[issue7117] Backport py3k float repr to trunk
Amaury Forgeot d'Arc amaur...@gmail.com added the comment: I've filed issue12450 to track this last idea. -- nosy: +amaury.forgeotdarc ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Changes by STINNER Victor victor.stin...@haypocalc.com: -- nosy: +haypo ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Michael Foord mich...@voidspace.org.uk added the comment: Wondered if you guys had heard of some recent advances in the state of the art in this field. I'm sure you have, but thought I'd link it here anywhere. Quote taken from this article (which links to relevant papers): http://www.serpentine.com/blog/2011/06/29/here-be-dragons-advances-in-problems-you-didnt-even-know-you-had/ In 2010, Florian Loitsch published a wonderful paper in PLDI, Printing floating-point numbers quickly and accurately with integers, which represents the biggest step in this field in 20 years: he mostly figured out how to use machine integers to perform accurate rendering! Why do I say mostly? Because although Loitsch's Grisu3 algorithm is very fast, it gives up on about 0.5% of numbers, in which case you have to fall back to Dragon4 or a derivative. If you're a language runtime author, the Grisu algorithms are a big deal: Grisu3 is about 5 times faster than the algorithm used by printf in GNU libc, for instance. A few language implementors have already taken note: Google hired Loitsch, and the Grisu family acts as the default rendering algorithms in both the V8 and Mozilla Javascript engines (replacing David Gay's 17-year-old dtoa code). Loitsch has kindly released implementations of his Grisu algorithms as a library named double-conversion. -- nosy: +michael.foord ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: Hadn't seen that. Interesting! -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Raymond Hettinger raymond.hettin...@gmail.com added the comment: Thanks for the link :-) -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: Thanks, Eric. The only remaining documentation issues I'm aware of are in Doc/tutorial/floatingpoint.rst. I think Raymond is going to update this to match the py3k version. I'll call this done, then! Thanks for all your help. -- resolution: - accepted stage: - committed/rejected status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: Thanks for tackling the last few bits, Mark. I think we're done, although I admit I haven't verified what state the documentation is in. I suggest we close this issue and if any problems occur open them as new issues. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r76465 removes the fixed-length buffer for formatting floats, hence removes the restriction on the precision. This should make removal of the %f - %g switch straightforward. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r76474: Remove %f - %g switch. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: Short float repr is now enabled in r76379. Misc/NEWS entries added/updated in r76411. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r76373: Backport round. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: Here's a patch for correctly-rounded round in trunk. This patch doesn't change the rounding behaviour between 2.6 and 2.7: it's still doing round-half-away-from-zero instead of round-half-even. It was necessary to detect and treat halfway cases specially to make this work. Removing this special case code would be easy, so we can decide later whether it's worth changing round to do round-half-to-even for 2.7. I want to let this sit for a couple of days before I apply it. -- keywords: +patch Added file: http://bugs.python.org/file15254/round_fixup.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r75979: Deprecate PyOS_ascii_atof and PyOS_ascii_strtod; document PyOS_double_to_string. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: The next job is to deprecate PyOS_ascii_atof and PyOS_ascii_strtod, I think. I'll get to work on that. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: r75913: Fix _json.c to use PyOS_string_to_double. Change made after consulting with Bob Ippolito. This completes the removal of calls to PyOS_ascii_strtod. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: r75743: Fix cPickle.c to use PyOS_string_to_double. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: r75745: Fix stropmodule.c to use PyOS_string_to_double. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: r75824: Fix ast.c to use PyOS_string_to_double. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: r75846: Fix marshal.c to use PyOS_string_to_double. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r75720: Backport py3k version of pystrtod.c to trunk. There are still some (necessary) differences between the two versions, which should become unnecessary once everything else is hooked up. The differences should be re-examined later. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: [Eric, on removing f to g conversions] Should we also do that as part of this exercise? Or should it be another issue, or not done at all? I'd definitely like to remove the f to g conversion in trunk. I don't see any great need to open a separate issue for that. (Was there one already for the py3k removal?) -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: Found it: issue #5859 was opened for the removal of the f - g conversion in py3k. We could just add a note to that issue. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r75730: backport pystrtod.h r75731: Fix floatobject.c to use PyOS_string_to_double. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r75739: Fix complexobject.c to use PyOS_string_to_double. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: Some key revision numbers from the py3k short float repr, for reference: r71663: include Gay's code, build and configure fixes r71723: backout SSE2 detection code added in r71663 r71665: rewrite of float formatting code to use Gay's code Backported most of r71663 and r71723 to trunk in: r75651: Add dtoa.c, dtoa.h, update license. r75658: configuration changes - detect float endianness, add functions to get and set x87 control word, and determine when short float repr can be used. Significant changes from r71663 not yet included: * Misc/NEWS update * Lib/test/formatfloat_testcases.txt needs updating to match py3k. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r75666: Add sys.float_repr_style attribute. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment: r75672: temporarily disable the short float repr while we're putting the pieces in place. When testing, the disablement can be disabled (hah) by defining the PY_SHORT_FLOAT_REPR preprocessor symbol, e.g. (on Unix) with CC='gcc -DPY_SHORT_FLOAT_REPR' ./configure make -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: I think the next step on my side is to remove _PyOS_double_to_string, and make all of the internal code call PyOS_double_to_string. The distinction is that _PyOS_double_to_string gets passed a buffer and length, but PyOS_double_to_string returns allocated memory that must be freed. David Gay's code (_Py_dg_dtoa) returns allocated memory, so that's the easiest interface to propagate internally. That's the approach we used in the py3k branch. I'll start work on it. So Mark's work should be mostly config stuff and hooking up Gay's code to PyOS_double_to_string. I think it will basically match the py3k version. The existing _PyOS_double_to_string will become the basis for the fallback code for use when PY_NO_SHORT_FLOAT_REPR is defined (and it will then be renamed PyOS_double_to_string and have its signature changed to match). -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Mark Dickinson dicki...@gmail.com added the comment:
One issue occurs to me: should the backport change the behaviour of the
round function?
In py3k, round consistently uses round-half-to-even for halfway cases.
In trunk, round semi-consistently uses round-half-away-from-zero (and
this is documented). E.g., round(1.25, 1) will give 1.2 in py3k and
(usually) 1.3 in trunk.
I definitely want to use Gay's code for round in 2.7, since having round
work sensibly is part of the motivation for the backport in the first
place. But this naturally leads to a round-half-to-even version of
round, since the Python-adapted version of Gay's code isn't capable of
doing anything other than round-half-to-even at the moment.
Options:
(1) change round in 2.7 to do round-half-to-even. This is easy,
natural, and means that round will agree with float formatting
(which does round-half-to-even in both py3k and trunk). But it
may break existing applications. However: (a) those applications
would need fixing anyway to work with py3k, and (b) I have little
sympathy for people depending on behaviour of rounding of
*binary* floats for halfway *decimal* cases. (Decimal is another
matter, of course: there it's perfectly reasonable to expect
guaranteed rounding behaviour.)
It's more complicated than that, though, since if rounding
becomes round-half-to-even for floats, it should also change
for integers, Fractions, etc.
(2) have round stick with round-half-away-from-zero. This may be
awkward to implement (though I have some half-formed ideas about
how to make it work), and would lead to round occasionally not
agreeing with float formatting. For example:
'{0:.1f}'.format(1.25)
'1.2'
round(1.25, 1)
1.3
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[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: Adding tim_one as nosy. He'll no doubt have an opinion on rounding. And hopefully he'll share it! -- nosy: +tim_one ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Eric Smith e...@trueblade.com added the comment: Another thing to consider is that in py3k we removed all conversions of converting 'f' to 'g', such as this, from Objects/unicodeobject.c: if (type == 'f' fabs(x) = 1e50) type = 'g'; Should we also do that as part of this exercise? Or should it be another issue, or not done at all? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
Raymond Hettinger rhettin...@users.sourceforge.net added the comment: +1 on backporting the 'f' and 'g' work also. We will be well served by getting the two code bases ins-sync with one another. Eliminating obscure differences makes it easier to port code from 2.x to 3.x -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue7117] Backport py3k float repr to trunk
New submission from Mark Dickinson dicki...@gmail.com: See the thread starting at: http://mail.python.org/pipermail/python-dev/2009-October/092958.html Eric suggested that we don't need a separate branch for this; sounds fine to me. It should still be possible to do the backport in stages, though. Something like the following? (1) Check in David Gay's code plus necessary build changes, configuration steps, etc; conversions still use the old code. (2) Switch to using the new code for float - string (str, repr, float formatting) and string - float conversions (float, complex constructors, numeric literals in Python code). [Substeps?] (3) Fix up builtin round function to use the new code. (4) Make any necessary fixes to the documentation. (Raymond, I assume you'll take care of the whatsnew changes when the time comes?) (1), (3) and (4) should be straightforward. (2) is where most of the work is, I think. I think it should be possible to do the stage (2) work in pieces without breaking too much. -- assignee: mark.dickinson components: Interpreter Core messages: 93918 nosy: eric.smith, mark.dickinson, rhettinger priority: normal severity: normal status: open title: Backport py3k float repr to trunk type: feature request versions: Python 2.7 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue7117 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
