Mailman 3 March 2009 - Python-Dev

Grammar for plus and minus unary ops
by Jared Grubb 27 Mar '09

27 Mar '09

I was recently reviewing some Python code for a friend who is a C++ programmer, and he had code something like this: def foo(): try = 0 while try<MAX: ret = bar() if ret: break ++try I was a bit surprised that this was syntactically valid, and because the timeout condition only occurred in exceptional cases, the error has not yet caused any problems. It appears that the grammar treats the above example as the unary + op applied twice: u_expr ::= power | "-" u_expr | "+" u_expr | "\~" u_expr Playing in the interpreter, expressions like "1+++++++++5" and "1+-+- +-+-+-+-5" evaluate to 6. I'm not a EBNF expert, but it seems that we could modify the grammar to be more restrictive so the above code would not be silently valid. E.g., "++5" and "1+++5" and "1+-+5" are syntax errors, but still keep "1++5", "1+-5", "1-+5" as valid. (Although, '~' throws in a kink... should '~-5' be legal? Seems so...) Jared

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"setuptools has divided the Python community"
by Olemis Lang 27 Mar '09

27 Mar '09

On Fri, Mar 27, 2009 at 2:27 PM, Eric Smith <eric(a)trueblade.com> wrote: > Olemis Lang wrote: >>> >>> I also think the feature should go. If you want functionality that's so >>> difficult to provide when you install as a zip file, the answer is not to >>> make things more complex, but to not install as zip files. >>> >> >> What about environments like Google App Engine ? I mean, AFAIK using >> ZIP files is the *official* solution to meet some quotas & >> requirements ... CMIIW anyway ... >> >> I mean, for example: what if someone writes an app containing >> resources like message catalogs for i18n, uploads it to GAE using ZIP >> files and still wants to use the MO files (i.e. resources) for >> translation (i.e. for anything else ...) ... Hmmmm ? > > I mentioned yesterday (in the language summit) that we really need to get > all the requirements together before we start any work. I fear that there > are many hidden requirements (or ones that I'm personally not aware of, at > least). I don't know gettext well enough give an answer yet. > > Perhaps it is not necessary ... i18n was only a motivation to establish a concrete (... *very real* & *no more choices* ...) use case. The same could be said like this : «What if someone writes an app containing many (... *A LOT OF* ...) resource files, uploads it to GAE using ZIP files, and still wants to use them for anything he/she wants ... Hmmmm ?» ;o) -- Regards, Olemis. Blog ES: http://simelo-es.blogspot.com/ Blog EN: http://simelo-en.blogspot.com/ Featured article: Comandos : Pipe Viewer ... ¿Qué está pasando por esta tubería?

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GPython?
by Terry Reedy 27 Mar '09

27 Mar '09

An ars technica articla just linked to in a python-list post http://arstechnica.com/open-source/news/2009/03/google-launches-project-to-… calls the following project "Google launched" http://code.google.com/p/unladen-swallow/wiki/ProjectPlan (Though the project page does not really claim that.) I am sure some people here might find this interesting. I'd love to have a faster CPython, but this note: "Will probably kill Python Windows support (for now)." would kill merger back into mainline (for now) without one opposing being 'conservative'. If one adds type annotations so that values can be unboxed, would not Cython, etc, do even better for speedup? tjr

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Summary of Python tracker Issues
by Python tracker 27 Mar '09

27 Mar '09

ACTIVITY SUMMARY (03/20/09 - 03/27/09) Python tracker at http://bugs.python.org/ To view or respond to any of the issues listed below, click on the issue number. Do NOT respond to this message. 2395 open (+33) / 15008 closed (+21) / 17403 total (+54) Open issues with patches: 845 Average duration of open issues: 661 days. Median duration of open issues: 400 days. Open Issues Breakdown open 2357 (+33) pending 38 ( +0) Issues Created Or Reopened (55) _______________________________ float compared to decimal is silently incorrect. 03/21/09 http://bugs.python.org/issue2531 reopened marketdickinson patch, easy multiprocessing won't work with Tkinter (under Linux) 03/20/09 http://bugs.python.org/issue5527 created akineko Unable to launch IDLE on Windows 03/20/09 CLOSED http://bugs.python.org/issue5528 created croy Backport sys module docs involving import to 2.7 03/21/09 http://bugs.python.org/issue5529 created brett.cannon datetime class names should obey PEP 8 CapWords convention 03/21/09 CLOSED http://bugs.python.org/issue5530 created jess.austin patch unittest: allow failures in tearDown method 03/21/09 CLOSED http://bugs.python.org/issue5531 created gfxmonk patch imap usage in itertools unique_justseen recipe 03/21/09 CLOSED http://bugs.python.org/issue5532 created mnewman unittest can't deal with packages 03/21/09 http://bugs.python.org/issue5533 created Indy Decimal __format__ reverses meaning of '<' and '>' alignment spe 03/22/09 CLOSED http://bugs.python.org/issue5534 created donodonnell json custom encoder not fully functionnal 03/22/09 CLOSED http://bugs.python.org/issue5535 created phanser urllib: urlretrieve() does not close file objects on failure 03/22/09 CLOSED http://bugs.python.org/issue5536 created petr.dolezal LWPCookieJar cannot handle cookies with expirations of 2038 or g 03/22/09 http://bugs.python.org/issue5537 created hollec tearDown in unittest should be executed regardless of result in 03/22/09 CLOSED http://bugs.python.org/issue5538 created yaneurabeya needs review open documentation unclear 03/23/09 CLOSED http://bugs.python.org/issue5539 created LambertDW "file objects" in python 3 tutorial 03/23/09 http://bugs.python.org/issue5540 created LambertDW File's current position inconsistent with 'a+' mode 03/23/09 CLOSED http://bugs.python.org/issue5541 created ebfe Socket is closed prematurely in httplib, if server sends respons 03/23/09 http://bugs.python.org/issue5542 created jasondavies sys.last_type missing 03/23/09 CLOSED http://bugs.python.org/issue5543 created brtzsnr test_fileio fails on windows MSVC Assertion 03/23/09 http://bugs.python.org/issue5544 created andreas.schawo multiprocessing: switch to autoconf detection of platform values 03/23/09 http://bugs.python.org/issue5545 created jnoller patch PyDict_SetItemString mentions PyString_FromString which does not 03/23/09 CLOSED http://bugs.python.org/issue5546 created stutzbach The Py_InitModule functions no longer exist, but remain in the d 03/23/09 CLOSED http://bugs.python.org/issue5547 created stutzbach In the tutorial, PyMODINIT_FUNC is shown as having a return type 03/23/09 http://bugs.python.org/issue5548 created stutzbach PyModule_Create and PyModuleDef are undocumented 03/23/09 CLOSED http://bugs.python.org/issue5549 created stutzbach urllib2 use of opener.addheaders 03/24/09 http://bugs.python.org/issue5550 created cocobear os.path.ismount takes a cross-device symlink for a mountpoint 03/24/09 http://bugs.python.org/issue5551 created jae With invalid FD, os.device_encoding() returns None under Linux b 03/24/09 CLOSED http://bugs.python.org/issue5552 created pitrou Py_LOCAL_INLINE(type) doesn't actually inline except using MSC 03/24/09 http://bugs.python.org/issue5553 created stutzbach file.read() doesn't read the whole file 03/24/09 CLOSED http://bugs.python.org/issue5554 created Ultrasick optparse 03/24/09 http://bugs.python.org/issue5555 created ajs interactive interpreter, source encoding 03/24/09 http://bugs.python.org/issue5556 created jmfauth Byte-code compilation uses excessive memory 03/24/09 http://bugs.python.org/issue5557 created goddard Python 3.0.1 Mac OS X install image ReadMe file is incorrect 03/24/09 http://bugs.python.org/issue5558 created xdcdx IDLE Output Window 's goto fails when path has spaces 03/25/09 http://bugs.python.org/issue5559 created ccanepa help() no longer reports module docstrings 03/25/09 CLOSED http://bugs.python.org/issue5560 created debatem1 platform.python_version_tuple returns tuple of ints, should be s 03/25/09 CLOSED http://bugs.python.org/issue5561 created Larry Hastings Locale-based date formatting crashes on non-ASCII data 03/25/09 http://bugs.python.org/issue5562 created pitrou Document bdist_msi 03/25/09 http://bugs.python.org/issue5563 created bethard os.symlink/os.link docs should say old/new, not src/dst 03/26/09 http://bugs.python.org/issue5564 created Rhamphoryncus Strange behavior when I logout() with IMAP4_SSL 03/26/09 http://bugs.python.org/issue5565 created toelke Minor error in document of PyLong_AsSsize_t 03/26/09 http://bugs.python.org/issue5566 created bhy Operators in operator module don't work with keyword arguments 03/26/09 http://bugs.python.org/issue5567 created leonidas self.writer.closed() extraneous parens in BufferedRWPair of io m 03/26/09 CLOSED http://bugs.python.org/issue5568 created jimo555 Issue in transparency in top level tk window(python) on MAC 03/26/09 CLOSED http://bugs.python.org/issue5569 created YMohan Bus error when calling .poll() on a closed Connection from multi 03/26/09 http://bugs.python.org/issue5570 created amacleod new "TestCase.skip" method causes all tests to skip under trial 03/26/09 CLOSED http://bugs.python.org/issue5571 created glyph distutils ignores the LIBS configure env var 03/26/09 http://bugs.python.org/issue5572 created collinwinter patch, patch, needs review multiprocessing Pipe poll() and recv() semantics. 03/26/09 http://bugs.python.org/issue5573 created mallyvai multiprocessing queues.py doesn't include JoinableQueue in its _ 03/26/09 http://bugs.python.org/issue5574 created mallyvai Add env vars for controlling building sqlite, hashlib and ssl 03/26/09 http://bugs.python.org/issue5575 created collinwinter patch, patch, needs review Don't use PyLong_SHIFT with _PyLong_AsScaledDouble() 03/27/09 http://bugs.python.org/issue5576 created haypo patch yield in iterators 03/27/09 http://bugs.python.org/issue5577 created qwjqwj unqualified exec in class body 03/27/09 http://bugs.python.org/issue5578 created fijal patch Display for OrderedDict 03/27/09 http://bugs.python.org/issue5579 created tweiler Strange error message in Python/getargs.c 03/27/09 http://bugs.python.org/issue5580 created mishok13 Issues Now Closed (60) ______________________ asyncore loop lacks timers and work tasks 415 days http://bugs.python.org/issue2006 intgr Traceback changed in 2.6 for unhashable objects 364 days http://bugs.python.org/issue2485 benjamin.peterson Hang when calling get() on an empty queue in the queue module 281 days http://bugs.python.org/issue3138 tazle improve linecache: reuse tokenize.detect_encoding() and io.open( 103 days http://bugs.python.org/issue4016 benjamin.peterson patch float(0.0) singleton 169 days http://bugs.python.org/issue4024 tjreedy patch Make multiprocessing compatible with Python 2.4 and 2.5 149 days http://bugs.python.org/issue4208 haypo patch, patch Classify language vs. impl-detail tests, step 1 147 days http://bugs.python.org/issue4242 benjamin.peterson patch, patch Segfault in stringobject.c 125 days http://bugs.python.org/issue4358 haypo compile() doesn't ignore the source encoding when a string is pa 104 days http://bugs.python.org/issue4626 haypo patch, needs review GC optimization: don't track simple tuples and dicts 96 days http://bugs.python.org/issue4688 pitrou patch PyFile_FromFd() doesn't set the file name 86 days http://bugs.python.org/issue4762 haypo difflib 77 days http://bugs.python.org/issue4889 jackdied Windows installer Quad processor issues 69 days http://bugs.python.org/issue4911 loewis tarfile loops forever on broken input 55 days http://bugs.python.org/issue5068 lars.gustaebel import tkinter library Visual C++ Concepts:C Run-Time Error R603 58 days http://bugs.python.org/issue5090 amaury.forgeotdarc Printing Unicode chars from the interpreter in a non-UTF8 termin 55 days http://bugs.python.org/issue5110 haypo patch Space character returns false from isprintable() method 53 days http://bugs.python.org/issue5126 benjamin.peterson patch struct.calcsize('cd') returns 16 instead of 9 51 days http://bugs.python.org/issue5145 haypo Add KOI8-RU as a known encoding 44 days http://bugs.python.org/issue5214 lemburg json needs object_pairs_hook 23 days http://bugs.python.org/issue5381 cheeaun patch urllib.response.addinfourl does not support __exit__ 22 days http://bugs.python.org/issue5418 jhylton test_httpservers on Debian Testing 16 days http://bugs.python.org/issue5435 facundobatista Streamline integer division 5 days http://bugs.python.org/issue5512 haypo patch "What's New" should say VERY CLEARLY that the type file is gone 4 days http://bugs.python.org/issue5513 benjamin.peterson cPickle produces inconsistent output 1 days http://bugs.python.org/issue5518 loewis refactor test_datetime.py 5 days http://bugs.python.org/issue5520 jess.austin patch Unable to launch IDLE on Windows 6 days http://bugs.python.org/issue5528 amaury.forgeotdarc datetime class names should obey PEP 8 CapWords convention 4 days http://bugs.python.org/issue5530 gvanrossum patch unittest: allow failures in tearDown method 1 days http://bugs.python.org/issue5531 brett.cannon patch imap usage in itertools unique_justseen recipe 1 days http://bugs.python.org/issue5532 benjamin.peterson Decimal __format__ reverses meaning of '<' and '>' alignment spe 0 days http://bugs.python.org/issue5534 marketdickinson json custom encoder not fully functionnal 1 days http://bugs.python.org/issue5535 bob.ippolito urllib: urlretrieve() does not close file objects on failure 0 days http://bugs.python.org/issue5536 benjamin.peterson tearDown in unittest should be executed regardless of result in 1 days http://bugs.python.org/issue5538 yaneurabeya needs review open documentation unclear 0 days http://bugs.python.org/issue5539 benjamin.peterson File's current position inconsistent with 'a+' mode 1 days http://bugs.python.org/issue5541 loewis sys.last_type missing 0 days http://bugs.python.org/issue5543 benjamin.peterson PyDict_SetItemString mentions PyString_FromString which does not 0 days http://bugs.python.org/issue5546 benjamin.peterson The Py_InitModule functions no longer exist, but remain in the d 0 days http://bugs.python.org/issue5547 benjamin.peterson PyModule_Create and PyModuleDef are undocumented 0 days http://bugs.python.org/issue5549 stutzbach With invalid FD, os.device_encoding() returns None under Linux b 0 days http://bugs.python.org/issue5552 pitrou file.read() doesn't read the whole file 0 days http://bugs.python.org/issue5554 Ultrasick help() no longer reports module docstrings 1 days http://bugs.python.org/issue5560 amaury.forgeotdarc platform.python_version_tuple returns tuple of ints, should be s 0 days http://bugs.python.org/issue5561 lemburg self.writer.closed() extraneous parens in BufferedRWPair of io m 1 days http://bugs.python.org/issue5568 amaury.forgeotdarc Issue in transparency in top level tk window(python) on MAC 1 days http://bugs.python.org/issue5569 amaury.forgeotdarc new "TestCase.skip" method causes all tests to skip under trial 0 days http://bugs.python.org/issue5571 benjamin.peterson unittest.py patch: add skipped test functionality 1641 days http://bugs.python.org/issue1034053 benjamin.peterson patch os.times() is bogus 1628 days http://bugs.python.org/issue1040026 loewis patch csv Sniffer returns bad dialect? 1481 days http://bugs.python.org/issue1157169 skip.montanaro Call by object reference sometimes call by value 1278 days http://bugs.python.org/issue1296434 benjamin.peterson set.__getstate__ is not overriden 1254 days http://bugs.python.org/issue1326448 rhettinger shutils cannot copy owner 1209 days http://bugs.python.org/issue1368091 ajaksu2 email.Utils.parseaddr() gives arcane result 1157 days http://bugs.python.org/issue1409460 ajaksu2 Popened file object close hangs in latest Cygwin update 1155 days http://bugs.python.org/issue1413379 sferic CSV Sniffer fails to report mismatch of column counts 1135 days http://bugs.python.org/issue1431091 skip.montanaro sys.getrefcount should be in gc 1031 days http://bugs.python.org/issue1494595 benjamin.peterson C API to retain GIL during Python Callback 1031 days http://bugs.python.org/issue1497532 benjamin.peterson random.choice(setinstance) fails 936 days http://bugs.python.org/issue1551113 tim_one unittest documentation is incomplete 740 days http://bugs.python.org/issue1681984 haypo Top Issues Most Discussed (10) ______________________________ 16 tearDown in unittest should be executed regardless of result in 1 days closed http://bugs.python.org/issue5538 15 test_fileio fails on windows MSVC Assertion 4 days open http://bugs.python.org/issue5544 10 float compared to decimal is silently incorrect. 6 days open http://bugs.python.org/issue2531 8 yield in iterators 0 days open http://bugs.python.org/issue5577 8 unittest: allow failures in tearDown method 1 days closed http://bugs.python.org/issue5531 6 multiprocessing: switch to autoconf detection of platform value 4 days open http://bugs.python.org/issue5545 6 indentation in IDLE 2.6 different from IDLE 2.5, 2.4 or vim 53 days open http://bugs.python.org/issue5129 6 compile() doesn't ignore the source encoding when a string is p 104 days closed http://bugs.python.org/issue4626 6 32-bits unsigned user/group identifier 109 days open http://bugs.python.org/issue4591 5 Byte-code compilation uses excessive memory 3 days open http://bugs.python.org/issue5557

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"yield" in list comprehensions
by Antoine Pitrou 27 Mar '09

27 Mar '09

Hello, Just for the record, I thought I'd point out this slightly exotic and funny incompatibility between 2.x and py3k. This is due to the fact that list comprehensions now live in their own frame, so a "yield" expression inside a list comprehension turns the comprehension itself into a generator (rather than the enclosing function). http://bugs.python.org/issue5577 Regards Antoine.

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Re: [Python-Dev] suggestion for try/except program flow
by Hrvoje Niksic 27 Mar '09

27 Mar '09

Mark Donald wrote: > Thanks for the idea, but I believe it has a different outcome. You'd > have to copy the generic handler into an except clause to get exactly > the behaviour I'm looking for, which is worse than nesting the try > blocks Then simply change Exception to BaseException. Since all exceptions should derive from BaseException, there should be no difference between that and a bare "except:" clause.

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"setuptools has divided the Python community"
by Olemis Lang 27 Mar '09

27 Mar '09

On Fri, Mar 27, 2009 at 5:22 AM, Paul Moore <p.f.moore(a)gmail.com> wrote: > 2009/3/27 Guido van Rossum <guido(a)python.org>: >> - keep distutils, but start deprecating certain higher-level >> functionality in it (e.g. bdist_rpm) >> - don't try to provide higher-level functionality in the stdlib, but >> instead let third party tools built on top of these core APIs compete > > Please don't move bdist_wininst out of the core, though! > > I'd argue that Windows is a special case, as many Windows users don't > have the ability to build their own extensions, Hmmmm ... what about devs (me?) trying to build installers for multiple platforms being in a single OS (let's say Ubuntu ...) ? IMO in this case where policies are unique for a particular OS-flavour (deb, rpms, and so on ...) ... there should be a single way to package your app and to conform to the standards agreed by distros (e.g. Debian) and maintainers ... isnt it enough std to be in stdlib ? I'd really like to have those (... at least the most influential systems ... rpm, debs, and maybe two or three more that I'm missing here ...) Indeed I'd like to know the arguments behind «deprecating certain higher-level functionality in it (e.g. bdist_rpm)» BTW ... perhaps they'r self-explanatory and therefore I should not be asking this at all ... :P -- Regards, Olemis. Blog ES: http://simelo-es.blogspot.com/ Blog EN: http://simelo-en.blogspot.com/ Featured article: Comandos : Pipe Viewer ... ¿Qué está pasando por esta tubería?

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Re: [Python-Dev] suggestion for try/except program flow
by Hrvoje Niksic 27 Mar '09

27 Mar '09

Mark Donald wrote: > I frequently have this situation: > > try: > try: > raise Thing > except Thing, e: > # handle Thing exceptions > raise > except: > # handle all exceptions, including Thing How about: try: ... code that can raise Thing or another exception ... except Exception, e: if isinstance(e, Thing): # handle thing # generic exception handling

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return from a generator [was:PEP 380 (yield from a subgenerator) comments]
by Jim Jewett 27 Mar '09

27 Mar '09

On Thu, Mar 26, 2009 at 4:19 PM, P.J. Eby wrote: >> What I don't like is the confusion of adding "return values" to generators, >> at least using the 'return' statement. At Fri Mar 27 04:39:48 CET 2009, Guido van Rossum replied: > I'm +1 on "yield from" and +0 on return values in generators. > def g(): > yield 42 > return 43 > for x in g(): > print x # probably expected to print 42 and then 43 I still don't see why it needs to be a return statement. Why not make the intent of g explicit, by writing either def g(): yield 42 yield 43 or def g(): yield 42 raise StopIteration(43) -jJ

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Re: [Python-Dev] PEP 380 (yield from a subgenerator) comments
by P.J. Eby 27 Mar '09

27 Mar '09

At 09:24 PM 3/25/2009 -0700, Guido van Rossum wrote: >ISTR that the motivation for adding new syntax is that the best you >can do using a trampoline library is still pretty cumbersome to use >when you have to write a lot of tasks and subtasks, and when using >tasks is just a tool for getting things done rather than an end goal >in itself. I agree that the motivation and the comparison should be >added to the PEP (perhaps moving the trampoline sample >*implementation* to a reference or an appendix, since it is only the >appearance of the trampoline-*using* code that matters). In particular, it should explain why these choices are so costly as to justify new syntax and a complex implementation: * decorator clearly identifying intent to create a task vs. no indication of task-ness * "yield Return(value)" vs. "return value" * "result = yield subgenerator()" vs. "result = yield from subgenerator()" Especially since the first two differences arguably make the non-"yield from" code clearer, and the third makes it more compact. >with judicious use of decorators and helper classes you can get a >reasonable approximation, and I think Twisted uses something like >this, so it's not just theory. I think the best you can do without new >syntax though is still pretty cumbersome and brittle, which is why I >have encouraged your PEP. On the "cumbersome" side, there are only three differences, as I've shown above... and one of them uses less syntax than the PEP. I'm not sure what you mean by brittle. Twisted and PEAK have both had generator-based tasks for ages, and have been used in production for years, even before generators had send()/throw() -- the addition of yield expressions made it possible to get rid of the one previous brittleness, where you needed to do things like: yield subgenerator(); result = resume() in order to pass values or exceptions in. Since send()/throw() was added, the need to call a function after each yield was eliminated, at least from PEAK and my newer Trellis library; haven't looked at Twisted's tasks in a while. I believe there are other generator-based task libraries available on PyPI, but can't comment on their robustness. (The existence of throw(), by the way, makes it possible to produce tracebacks that look *exactly* as if you had called a series of functions, rather than iterating over a bunch of generators. The sample code I gave should do this correctly, as it was created by yanking out working, tested code from my Trellis library, and cutting out all the Trellis-specific bits.) If someone can find any semantic differences between the code I posted and the yield-from proposal (apart from the absence of the "for x in y: yield x" part of the functionality), I'd like to know about it... and it should go in the PEP.

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Python-Dev March 2009