Mailman 3 August 2006 - Python-Dev

Re: [Python-Dev] Rounding float to int directly ...
by Nick Maclaren 02 Aug '06

02 Aug '06

Michael Chermside <mcherm(a)mcherm.com> wrote: > > > Decimal doesn't even help people who care about accuracy. > > Not true! The float class is incapable of maintaining 700 digits of > precision, but Decimal handles it just fine. (Why you would WANT > more than around 53 bits of precision is a different question, but > Decimal handles it.) Oh, yes, the CURRENT decimal class is potentially more accurate than the CURRENT floating class, but that has nothing to do with the intrinsic differences in the base. > > People who care about the accuracy of calculations prefer binary, > > as it is a more accurate model. > > Huh? That doesn't even make sense! A model is not inherently accurate > or inaccurate, it is only an accurate or inaccurate representation > of some "real" system. Neither binary nor decimal is a better > representation of either rational or real numbers, the first > candidates for "real" system I thought of. Financial accounting rules > tend to be based on paper-and-pencil calculations for which > decimal is usually a far better representation. > > If you had said that binary floats squeeze out more digits of > precision per bit of storage than decimal floats, or that binary > floats are faster because they are supported by specialized hardware, > then I'd go along, but they're not a "better model". No, that isn't true. The "wobbling precision" effect may be overstated, but is real, and gets worse the larger the base is. To the best of my knowledge, that is almost the only way in which binary is more accurate than decimal, in absolute terms, and it is a marginal difference. Note that I said "prefer", not "require" :-) For example, calculating the relative difference between two close numbers is sensitive to whether you are using the numbers in their normal or inverse forms (by a factor on N in base N), and this is a common cause of incorrect answers. A factor of 2 is better than one of 10. Regards, Nick Maclaren, University of Cambridge Computing Service, New Museums Site, Pembroke Street, Cambridge CB2 3QH, England. Email: nmm1(a)cam.ac.uk Tel.: +44 1223 334761 Fax: +44 1223 334679

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Weekly Python Patch/Bug Summary
by Kurt B. Kaiser 02 Aug '06

02 Aug '06

Patch / Bug Summary ___________________ Patches : 396 open ( -5) / 3354 closed (+12) / 3750 total ( +7) Bugs : 864 open (-32) / 6087 closed (+52) / 6951 total (+20) RFE : 226 open ( +2) / 234 closed ( +1) / 460 total ( +3) New / Reopened Patches ______________________ Move firewall warning to "about" menu (2006-07-26) http://python.org/sf/1529018 opened by Tal Einat Allowing multiple instances of IDLE with sub-processes (2006-07-26) http://python.org/sf/1529142 opened by Tal Einat Squeezer - squeeze large output in the interpreter (2006-07-27) http://python.org/sf/1529353 opened by Tal Einat More openbsd targets for ctypes (2006-07-27) CLOSED http://python.org/sf/1529514 opened by Thomas Heller test_defaultdict not integrated into test sute (2006-07-27) CLOSED http://python.org/sf/1529686 opened by iga Seilnacht misleading info about tarfile.py's "r|*" mode (2006-07-27) CLOSED http://python.org/sf/1529811 opened by Lars Gustäbel pydoc render_doc (2006-07-28) http://python.org/sf/1530482 opened by ganges master test_email_codecs not integrated into test sute (2006-07-27) CLOSED http://python.org/sf/1529686 reopened by zseil Fix __index__() clipping really big numbers (2006-07-29) http://python.org/sf/1530738 opened by Nick Coghlan "a + (2006-07-29) CLOSED http://python.org/sf/1531113 opened by Christopher Tur Lesniewski-Laas Tracing and profiling functions can cause hangs in threads (2006-07-31) http://python.org/sf/1531859 opened by Matt Fleming Support for case-insensitivity in string.Template (2006-07-25) CLOSED http://python.org/sf/1528167 reopened by whit537 Patches Closed ______________ Expose case-insensitivity of string.Template (2006-07-25) http://python.org/sf/1528167 closed by bwarsaw Fix for #1513611 and #1511497; xml.sax imports (2006-07-10) http://python.org/sf/1519796 closed by zseil More openbsd targets for ctypes (2006-07-27) http://python.org/sf/1529514 closed by theller test_defaultdict not integrated into test sute (2006-07-27) http://python.org/sf/1529686 closed by gbrandl misleading info about tarfile.py's "r|*" mode (2006-07-27) http://python.org/sf/1529811 closed by akuchling Support for PyGetSetDefs in pydoc, inspect, and types (2006-07-10) http://python.org/sf/1520294 closed by bwarsaw Fix socketmodule compile on NetBSD (2006-07-21) http://python.org/sf/1526460 closed by splitscreen test_email_codecs not integrated into test sute (2006-07-27) http://python.org/sf/1529686 closed by gbrandl Describe Py_DEBUG and friends... (2006-05-18) http://python.org/sf/1490989 closed by akuchling os.path.exists returns False if no permission (2004-11-17) http://python.org/sf/1068277 closed by akuchling "a + (2006-07-29) http://python.org/sf/1531113 closed by nnorwitz Fix zip file header format in zipfile.py (2003-07-30) http://python.org/sf/780595 closed by gbrandl Don't produce core file in test_subprocess.py (2006-07-11) http://python.org/sf/1520905 closed by akuchling New / Reopened Bugs ___________________ readline module description should mention raw_input() (2006-07-26) CLOSED http://python.org/sf/1529157 opened by Thom Harp possible bug in mystrtol.c with recent gcc (2006-07-13) CLOSED http://python.org/sf/1521947 reopened by nnorwitz unrelated variable messing up doctests (2006-07-26) CLOSED http://python.org/sf/1529297 reopened by macquigg BROWSER path with capital letters (2006-07-28) http://python.org/sf/1529655 opened by Ken McGaugh doc string of read-only properties (2006-07-27) CLOSED http://python.org/sf/1529717 opened by Michael Amrhein distutils regression related to Distribution.run_command (2006-07-27) CLOSED http://python.org/sf/1529871 opened by Collin Winter bz2 lib missing from source distribution (2006-07-27) CLOSED http://python.org/sf/1529998 opened by james yoo Mac Universal Build of Python confuses distutils (2006-07-28) http://python.org/sf/1530142 opened by Richard Jones ssl object documentation lacks a couple of methods (2006-07-28) CLOSED http://python.org/sf/1530382 opened by Lawrence Oluyede file.seek() influelce write() when opened with a+ mode (2006-07-12) http://python.org/sf/1521491 reopened by rudnik_lior ctypes build fails on Solaris 10 (2006-07-28) http://python.org/sf/1530448 opened by Skip Montanaro struct.pack raises TypeError where it used to convert (2006-07-28) http://python.org/sf/1530559 opened by Joe Wreschnig distutils doesn't notice --with-pydebug (2006-07-29) http://python.org/sf/1530959 opened by Collin Winter __weaklist__ in typeobject.c (2006-07-29) http://python.org/sf/1531003 opened by Fred L. Drake, Jr. Comman not allowed at the end of argument list for **argumen (2006-07-29) http://python.org/sf/1531016 opened by Roman Suzi Reflected (swapped) operations overridden by subclasses (2006-07-31) CLOSED http://python.org/sf/1531349 opened by Andrei Polushin format_exception raises if str(exception) raises (2006-07-30) http://python.org/sf/1531405 opened by Jp Calderone parsetok.c emits warnings by writing to stderr (2006-07-30) http://python.org/sf/1531415 opened by Jp Calderone Build fails on MacOSX with missing symbol (2006-07-31) http://python.org/sf/1531662 opened by gideon may HTTPSConnection request hangs (2006-07-31) http://python.org/sf/1531775 opened by Noam Taich subprocess.Popen(cmd, stdout=sys.stdout) fails (2006-07-31) http://python.org/sf/1531862 opened by John A Meinel SocketServer.TCPServer returns different ports (2006-07-31) http://python.org/sf/1531963 opened by hakker.de the csv module writes files that Excel sees as SYLK files (2006-08-01) http://python.org/sf/1532483 opened by Vincent Povirk incorrect behaviour of PyUnicode_EncodeMBCS? (2006-08-01) http://python.org/sf/1532726 opened by Jan-Willem Bugs Closed ___________ Build fails on OS X with case sensitive fs (2006-07-19) http://python.org/sf/1525447 closed by ronaldoussoren readline module description should mention raw_input() (2006-07-26) http://python.org/sf/1529157 closed by akuchling possible bug in mystrtol.c with recent gcc (2006-07-13) http://python.org/sf/1521947 closed by nnorwitz xml.sax.ParseException weirdness in python 2.5b1 (2006-06-27) http://python.org/sf/1513611 closed by fdrake Python 2.4c1 test_univnewlines.py fails within IDLE IDE (2004-11-19) http://python.org/sf/1069433 closed by kbk unrelated variable messing up doctests (2006-07-26) http://python.org/sf/1529297 closed by nnorwitz unrelated variable messing up doctests (2006-07-26) http://python.org/sf/1529297 closed by tim_one wrong handling of character buffers in stringobject (2006-07-01) http://python.org/sf/1515471 closed by nnorwitz xml.sax.expatreader is missing (2006-06-23) http://python.org/sf/1511497 closed by fdrake FTP modue functions are not re-entrant,give odd exceptions (2006-04-13) http://python.org/sf/1469557 closed by gbrandl turtle.py Docs still incomplete (2006-07-09) http://python.org/sf/1519571 closed by akuchling doc string of read-only properties (2006-07-27) http://python.org/sf/1529717 closed by gbrandl distutils regression related to Distribution.run_command (2006-07-27) http://python.org/sf/1529871 closed by pje bz2 lib missing from source distribution (2006-07-27) http://python.org/sf/1529998 closed by nnorwitz missing module names in email package (2005-12-27) http://python.org/sf/1391608 closed by bwarsaw mimetools message's To field can't be changed (2006-06-28) http://python.org/sf/1513913 closed by bwarsaw Docs on import of email.MIMExxx classes wrong (2006-05-04) http://python.org/sf/1481650 closed by bwarsaw email.Utils.py: UnicodeError in RFC2322 header (2006-01-24) http://python.org/sf/1414018 closed by bwarsaw ssl object documentation lacks a couple of methods (2006-07-28) http://python.org/sf/1530382 closed by akuchling new.function() docs out of date (2003-11-03) http://python.org/sf/835255 closed by gbrandl compiler module loses docstrings (2006-03-02) http://python.org/sf/1441397 closed by gbrandl inconsistency in help(set) (2006-01-25) http://python.org/sf/1414697 closed by akuchling xmlcore needs to be documented (2006-06-11) http://python.org/sf/1504456 closed by fdrake urllib2 data argument (2006-07-25) http://python.org/sf/1528258 closed by akuchling Finish PEP 343 terminology cleanup (2006-04-26) http://python.org/sf/1476845 closed by ncoghlan set documentation deficiencies (2006-02-10) http://python.org/sf/1429053 closed by akuchling Weakref types documentation bugs (2005-05-02) http://python.org/sf/1193966 closed by fdrake suspect documentation of operator.isNumberType (2004-01-17) http://python.org/sf/878908 closed by gbrandl Wrong documentation of __radd__ etc. (2004-08-03) http://python.org/sf/1002453 closed by gbrandl Documented grammar for List displays incorrect (testlist) (2004-11-22) http://python.org/sf/1071248 closed by gbrandl os.path.sameopenfile documentation wrong. (2004-08-03) http://python.org/sf/1002398 closed by gbrandl mode 't' not documented as posssible mode for file built-in (2005-12-15) http://python.org/sf/1381717 closed by gbrandl Strange os.path.exists() results with invalid chars (2005-04-30) http://python.org/sf/1193180 closed by gbrandl popen3 on windows loses environment variables (2005-01-13) http://python.org/sf/1101667 closed by gbrandl Reflected (swapped) operations overridden by subclasses (2006-07-30) http://python.org/sf/1531349 closed by gbrandl String Methods 2.3.6.1 not in TOC (2006-06-29) http://python.org/sf/1514540 closed by akuchling PEP 307 pickle extensions not documented (2004-07-04) http://python.org/sf/984952 closed by akuchling 4.2.6 (re) Examples: float regexp exponential on failure (2003-11-24) http://python.org/sf/848556 closed by akuchling pydoc fails on package in ZIP archive (2006-06-15) http://python.org/sf/1506951 closed by gbrandl Installing 2.3b2 on to non-system disk fails (2003-07-03) http://python.org/sf/764975 closed by ronaldoussoren New / Reopened RFE __________________ distutils 'register' command and windows home directories (2006-07-30) http://python.org/sf/1531505 opened by Josiah Carlson RFE Closed __________ No simple example for pickle (2006-03-01) http://python.org/sf/1441072 closed by gbrandl

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internal weakref API should be Py_ssize_t?
by Neal Norwitz 02 Aug '06

02 Aug '06

I'm wondering if the following change should be made to Include/weakrefobject.h: -PyAPI_FUNC(long) _PyWeakref_GetWeakrefCount(PyWeakReference *head); +PyAPI_FUNC(Py_ssize_t) _PyWeakref_GetWeakrefCount(PyWeakReference *head); And the 2 other files which use this (weakref obj and module). Should this be changed now, wait for 2.6, or not worry about it? n

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Strange memo behavior from cPickle
by Bruce Christensen 01 Aug '06

01 Aug '06

We seem to have stumbled upon some strange behavior in cPickle's memo use when pickling instances. Here's the repro: [mymodule.py] class C: def __getstate__(self): return ('s1', 's2', 's3') [interactive interpreter] Python 2.4.3 (#69, Mar 29 2006, 17:35:34) [MSC v.1310 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> import cPickle >>> import mymodule >>> class C: ... def __getstate__(self): return ('s1', 's2', 's3') ... >>> for x in mymodule.C(), C(): cPickle.dumps(x) ... "(imymodule\nC\np1\n(S's1'\nS's2'\np2\nS's3'\np3\ntp4\nb." "(i__main__\nC\np1\n(S's1'\nS's2'\nS's3'\ntp2\nb." >>> Note that the second and third strings in the instance's state are memoized in the first case, but not in the second. Any idea why this occurs (and why the first element is never memoized)? --Bruce

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clock_gettime() vs. gettimeofday()?
by skip＠pobox.com 01 Aug '06

01 Aug '06

This has probably been discussed before, however ... Is there any reason to use clock_gettime() in preference to gettimeofday() if it exists? It pretends to at least return seconds + nanoseconds, where gettimeofday() returns seconds + microseconds. Are there perhaps some platforms where it's possible to actually get more useful bits? On my Solaris 10/Intel desktop box clock_getres shows 0.01s resolution (not obviously better) while on a Linux box here it shows 0.001s resolution. Is that better than what gettimeofday() does? Skip

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Re: [Python-Dev] Rounding float to int directly ...
by Nick Maclaren 01 Aug '06

01 Aug '06

Raymond Hettinger <rhettinger(a)ewtllc.com> wrote: > > Hogwash.  The only issues with decimal are ease-of-use and speed.<br> I suggest that you get hold of a good 1960s or 1970s book on computer arithmetic, and read up about "wobbling precision". While it is not a big deal, it was regarded as such, and is important enough to cause significant numerical problems to the unwary - which means 99.99% of modern programmers :-( And, as I am sure that Aahz could point out, there are significant reliability issues concerned with frequent base changes where any loss of precision is unacceptable. Yes, it can always be done, but only a few people are likely to do it correctly in all cases. Regards, Nick Maclaren, University of Cambridge Computing Service, New Museums Site, Pembroke Street, Cambridge CB2 3QH, England. Email: nmm1(a)cam.ac.uk Tel.: +44 1223 334761 Fax: +44 1223 334679

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Re: [Python-Dev] Rounding float to int directly ...
by Nick Maclaren 01 Aug '06

01 Aug '06

Aahz <aahz(a)pythoncraft.com> wrote: > On Tue, Aug 01, 2006, M.-A. Lemburg wrote: > > > > You often have a need for controlled rounding when doing financial > > calculations or in situations where you want to compare two floats > > with a given accuracy, e.g. to work around rounding problems ;-) > > > > The usual approach is to use full float accuracy throughout the > > calculation and then apply rounding a certain key places. > > That's what Decimal() is for. Well, maybe. There are other approaches, too, and Decimal has its problems with that. In particular, when people need precisely defined decimal rounding, they ALWAYS need fixed-point and not floating-point. > (Note that I don't care all that much about round(), but I do think we > want to canonicalize Decimal() for all purposes in standard Python where > people care about accuracy. Additional float features can go into > NumPy.) Really? That sounds like dogma, not science. Decimal doesn't even help people who care about accuracy. At most (and with the reservation mentioned above), it means that you can can map external decimal formats to internal ones without loss of precision. Not a big deal, as there ARE no requirements for doing that for floating-point, and there are plenty of other solutions for fixed-point. People who care about the accuracy of calculations prefer binary, as it is a more accurate model. That isn't a big deal, either. Regards, Nick Maclaren, University of Cambridge Computing Service, New Museums Site, Pembroke Street, Cambridge CB2 3QH, England. Email: nmm1(a)cam.ac.uk Tel.: +44 1223 334761 Fax: +44 1223 334679

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Which version of distutils to ship with Python 2.5?
by Collin Winter 01 Aug '06

01 Aug '06

Is it intentional that Python 2.5 is (currently) shipping with distutils 2.4.0, while Python 2.4 (at least 2.4.1, 2.4.2 and 2.4.3) shipped with distutils 2.4.1? Judging from my own tests, distutils 2.4.1 fixed several bugs that some of my test suites depend on (the fixes, not the bugs ; ). Thanks, Collin Winter

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