Mailman 3 June 2017 - Python-Dev

(no subject)
by Victor Stinner June 30, 2017

June 30, 2017

Hi Robb, 2017-06-29 23:34 GMT+02:00 Rob Boehne <robb(a)datalogics.com>: > I¹m new to the list, and contributing to Python specifically, and I¹m > interested in getting master and 3.6 branches building and working > ³better² on UNIX. > I¹ve been looking at a problem building 3.6 on HP-UX and see a PR was > merged into master, https://github.com/python/cpython/pull/1351 and I¹d > like to see it applied to 3.6. I¹m happy to create a PR with a > cherry-picked commit, and/or test. Sure, this change can be backported to 3.6, maybe also to 3.5. But hum, I may suggest to first focus on the master branch and fix most HP-UX issues, before spending time on backport. I would prefer to see most tests of the important modules pass on HP-UX (ex: test_os). For a backport, you can directly comment http://bugs.python.org/issue30183 Victor

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Bug in buildbot view (changes column)
by Antoine Pitrou June 30, 2017

June 30, 2017

Hello, If you look at this page (waterfall view of 3.x unstable buildbots), you'll notice the "changes" column on the left lists the recent changesets on master: http://buildbot.python.org/all/waterfall?tag=3.x.unstable However, on the equivalent view for 3.x stable buildbots, the "changes" column on the left is empty: http://buildbot.python.org/all/waterfall?category=3.x.stable Is there a particular reason? Oh wait... The first URL lists "3.x.unstable" as a *tag* while the second URL lists "3.x.stable" as a *category*. If I change the second URL to use "tag" instead of "category", the "changes" column miraculously lists the recent changesets: http://buildbot.python.org/all/waterfall?tag=3.x.stable Finicky buildbot :-/ Regards Antoine.

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Micro-optimizations by adding special-case bytecodes?
by Ben Hoyt June 28, 2017

June 28, 2017

Hi folks, I was looking at some `dis` output today, and I was wondering if anyone has investigated optimizing Python (slightly) by adding special-case bytecodes for common expressions or statements involving constants? For example, I (and, based on a quick grep of the stdlib, many others) write "x is None" and "x is not None" very often. Or "return True" or "return None" or "return 1" and things like that. These all expand into two bytecodes, which seems pretty non-optimal (LOAD_CONST + COMPARE_OP or LOAD_CONST + RETURN_VALUE). It seems we could get an easy speedup for these common cases by adding a peephole optimization and some new opcodes (maybe COMPARE_IS_SMALL_CONST and RETURN_SMALL_CONST for these cases). I'm not proposing to do this yet, as I'd need to benchmark to see how much of a gain (if any) it would amount to, but I'm just wondering if there's any previous work on this kind of thing. Or, if not, any other thoughts before I try it? Thanks, Ben

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Proposal for C++ metaclasses
by Steve Dower June 27, 2017

June 27, 2017

Thought this might be interesting for those of us who live deeper in the language than most – this is the formal proposal to add metaclasses to C++. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0707r0.pdf Given the differences between Python and C++, it’s obviously got a different approach, though I am struck by the similarities. I think it’s also a good presentation on the value and use of metaclasses, so likely also interesting for those of us who occasionally teach or explain the concept. Cheers, Steve

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New workflow change: Welcome to blurb
by Larry Hastings June 27, 2017

June 27, 2017

One minor but ongoing problem we've had in CPython core development has been the mess of updating Misc/NEWS. Day-to-day developers may have a conflict if they lose a push race, which means a little editing. You'll have a similar, if slightly worse, problem when cherry-picking a fix between versions. Worst of all used to be the manual merges necessary after cutting a release--this was the bane of a CPython release manager's existence. (Though the new git-based workflow may have obviated the worst of this.) The real problem is that we have one central file that everybody continually edits in a haphazard way. We aren't actually editing the same information, we aren't actually changing the same lines. But our revision control systems and diff algorithms don't understand the structure of Misc/NEWS and so they get confused. And for what? It's not like there's a tremendous benefit to having this central file everyone's fighting over. We've been talking about addressing this for years. Fixing this was one of the goals of the new workflow. And finally, as of right now, the future is here. Ladies and gentlemen, I present: blurb. https://github.com/python/core-workflow/tree/master/blurb blurb is an interactive command-line tool that helps you write Misc/NEWS entries. You simply run blurb from anywhere inside a CPython repo. blurb runs an editor for you with a template open. You fill in these three pieces of information: * the bugs.python.org or "bpo" issue number, * what "section" of Misc/NEWS this entry should go in (by uncommenting the correct line), and * the text of the Misc/NEWS entry, in ReST format. You save and exit and you're done. blurb even stages the Misc/NEWS entry in git for you! Behind the scenes, blurb writes your information here: Misc/NEWS.d/next/<section-name>/<filename> The "<section-name>" is the name of the section in Misc/NEWS where your entry should go. <filename> contains the current date and time, the bpo number, and a nonce to prevent collisions. These "next" files get merged together into a single aggregate .rst file by the release manager when cutting a release (using "blurb release"). One nice feature of this approach: when you cherry-pick a change, its Misc/NEWS entry in "next" gets cherry-picked along with it. One important change: Misc/NEWS will no longer be checked in. It'll still be present in CPython tarballs; it will be generated by the release manager as part of cutting a release. But as a repository of information, it's been superseded by the various blurb data files. And by regenerating it from data files, we ensure that we'll never ever have a Misc/NEWS conflict ever again! The plan is to leave Misc/NEWS in the CPython repo for maybe another week, to let the current crop of PRs get merged. But new work should switch to using blurb immediately. You can install blurb from pip: % pip3.6 install blurb In fact--please do! //arry/

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PEP 538 warning at startup: please remove it
by Victor Stinner June 26, 2017

June 26, 2017

Hi, Nick Coghlan pushed his implementation of his PEP 538: nice! Nice step forward to UTF-8 everywhere ;-) I would prefer to not be annoyed by warning messages about encodings at startup if possible: "Python detected LC_CTYPE=C: LC_CTYPE coerced to C.UTF-8 (set another locale or PYTHONCOERCECLOCALE=0 to disable this locale coercion behavior)." Python 3.7 is the only programming language that I know that complains about encoding at startup. Even if my code is 100% valid, PEP 8 compliant, don't emit any warning, etc. I will get the warning. It is *not* possible to ignore the warning... Like "yeah, I know that my locale is C, but it's not like I'm able to configure it." haypo@selma$ export LANG= haypo@selma$ locale LANG= LC_CTYPE="POSIX" ... haypo@selma$ ./python -c 'print("Hello World!")' # Python 3.7 Python detected LC_CTYPE=C: LC_CTYPE coerced to C.UTF-8 (set another locale or PYTHONCOERCECLOCALE=0 to disable this locale coercion behavior). Hello World! haypo@selma$ python2 -c 'print("Hello World!")' # Python 2.7 Hello World! haypo@selma$ perl -e 'print "Hello, world!\n"' # Perl 5.24 Hello, world! haypo@selma$ ./c # C Hello World! ... Note: I don't consider that 2>/dev/null is a good practice to ignore a single warning, since it will ignore *all* message written into stderr, including useful warnings like ResourceWarning or "Exception ignored ...". Victor

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__qualname__ format question
by Christian Tismer June 25, 2017

June 25, 2017

Hi friends, by chance, I stumbled over meth_get__qualname__ in methodobject.c and calculate_qualname in descrobject.c . The first uses res = PyUnicode_FromFormat("%S.%s", type_qualname, m->m_ml->ml_name); and the latter uses res = PyUnicode_FromFormat("%S.%S", type_qualname, descr->d_name); To my knowledge, the "%S" character is undefined in C99 and C11. Q: Why this character, and why this difference? cheers - Chris -- Christian Tismer :^) tismer(a)stackless.com Software Consulting : http://www.stackless.com/ Karl-Liebknecht-Str. 121 : https://github.com/PySide 14482 Potsdam : GPG key -> 0xFB7BEE0E phone +49 173 24 18 776 fax +49 (30) 700143-0023

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Appveyor builds fail on Windows for 3.6 backports.
by Terry Reedy June 24, 2017

June 24, 2017

Example: appveyor passes for https://github.com/python/cpython/pull/2335#discussion_r123724857 Appveyor build fails for 3.6 backport https://github.com/python/cpython/pull/2359 https://ci.appveyor.com/project/python/cpython/build/3.6.1+.3673 The compile and build errors have nothing to do with the patch. This failure is routine; turning off appveyor for 3.6, until fixed, would reduce noise. I presume this is a workflow issue, but I don't know if Windows experts would see it. -- Terry Jan Reedy

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Re: [Python-Dev] [Core-mentorship] C version of weakrefset.py.
by Bhavishya June 23, 2017

June 23, 2017

Hello, 1)I might be totally wrong here, but even if we go with stripping annotation(in .pyc)...still the "lag" that comes from ABCs needs to be addressed. 2) I been reading for past few days about your fat-optimizer project and the corresponding TO-DO list, if you think that PEP-0511 should be improved, I can work on that. 3)Also I was seeing to existing repos which implement some-kind of optimizaton, like numpy,snake-oil.... Finally I wanted to decide upon a roadmap, so that I could put more specific efforts.(fat optimizer?) Thank You Regards, Bhavishya On Wed, Jun 21, 2017 at 8:05 PM, Victor Stinner <victor.stinner(a)gmail.com> wrote: > 2017-06-21 15:21 GMT+02:00 INADA Naoki <songofacandy(a)gmail.com>: > > ABC slowdown Python startup only 2ms. But importing typing module take > 11ms. > > While typing is not imported from site.py, many new Python application > > will import it. > > It may take over 100ms for applications or libraries heavily depending > on ABCs. > > When typing is not used in the application, only used for static > checks, you can try to "strip" annotations to avoid any overhead on > the application startup. It's not only a matter of "import typing", > it's also the cost of instanciating types like "List[int]" (or even > more complex ones). > > I discussed with Jukka Lehtosalo at Pycon US about stripping > completely annotations. He told me that my PEP 511 may be a good > solution to keep annotation in the .py code, but strip them for > "production code", in the cached .pyc files: > > "PEP 511 -- API for code transformers" > https://www.python.org/dev/peps/pep-0511/ > > This PEP is somehow controversal. Some people fear that it would allow > people to hack the Python language to write their own incompatible > variant of Python. I don't think that my PEP adds anything new, it's > already possible to do that, importlib made it even more easy. I used > my FAT Python optimizer project to sell this PEP. Since FAT Python is > also controversal (it hasn't been proved to be actually faster), the > PEP didn't go far at my last attempt. > > Note: Is core-menthorship the best place for such performance > discussion? :-) Maybe we should open a thread on python-dev@ or speed@ > mailing list. > > Victor >

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Proposed release schedule for Python 3.5.4
by Larry Hastings June 23, 2017

June 23, 2017

It's time to start planning the next 3.5 release, 3.5.4. Note that this will be the last 3.5 "bugfix" release; after 3.5.4, the 3.5 branch will only be open for security fixes. 3.5.4 will also be the last release of 3.5 with binary installers. I propose to tag and release 3.5.4 on these dates: 3.5.4rc1 tag Sat July 22 2017 release Sun July 23 2017 3.5.4 final tag Sun Aug 6 2017 release Mon Aug 7 2017 Thus rc1 would be tagged in just over four weeks. As for 3.4-- Lately I've been releasing new versions of 3.5 and 3.4 at the same time. But I'm not sure it's worth the effort to release another 3.4 right now. There have only been two (2) checkins into the 3.4 branch since 3.4.6 was released back in January: f37b0cb230069481609b0bb06891b5dd26320504 bpo-25008: Deprecate smtpd and point to aiosmtpd fa53dbdec818b0f2a0e22ca12a49d83ec948fc91 Issues #27850 and #27766: Remove 3DES from ssl default cipher list and add ChaCha20 Poly1305. The first was a documentation-only change which is already live on docs.python.org. The second changes the _DEFAULT_CIPHERS and _RESTRICTED_SERVER_CIPHERS constants in Lib/ssl.py. A reasonable change, but minor. I'm not convinced it's worth spending the time of many people in the community at large to update 3.4 just for this. If you have any feedback / concerns about this schedule, or if you think it's important that I release 3.4.7 with these minor changes, please reply here. If I don't hear anything back in a day or two I'll go ahead and make this the official schedule. Your friendly neighborhood release manager, //arry/

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