same thing as similar constructs in other languages, and there is definitely significant overlap. Regarding the impact on 3rd party tools: IPython's author doesn't think there's going to be much impact; Leo's author has said that Leo will survive (although it will cause him and his users some transitional pain). I actually expect that picking a character that's already used elsewhere in Python's syntax might be harder for external tools to adapt to, since parsing will have to be more subtle in that case. But I'm frankly undecided, so there's some wiggle room here. I don't want to consider further syntactic alternatives at this point: the buck has to stop at some point, everyone has had their say, and the show must go on. .. _Python wiki: http://www.python.org/moin/PythonDecorators .. _subsequently rejected: http://mail.python.org/pipermail/python-dev/2004-September/048518.html Community Consensus ------------------- This section documents the rejected J2 syntax, and is included for historical completeness. The consensus that emerged on comp.lang.python was the proposed J2 syntax (the "J2" was how it was referenced on the PythonDecorators wiki page): the new keyword ``using`` prefixing a block of decorators before the ``def`` statement. For example:: using: classmethod synchronized(lock) def func(cls): pass The main arguments for this syntax fall under the "readability counts" doctrine. In brief, they are: * A suite is better than multiple @lines. The ``using`` keyword and block transforms the single-block ``def`` statement into a multiple-block compound construct, akin to try/finally and others. * A keyword is better than punctuation for a new token. A keyword matches the existing use of tokens. No new token category is necessary. A keyword distinguishes Python decorators from Java annotations and .Net attributes, which are significantly different beasts. Robert Brewer wrote a `detailed proposal`_ for this form, and Michael Sparks produced `a patch`_. .. _detailed proposal: http://www.aminus.org/rbre/python/pydec.html .. _a patch: http://www.python.org/sf/1013835 As noted previously, Guido rejected this form, outlining his problems with it in `a message`_ to python-dev and comp.lang.python. .. _a message: http://mail.python.org/pipermail/python-dev/2004-September/048518.html Examples ======== Much of the discussion on ``comp.lang.python`` and the ``python-dev`` mailing list focuses on the use of decorators as a cleaner way to use the ``staticmethod()`` and ``classmethod()`` builtins. This capability is much more powerful than that. This section presents some examples of use. 1. Define a function to be executed at exit. Note that the function isn't actually "wrapped" in the usual sense. :: def onexit(f): import atexit atexit.register(f) return f @onexit def func(): ... Note that this example is probably not suitable for real usage, but is for example purposes only. 2. Define a class with a singleton instance. Note that once the class disappears enterprising programmers would have to be more creative to create more instances. (From Shane Hathaway on ``python-dev``.) :: def singleton(cls): instances = {} def getinstance(): if cls not in instances: instances[cls] = cls() return instances[cls] return getinstance @singleton class MyClass: ... 3. Add attributes to a function. (Based on an example posted by Anders Munch on ``python-dev``.) :: def attrs(**kwds): def decorate(f): for k in kwds: setattr(f, k, kwds[k]) return f return decorate @attrs(versionadded="2.2", author="Guido van Rossum") def mymethod(f): ... 4. Enforce function argument and return types. Note that this copies the func_name attribute from the old to the new function. func_name was made writable in Python 2.4a3:: def accepts(*types): def check_accepts(f): assert len(types) == f.func_code.co_argcount def new_f(*args, **kwds): for (a, t) in zip(args, types): assert isinstance(a, t), \ "arg %r does not match %s" % (a,t) return f(*args, **kwds) new_f.func_name = f.func_name return new_f return check_accepts def returns(rtype): def check_returns(f): def new_f(*args, **kwds): result = f(*args, **kwds) assert isinstance(result, rtype), \ "return value %r does not match %s" % (result,rtype) return result new_f.func_name = f.func_name return new_f return check_returns @accepts(int, (int,float)) @returns((int,float)) def func(arg1, arg2): return arg1 * arg2 5. Declare that a class implements a particular (set of) interface(s). This is from a posting by Bob Ippolito on ``python-dev`` based on experience with `PyProtocols`_. :: def provides(*interfaces): """ An actual, working, implementation of provides for the current implementation of PyProtocols. Not particularly important for the PEP text. """ def provides(typ): declareImplementation(typ, instancesProvide=interfaces) return typ return provides class IBar(Interface): """Declare something about IBar here""" @provides(IBar) class Foo(object): """Implement something here...""" .. _PyProtocols: http://peak.telecommunity.com/PyProtocols.html Of course, all these examples are possible today, though without syntactic support. Open Issues =========== 1. It's not yet certain that class decorators will be incorporated into the language at a future point. Guido expressed skepticism about the concept, but various people have made some `strong arguments`_ (search for ``PEP 318 -- posting draft``) on their behalf in ``python-dev``. It's exceedingly unlikely that class decorators will be in Python 2.4. .. _strong arguments: http://mail.python.org/pipermail/python-dev/2004-March/thread.html 2. The choice of the ``@`` character will be re-examined before Python 2.4b1. Copyright ========= This document has been placed in the public domain. .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End:

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RELEASED Python 2.4, alpha 3
by Anthony Baxter Sept. 3, 2004

Sept. 3, 2004

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On behalf of the Python development team and the Python community, I'm happy to announce the third alpha of Python 2.4. Python 2.4a3 is an alpha release. We'd greatly appreciate it if you could download it, kick the tires and let us know of any problems you find, but it is not suitable for production usage. ~ http://www.python.org/2.4 In this release we have PEP-292 string templates, a new syntax for multi-line imports, and a large number of other bug fixes and improvements. See either the highlights, the What's New in Python 2.4, or the detailed NEWS file -- all available from the Python 2.4 webpage. This will hopefully be the last alpha in the Python 2.4 cycle - a first beta will follow in a few weeks. Once the first beta is out, we're in feature-freeze mode - so if you've got new things you want in, make sure you hurry! Please log any problems you have with this release in the SourceForge bug tracker (noting that you're using 2.4a3): ~ http://sourceforge.net/bugs/?group_id=5470 Enjoy the new release, Anthony Anthony Baxter anthony(a)python.org Python Release Manager (on behalf of the entire python-dev team) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org iD8DBQFBOCz9Dt3F8mpFyBYRAmgqAJ42drhwIe3QLSx6WyUxOUPewUtX4QCgt5Wv mP4MfJRsXy6t0IcS6fY8Mmc= =efD5 -----END PGP SIGNATURE-----

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BayPIGgies: September 9, 7:30pm
by Aahz Sept. 2, 2004

Sept. 2, 2004

The next meeting of BayPIGgies will be Thurs September 9 at 7:30pm. It will feature a presentation about pyscheme by Danny Yoo. Haven't had time to update the web site, so here's Danny's summary: http://hkn.eecs.berkeley.edu/~dyoo/python/pyscheme/ o A quick introduction to Scheme, and how it's similar to Python. o A sketch of how pyscheme works. o Demo of the program itself. o Discussion on a core problem when implementing Scheme in Python: Recursion! - Python's recursion limit. - How to deal with it: bouncing functions on trampolines. o Maybe even continuations, if I haven't lost the audience by then. BayPIGgies meetings are in Stanford, California. For more information and directions, see http://www.baypiggies.net/ Before the meeting, some people will meet at 6pm for dinner in downtown Palo Alto. Ducky Sherwood is handling that; please send RSVPs to ducky(a)osafoundation.org by 4pm Thurs. Discussion of dinner plans is handled on the BayPIGgies mailing list. Advance notice: The October 14 meeting agenda has not been set. Please send e-mail to baypiggies(a)baypiggies.net if you want to make a presentation. -- Aahz (aahz(a)pythoncraft.com) <*> http://www.pythoncraft.com/ "To me vi is Zen. To use vi is to practice zen. Every command is a koan. Profound to the user, unintelligible to the uninitiated. You discover truth everytime you use it." --reddy(a)lion.austin.ibm.com

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ANN: PythonDoc 2.1 beta 1 (september 1, 2004)
by Fredrik Lundh Sept. 1, 2004

Sept. 1, 2004

PythonDoc is a documentation tool for Python, inspired by JavaDoc. Like JavaDoc, PythonDoc scans your Python code for doc comments, and generates API documentation in XML and HTML formats. Python- Doc supports basic JavaDoc tags like @param and @return, and adds a few Python-specific tags. You can use PythonDoc comments to describe module-level variables and constants, functions, classes, methods, and attributes. PythonDoc comes with a standard HTML generator, but you can plug in your own output handlers, or use XSTL or other tools to process the PythonDoc XML format. PythonDoc 2.1 is 2.0 plus support for Python 2.4 decorators, inline @link and @linkplain tags, and some bug fixes. See the README file for details. Brief description and examples (for an earlier alpha release): http://online.effbot.org/2003_10_01_archive.htm#pythondoc-20a1 Downloads: http://effbot.org/downloads#pythondoc http://effbot.org/downloads#elementtree Documentation: http://effbot.org/zone/pythondoc.htm Sample output (using the default "compact HTML" renderer): http://effbot.org/zone/pythondoc-compact.htm enjoy /F

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cx_Oracle 4.1 beta1
by Anthony Tuininga Sept. 1, 2004

Sept. 1, 2004

What is cx_Oracle? cx_Oracle is a Python extension module that allows access to Oracle and conforms to the Python database API 2.0 specifications with a few exceptions. Where do I get it? http://starship.python.net/crew/atuining What's new? 1) Added support for Python 2.4. In Python 2.4, the datetime module is used for both binding and fetching of date and timestamp data. In Python 2.3, objects from the datetime module can be bound but the This is internal datetime objects will be returned from queries. 2) Added pickling support for LOB and datetime data. 3) Fully qualified the table name that was missing in an alter table statement in the setup test script as noted by Marc Gehling. 4) Added a section allowing for the setting of the RPATH linker directive in setup.py as requested by Iustin Pop. 5) Added code to raise a programming error exception when an attempt is made to access a LOB locator variable in a subsequent fetch. 6) The username, password and dsn (tnsentry) are stored on the connection object when specified, regardless of whether or not a standard connection takes place. 7) Added additional module level constant called "LOB" as requested by Joseph Canedo. 8) Changed exception type to IntegrityError for constraint violations as requested by Joseph Canedo. 9) If scale and precision are not specified, an attempt is made to return a long integer as requested by Joseph Canedo. 10) Added workaround for Oracle bug which returns an invalid handle when the prepare call fails. Thanks to alantam(a)hsbc.com for providing the code that demonstrated the problem. 11) The cusor method arravar() will now accept the actual list so that it is not necessary to call cursor.arrayvar() followed immediately by var.setvalue(). 12) Fixed bug where attempts to execute the statement "None" with bind variables would cause a segmentation fault. 13) Added support for binding by position (paramstyle = "numeric"). 14) Removed memory leak created by calls to OCIParamGet() which were not mirrored by calls to OCIDescriptorFree(). Thanks to Mihai Ibanescu for pointing this out and providing a patch. 15) Added support for calling cursor.executemany() with statement None implying that the previously prepared statement ought to be executed. Thanks to Mihai Ibanescu for providing a patch. 16) Added support for rebinding variables when a subsequent call to cursor.executemany() uses a different number of rows. Thanks to Mihai Ibanescu for supplying a patch. 17) The microseconds are now displayed in datetime variables when nonzero similar to method used in the datetime module. 18) Added support for binary_float and binary_double columns in Oracle 10g. -- Anthony Tuininga anthony(a)computronix.com Computronix Distinctive Software. Real People. Suite 200, 10216 - 124 Street NW Edmonton, AB, Canada T5N 4A3 Phone: (780) 454-3700 Fax: (780) 454-3838 http://www.computronix.com

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