Mailman 3 June 2018 - Python-Dev

Idea: reduce GC threshold in development mode (-X dev)
by Victor Stinner June 18, 2018

June 18, 2018

Hi, Yury Selivanov pushed his implementation of the PEP 567 -- Context Variables at January 23, 2018. Yesterday, 4 months after the commit and only 3 weeks before 3.7.0 final release, a crash has been found in the implementation: https://bugs.python.org/issue33803 (it's now fixed, don't worry Ned!) The bug is a "common" mistake in an object constructor implemented in C: the object was tracked by the garbage collector before it was fully initialized, and a GC collection caused a crash somewhere in "object traversing". By "common", I mean that I saw this exact bug between 5 and 10 times over the last 5 years. In the bpo issue, I asked why we only spotted the bug yesterday? It seems like changing the threshold of the GC generation 0 from 700 to 5 triggers the bug immediately in test_context (tests of the PEP 567). I wrote a proof-of-concept patch to change the threshold when using -X dev. Question: Do you think that bugs spotted by a GC collection are common enough to change the GC thresholds in development mode (new -X dev flag of Python 3.7)? GC collections detect various kinds of bugs. Another "common" bug is when an object remains somehow alive in the GC whereas its memory has been freed: using PYTHONMALLOC=debug (debug feature already enabled by -X dev), a GC collection will always crash in such case. I'm not sure about the exact thresholds that would be used in development mode. The general question is more if it would be useful. Then the side question is if reducing the threshold would kill performances or not. About performances, -X dev allows to enable debug features which have an "acceptable" cost in term of performance and memory, but enabled features are chosen on a case by case basis. For example, I chose to *not* enable tracemalloc using -X dev because the cost in term of CPU *and* memory is too high (usually 2x slower and memory x2). Victor

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2018 Python Language Summit coverage, part 2
by Jake Edge June 18, 2018

June 18, 2018

Hola python-dev, Here is some more coverage from the Python Language Summit. As usual, I am posting SubscriberLinks for articles that are still behind the paywall. LWN subscribers can always see our content right away; one week after they are published in a weekly edition, they become freely available for everyone. SubscriberLinks are a way around the paywall. Please feel free to share the SubscriberLinks I am posting here. The starting point is here: https://lwn.net/Articles/754152/ That is an overview article with links to the individual articles. It will be updated as I add more articles. Only 3 more to go after this. Here is what was added since my previous post (which is here: https://lwn.net/ml/python-dev/20180606155653.264c9566%40gallinule/ ) Linux distributions and Python 2 - https://lwn.net/SubscriberLink/756628/7a85f7b28ae3f690/ A Python static typing update - https://lwn.net/SubscriberLink/757218/6f47fe0675cbaf01/ Python virtual environments - https://lwn.net/SubscriberLink/757354/fd82c236dff2de13/ I will post again with the last three, which should be later this week ... enjoy! jake -- Jake Edge - LWN - jake(a)lwn.net - http://lwn.net

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Re: [Python-Dev] PEP 575 (Unifying function/method classes) update
by Jeroen Demeyer June 18, 2018

June 18, 2018

On 2018-06-18 15:09, Victor Stinner wrote: > 2) we implemented a lot of other optimizations which made calls faster > without having to touch tp_call nor tp_fastcall. And that's a problem because these optimizations typically only work for specific classes. My PEP wants to replace those by something more structural.

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the new(-ish) dict ordering vs hash randomization
by Ethan Furman June 18, 2018

June 18, 2018

I'm sure we've already had this conversation, but my google-fu is failing me. Can someone provide a link to a discussion explaining why the new ordering of dictionaries does not defeat the hash-randomization non-ordering we added a few versions ago? -- ~Ethan~

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Re: [Python-Dev] PEP 575 (Unifying function/method classes) update
by Jeroen Demeyer June 18, 2018

June 18, 2018

Hello, I have been working on a slightly different PEP to use a new type slot tp_ccalloffset instead the base_function base class. You can see the work in progress here: https://github.com/jdemeyer/PEP-ccall By creating a new protocol that each class can implement, there is a full decoupling between the features of a class and between the class hierarchy (such coupling was complained about during the PEP 575 discussion). So I got convinced that this is a better approach. It also has the advantage that changes can be made more gradually: this PEP changes nothing at all on the Python side, it only changes the CPython implementation. I still think that it would be a good idea to refactor the class hierarchy, but that's now an independent issue. Another advantage is that it's more general and easier for existing classes to use the protocol (PEP 575 on the other hand requires subclassing from base_function which may not be compatible with an existing class hierarchy). Jeroen.

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Re: [Python-Dev] PEP 575 (Unifying function/method classes) update
by Jeroen Demeyer June 17, 2018

June 17, 2018

On 2018-06-17 14:50, Ronald Oussoren wrote: > This looks interesting. Why did you add a tp_ccalloffset slot to the type with the actual information in instances instead of storing the information in a slot? Think of built-in functions. Every built-in function is a different callable and calls a different C function. So it must be stored in the instances. However, the case where all instances share a PyCCallDef is also possible: all instances would then simply have the same PyCCallDef pointer. Jeroen.

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Some data points for the "annual release cadence" concept
by Nick Coghlan June 17, 2018

June 17, 2018

Hi folks, Given the discussion of adopting an annual release cadence at the language summit this year [1], this recent Jakarta (nee Java) EE announcement caught my attention: https://www.eclipse.org/ee4j/news/?date=2018-06-08#release-cadence JEE are switching to an annual update cadence for the base platform, with quarterly updates for individual components. Since we last seriously discussed potential release cadence changes back in 2012 (with PEPs 407 and 413 [2,3]), that means JEE joins GCC switching to an annual release cadence from GCC 5 back in 2015 (see [4]), while clang/LLVM have been doing twice-annual feature releases for several years now [5]. Most directly relevant to Python would be the Node.js maintenance lifecycle initially developed in 2013, and evolved since then: https://github.com/nodejs/Release That's quite a fast lifecycle (even faster than we're considering - they do a release every 6 months, with every 2nd release being supported for 3 1/2 years), but one of the keys to making it work in practice is https://github.com/nodejs/nan The gist of the "Native Abstractions for Node.js" project is that it aims to provide a stable API & ABI for third party libraries to link against, but *without* having to keep those interfaces stable in V8/Node.js itself. In the Python world, the closest current equivalent would by SIP for PyQt projects [6], which provides a shim layer that allows version independent extension modules to target CPython's native stable ABI with the aid of a single version specific dependency (so only the "sip" wheel itself needs to be rebuilt for each new Python version, not every extension module that depends on it). So I expect a release cadence change would be a lot more viable now than it would have been 6 years ago, but I also suspect actually getting there will require a non-trivial amount of effort invested in generalising the SIP model such that the stable ABI gets a *lot* easier for projects to realistically target (including for cffi and Cython generated extension modules). Cheers, Nick. [1] https://lwn.net/Articles/755224/ [2] https://www.python.org/dev/peps/pep-0407/ [3] https://www.python.org/dev/peps/pep-0413/ [4] https://gcc.gnu.org/releases.html [5] https://releases.llvm.org/ (Note: LLVM switched to twice-yearly X.0.0 releases in 2017, but were doing twice yearly X.Y releases for some time before that) [6] https://pypi.org/project/SIP/ -- Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia

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Re: [Python-Dev] PEP 575 (Unifying function/method classes) update
by Jeroen Demeyer June 17, 2018

June 17, 2018

On 2018-05-19 15:29, Nick Coghlan wrote: > That's not how code reviews work, as their complexity is governed by the > number of lines changed (added/removed/modified), not just the number of > lines that are left at the end. Of course, you are right. I didn't mean literally that only the end result matters. But it should certainly be considered. If you only do small incremental changes, complexity tends to build up because choices which are locally optimal are not always globally optimal. Sometimes you need to do some refactoring to revisit some of that complexity. This is part of what PEP 575 does. > That said, "deletes more lines than it > adds" is typically a point strongly in favour of a particular change. This certainly won't be true for my patch, because there is a lot of code that I need to support for backwards compatibility (all the old code for method_descriptor in particular). Going back to the review of PEP 575, I see the following possible outcomes: (A) Accept it as is (possibly with minor changes). (B) Accept the general idea but split the details up in several PEPs which can still be discussed individually. (C) Accept a minimal variant of PEP 575, only changing existing classes but not changing the class hierarchy. (D) Accept some yet-to-be-written variant of PEP 575. (E) Don't fix the use case that PEP 575 wants to address. Petr Viktorin suggests (C). I am personally quite hesitant because that only adds complexity and it wouldn't be the best choice for the future maintainability of CPython. I also fear that this hypothetical PEP variant would be rejected because of that reason. Of course, if there is some general agreement that (C) is the way to go, then that is fine for me. If people feel that PEP 575 is currently too complex, I think that (B) is a very good compromise. The end result would be the same as what PEP 575 proposes. Instead of changing many things at once, we could handle each class in a separate PEP. But the motivation of those mini-PEPs will still be PEP 575. So, in order for this to make sense, the general idea of PEP 575 needs to be accepted: adding a base_function base class and making various existing classes subclasses of that. Jeroen.

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Summary of Python tracker Issues
by Python tracker June 15, 2018

June 15, 2018

ACTIVITY SUMMARY (2018-06-08 - 2018-06-15) Python tracker at https://bugs.python.org/ To view or respond to any of the issues listed below, click on the issue. Do NOT respond to this message. Issues counts and deltas: open 6691 ( -1) closed 38930 (+62) total 45621 (+61) Open issues with patches: 2644 Issues opened (42) ================== #33656: IDLE: Turn on DPI awareness on Windows https://bugs.python.org/issue33656 reopened by terry.reedy #33811: asyncio accepting connection limit https://bugs.python.org/issue33811 opened by lguo #33813: Update overdue 'Deprecated ... removed in 3.x' messages https://bugs.python.org/issue33813 opened by terry.reedy #33816: New metaclass example for Data Model topic https://bugs.python.org/issue33816 opened by adelfino #33817: PyString_FromFormatV() fails to build empty strings https://bugs.python.org/issue33817 opened by Tey #33820: IDLE subsection of What's New 3.6 https://bugs.python.org/issue33820 opened by terry.reedy #33821: IDLE subsection of What's New 3.7 https://bugs.python.org/issue33821 opened by terry.reedy #33822: IDLE subsection of What's New 3.8 https://bugs.python.org/issue33822 opened by terry.reedy #33823: A BUG in concurrent/asyncio https://bugs.python.org/issue33823 opened by Python++ #33824: Settign LANG=C modifies the --version behavior https://bugs.python.org/issue33824 opened by hroncok #33826: enable discovery of class source code in IPython interactively https://bugs.python.org/issue33826 opened by t-vi #33829: C API: provide new object protocol helper https://bugs.python.org/issue33829 opened by Bartosz Gołaszewski #33830: Error in the output of one example in the httplib docs https://bugs.python.org/issue33830 opened by Aifu LIU #33832: Make "magic methods" a little more discoverable in the docs https://bugs.python.org/issue33832 opened by adelfino #33833: ProactorEventLoop raises AssertionError https://bugs.python.org/issue33833 opened by twisteroid ambassador #33834: Test for ProactorEventLoop logs InvalidStateError https://bugs.python.org/issue33834 opened by twisteroid ambassador #33836: [Good first-time issue] Recommend keyword-only param for memoi https://bugs.python.org/issue33836 opened by zach.ware #33837: Closing asyncio.Server on asyncio.ProactorEventLoop causes all https://bugs.python.org/issue33837 opened by mliska #33838: Very slow upload with http.client on Windows when setting time https://bugs.python.org/issue33838 opened by ivknv #33839: IDLE tooltips.py: refactor and add docstrings and tests https://bugs.python.org/issue33839 opened by terry.reedy #33840: connection limit on listening socket in asyncio https://bugs.python.org/issue33840 opened by lguo #33841: lock not released in threading.Condition https://bugs.python.org/issue33841 opened by lev.maximov #33842: Remove tarfile.filemode https://bugs.python.org/issue33842 opened by inada.naoki #33843: Remove deprecated stuff in cgi module https://bugs.python.org/issue33843 opened by inada.naoki #33846: Misleading error message in urllib.parse.unquote https://bugs.python.org/issue33846 opened by thet #33847: doc: Add '@' operator entry to index https://bugs.python.org/issue33847 opened by adelfino #33851: 3.7 regression: ast.get_docstring() for a node that lacks a do https://bugs.python.org/issue33851 opened by mgedmin #33852: doc Remove parentheses from sequence subscription description https://bugs.python.org/issue33852 opened by adelfino #33854: doc Add PEP title in seealso of Built-in Types https://bugs.python.org/issue33854 opened by adelfino #33855: IDLE: Minimally test every non-startup module. https://bugs.python.org/issue33855 opened by terry.reedy #33856: Type "help" is not present on win32 https://bugs.python.org/issue33856 opened by matrixise #33857: python exception on Solaris : code for hash blake2b was not fo https://bugs.python.org/issue33857 opened by goron #33858: A typo in multiprocessing documentation https://bugs.python.org/issue33858 opened by aruseni #33859: Spelling mistakes found using aspell https://bugs.python.org/issue33859 opened by xtreak #33861: Minor improvements of tests for os.path. https://bugs.python.org/issue33861 opened by serhiy.storchaka #33864: collections.abc.ByteString does not register memoryview https://bugs.python.org/issue33864 opened by fried #33865: [EASY] Missing code page aliases: "unknown encoding: 874" https://bugs.python.org/issue33865 opened by winvinc #33866: Stop using OrderedDict in enum https://bugs.python.org/issue33866 opened by inada.naoki #33867: Module dicts are wiped on module garbage collection https://bugs.python.org/issue33867 opened by natedogith1 #33868: test__xxsubinterpreters: test_subinterpreter() fails randomly https://bugs.python.org/issue33868 opened by vstinner #33869: doc Add set, frozen set, and tuple entries to Glossary https://bugs.python.org/issue33869 opened by adelfino #33870: pdb continue + breakpoint https://bugs.python.org/issue33870 opened by philiprowlands Most recent 15 issues with no replies (15) ========================================== #33870: pdb continue + breakpoint https://bugs.python.org/issue33870 #33869: doc Add set, frozen set, and tuple entries to Glossary https://bugs.python.org/issue33869 #33867: Module dicts are wiped on module garbage collection https://bugs.python.org/issue33867 #33866: Stop using OrderedDict in enum https://bugs.python.org/issue33866 #33861: Minor improvements of tests for os.path. https://bugs.python.org/issue33861 #33859: Spelling mistakes found using aspell https://bugs.python.org/issue33859 #33857: python exception on Solaris : code for hash blake2b was not fo https://bugs.python.org/issue33857 #33856: Type "help" is not present on win32 https://bugs.python.org/issue33856 #33854: doc Add PEP title in seealso of Built-in Types https://bugs.python.org/issue33854 #33847: doc: Add '@' operator entry to index https://bugs.python.org/issue33847 #33843: Remove deprecated stuff in cgi module https://bugs.python.org/issue33843 #33842: Remove tarfile.filemode https://bugs.python.org/issue33842 #33841: lock not released in threading.Condition https://bugs.python.org/issue33841 #33838: Very slow upload with http.client on Windows when setting time https://bugs.python.org/issue33838 #33834: Test for ProactorEventLoop logs InvalidStateError https://bugs.python.org/issue33834 Most recent 15 issues waiting for review (15) ============================================= #33869: doc Add set, frozen set, and tuple entries to Glossary https://bugs.python.org/issue33869 #33866: Stop using OrderedDict in enum https://bugs.python.org/issue33866 #33865: [EASY] Missing code page aliases: "unknown encoding: 874" https://bugs.python.org/issue33865 #33859: Spelling mistakes found using aspell https://bugs.python.org/issue33859 #33855: IDLE: Minimally test every non-startup module. https://bugs.python.org/issue33855 #33854: doc Add PEP title in seealso of Built-in Types https://bugs.python.org/issue33854 #33851: 3.7 regression: ast.get_docstring() for a node that lacks a do https://bugs.python.org/issue33851 #33847: doc: Add '@' operator entry to index https://bugs.python.org/issue33847 #33843: Remove deprecated stuff in cgi module https://bugs.python.org/issue33843 #33842: Remove tarfile.filemode https://bugs.python.org/issue33842 #33839: IDLE tooltips.py: refactor and add docstrings and tests https://bugs.python.org/issue33839 #33836: [Good first-time issue] Recommend keyword-only param for memoi https://bugs.python.org/issue33836 #33833: ProactorEventLoop raises AssertionError https://bugs.python.org/issue33833 #33832: Make "magic methods" a little more discoverable in the docs https://bugs.python.org/issue33832 #33829: C API: provide new object protocol helper https://bugs.python.org/issue33829 Top 10 most discussed issues (10) ================================= #33656: IDLE: Turn on DPI awareness on Windows https://bugs.python.org/issue33656 26 msgs #33630: test_posix: TestPosixSpawn fails on PPC64 Fedora 3.x https://bugs.python.org/issue33630 22 msgs #1529353: Squeezer - squeeze large output in the interpreter https://bugs.python.org/issue1529353 14 msgs #14102: argparse: add ability to create a man page https://bugs.python.org/issue14102 12 msgs #33462: reversible dict https://bugs.python.org/issue33462 10 msgs #33738: PyIndex_Check conflicts with PEP 384 https://bugs.python.org/issue33738 9 msgs #29750: smtplib doesn't handle unicode passwords https://bugs.python.org/issue29750 7 msgs #33865: [EASY] Missing code page aliases: "unknown encoding: 874" https://bugs.python.org/issue33865 7 msgs #27777: cgi.FieldStorage can't parse simple body with Content-Length a https://bugs.python.org/issue27777 6 msgs #32962: test_gdb fails in debug build with `-mcet -fcf-protection -O0` https://bugs.python.org/issue32962 6 msgs Issues closed (56) ================== #11874: argparse assertion failure with brackets in metavars https://bugs.python.org/issue11874 closed by ncoghlan #17045: Improve C-API doc for PyTypeObject https://bugs.python.org/issue17045 closed by eric.snow #17286: Make subprocess handling text output with universal_newlines m https://bugs.python.org/issue17286 closed by cheryl.sabella #19382: tabnanny unit tests https://bugs.python.org/issue19382 closed by vstinner #22264: Add wsgiref.util.dump_wsgistr & load_wsgistr https://bugs.python.org/issue22264 closed by ncoghlan #22555: Tracking issue for adjustments to binary/text boundary handlin https://bugs.python.org/issue22555 closed by ncoghlan #23869: Initialization is being done in PyType_GenericAlloc https://bugs.python.org/issue23869 closed by eric.snow #24384: difflib.SequenceMatcher faster quick_ratio with lower bound sp https://bugs.python.org/issue24384 closed by floyd #26698: Tk DPI awareness https://bugs.python.org/issue26698 closed by terry.reedy #27397: email.message.Message.get_payload(decode=True) raises Assertio https://bugs.python.org/issue27397 closed by taleinat #29456: bugs in unicodedata.normalize: u1176, u11a7 and u11c3 https://bugs.python.org/issue29456 closed by xiang.zhang #30805: asyncio: race condition with debug and subprocess https://bugs.python.org/issue30805 closed by yselivanov #30820: email.contentmanager.raw_data_manager fails to create multipar https://bugs.python.org/issue30820 closed by r.david.murray #31102: deheader: double #incude of the same file https://bugs.python.org/issue31102 closed by Mariatta #31120: [2.7] Python 64 bit _ssl compile fails due missing buildinf_am https://bugs.python.org/issue31120 closed by zach.ware #31181: Segfault in gcmodule.c:360 visit_decref (PyObject_IS_GC(op)) https://bugs.python.org/issue31181 closed by vstinner #31215: Add version changed notes for OpenSSL 1.1.0 compatibility https://bugs.python.org/issue31215 closed by ncoghlan #31378: Missing documentation for sqlite3.OperationalError https://bugs.python.org/issue31378 closed by berker.peksag #32400: inspect.isdatadescriptor false negative https://bugs.python.org/issue32400 closed by berker.peksag #33375: warnings: get filename from frame.f_code.co_filename https://bugs.python.org/issue33375 closed by brett.cannon #33409: Clarify the interaction between locale coercion & UTF-8 mode https://bugs.python.org/issue33409 closed by ncoghlan #33582: formatargspec deprecated but does not emit DeprecationWarning. https://bugs.python.org/issue33582 closed by ned.deily #33642: IDLE: Display up to maxlines non-blank lines for Code Context https://bugs.python.org/issue33642 closed by terry.reedy #33671: Efficient zero-copy for shutil.copy* functions (Linux, OSX and https://bugs.python.org/issue33671 closed by giampaolo.rodola #33694: test_asyncio: test_start_tls_server_1() fails on Python on x86 https://bugs.python.org/issue33694 closed by vstinner #33741: UnicodeEncodeError onsmtplib.login(MAIL_USER, MAIL_PASSWORD) https://bugs.python.org/issue33741 closed by r.david.murray #33745: 3.7.0b5 changes the line number of empty functions with docstr https://bugs.python.org/issue33745 closed by ned.deily #33748: test_discovery_failed_discovery in test_unittest modifies sys. https://bugs.python.org/issue33748 closed by ned.deily #33751: Failed separate testTruncateOnWindows in test_file https://bugs.python.org/issue33751 closed by serhiy.storchaka #33766: Grammar Incongruence https://bugs.python.org/issue33766 closed by terry.reedy #33770: base64 throws 'incorrect padding' exception when the issue is https://bugs.python.org/issue33770 closed by ned.deily #33771: Module: timeit. According to documentation default_repeat shou https://bugs.python.org/issue33771 closed by terry.reedy #33799: Remove non-ordered dicts comments from FAQ https://bugs.python.org/issue33799 closed by adelfino #33800: Fix default argument for parameter dict_type of ConfigParser/R https://bugs.python.org/issue33800 closed by ned.deily #33801: Remove non-ordered dict comment from plistlib https://bugs.python.org/issue33801 closed by ned.deily #33802: Regression in logging configuration https://bugs.python.org/issue33802 closed by barry #33810: Remove unused code in datetime module https://bugs.python.org/issue33810 closed by belopolsky #33812: Different behavior between datetime.py and its C accelerator https://bugs.python.org/issue33812 closed by belopolsky #33814: exec() maybe has a memory leak https://bugs.python.org/issue33814 closed by tim.peters #33815: List a = []*19 doesn't create a list with index length of 19 https://bugs.python.org/issue33815 closed by zach.ware #33818: Make PyExceptionClass_Name returning a const string https://bugs.python.org/issue33818 closed by serhiy.storchaka #33819: Mention "ordered mapping" instead of "ordered dictionary" in e https://bugs.python.org/issue33819 closed by r.david.murray #33825: Change mentions of "magic" attributes to "special" https://bugs.python.org/issue33825 closed by adelfino #33827: Generators with lru_cache can be non-intuituve https://bugs.python.org/issue33827 closed by rhettinger #33828: Add versionchanged notes for string.Formatter https://bugs.python.org/issue33828 closed by xiang.zhang #33831: Make htmlview work in make.bat https://bugs.python.org/issue33831 closed by adelfino #33835: Too strong side effect? https://bugs.python.org/issue33835 closed by serhiy.storchaka #33844: Writing capital letters with csvwriter.writerow changes the cs https://bugs.python.org/issue33844 closed by serhiy.storchaka #33845: Update Doc\make.bat on 2.7 to bring it on par to master versio https://bugs.python.org/issue33845 closed by steve.dower #33848: Incomplete format string syntax for Exceptions https://bugs.python.org/issue33848 closed by eric.smith #33849: Caught infinite recursion resets the trace function https://bugs.python.org/issue33849 closed by belopolsky #33850: Json.dump() bug when using generator https://bugs.python.org/issue33850 closed by eric.smith #33853: test_multiprocessing_spawn is leaking memory https://bugs.python.org/issue33853 closed by serhiy.storchaka #33860: doc Avoid "ordered dictionary" references now that dictionarie https://bugs.python.org/issue33860 closed by ethan.furman #33862: doc Fix Enum __members__ type https://bugs.python.org/issue33862 closed by ethan.furman #33863: Enum doc correction relating to __members__ https://bugs.python.org/issue33863 closed by ethan.furman

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A more flexible task creation
by Michel Desmoulin June 15, 2018

June 15, 2018

I was working on a concurrency limiting code for asyncio, so the user may submit as many tasks as one wants, but only a max number of tasks will be submitted to the event loop at the same time. However, I wanted that passing an awaitable would always return a task, no matter if the task was currently scheduled or not. The goal is that you could add done callbacks to it, decide to force schedule it, etc I dug in the asyncio.Task code, and encountered: def __init__(self, coro, *, loop=None): ... self._loop.call_soon(self._step) self.__class__._all_tasks.add(self) I was surprised to see that instantiating a Task class has any side effect at all, let alone 2, and one of them being to be immediately scheduled for execution. I couldn't find a clean way to do what I wanted: either you loop.create_task() and you get a task but it runs, or you don't run anything, but you don't get a nice task object to hold on to. I tried several alternatives, like returning a future, and binding the future awaiting to the submission of a task, but that was complicated code that duplicated a lot of things. I tried creating a custom task, but it was even harder, setting a custom event policy, to provide a custom event loop with my own create_task() accepting parameters. That's a lot to do just to provide a parameter to Task, especially if you already use a custom event loop (e.g: uvloop). I was expecting to have to create a task factory only, but task factories can't get any additional parameters from create_task()). Additionally I can't use ensure_future(), as it doesn't allow to pass any parameter to the underlying Task, so if I want to accept any awaitable in my signature, I need to provide my own custom ensure_future(). All those implementations access a lot of _private_api, and do other shady things that linters hate; plus they are fragile at best. What's more, Task being rewritten in C prevents things like setting self._coro, so we can only inherit from the pure Python slow version. In the end, I can't even await the lazy task, because it blocks the entire program. Hence I have 2 distinct, but independent albeit related, proposals: - Allow Task to be created but not scheduled for execution, and add a parameter to ensure_future() and create_task() to control this. Awaiting such a task would just do like asyncio.sleep(O) until it is scheduled for execution. - Add an parameter to ensure_future() and create_task() named "kwargs" that accept a mapping and will be passed as **kwargs to the underlying created Task. I insist on the fact that the 2 proposals are independent, so please don't reject both if you don't like one or the other. Passing a parameter to the underlying custom Task is still of value even without the unscheduled instantiation, and vice versa. Also, if somebody has any idea on how to make a LazyTask that we can await on without blocking everything, I'll take it.

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