Mailman 3 May 2020 - Python-Dev

PEP 617: New PEG parser for CPython
by Guido van Rossum 07 May '20

07 May '20

Since last fall's core sprint in London, Pablo Galindo Salgado, Lysandros Nikolaou and myself have been working on a new parser for CPython. We are now far enough along that we present a PEP we've written: https://www.python.org/dev/peps/pep-0617/ Hopefully the PEP speaks for itself. We are hoping for a speedy resolution so we can land the code we've written before 3.9 beta 1. If people insist I can post a copy of the entire PEP here on the list, but since a lot of it is just background information on the old LL(1) and the new PEG parsing algorithms, I figure I'd spare everyone the need of reading through that. Below is a copy of the most relevant section from the PEP. I'd also like to point out the section on performance (which you can find through the above link) -- basically performance is on a par with that of the old parser. ============== Migration plan ============== This section describes the migration plan when porting to the new PEG-based parser if this PEP is accepted. The migration will be executed in a series of steps that allow initially to fallback to the previous parser if needed: 1. Before Python 3.9 beta 1, include the new PEG-based parser machinery in CPython with a command-line flag and environment variable that allows switching between the new and the old parsers together with explicit APIs that allow invoking the new and the old parsers independently. At this step, all Python APIs like ``ast.parse`` and ``compile`` will use the parser set by the flags or the environment variable and the default parser will be the current parser. 2. After Python 3.9 Beta 1 the default parser will be the new parser. 3. Between Python 3.9 and Python 3.10, the old parser and related code (like the "parser" module) will be kept until a new Python release happens (Python 3.10). In the meanwhile and until the old parser is removed, **no new Python Grammar addition will be added that requires the peg parser**. This means that the grammar will be kept LL(1) until the old parser is removed. 4. In Python 3.10, remove the old parser, the command-line flag, the environment variable and the "parser" module and related code. -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-…>

22 58

A PEP PR that I closed until someone discusses context
by joannah nanjekye 07 May '20

07 May '20

I saw a PR on the PEP repository that looked like a joke here : https://github.com/python/peps/pull/1396 The author can give context to re-open if it was intentional. -- Best, Joannah Nanjekye *"You think you know when you learn, are more sure when you can write, even more when you can teach, but certain when you can program." Alan J. Perlis*

3 2

Maintainer for Multiprocessing
by Philipp Helo Rehs 06 May '20

06 May '20

Hello, it looks like davin is no longer active and there is a pending merge request open more than two years. https://github.com/python/cpython/pull/4819 How can this get merged? Kind regards Philipp Rehs

2 1

Remove ctypes from uuid
by Steve Dower 04 May '20

04 May '20

For those who haven't looked in a while, the uuid module uses ctypes to look up libuuid for uuid_generate_time_safe() and uuid_generate_time() functions. I've run into scenarios where I need to remove this from our own builds, but it seems like it's probably unnecessary anyway? It's certainly a security risk, though in most cases the _uuid module should provide them anyway. I'm proposing to remove the ctypes fallbacks: https://bugs.python.org/issue40501 If anyone knows that they are reliant on not having libuuid at compile time, but being able to load it later via ctypes, it would be great if you could drop by the issue and explain the scenario. Thanks, Steve

2 1

PEP 349 --- deferred but now obsolete?
by Henk-Jaap Wagenaar 04 May '20

04 May '20

The following deferred PEP seems to have become obsolete due to time/Python marching on: PEP 349 - Allow str() to return unicode strings https://www.python.org/dev/peps/pep-0349/ As there is now not non-unicode strings anymore (unless I am misunderstanding the PEP). What should the state of this PEP be updated to? Henk-Jaap

3 3

For-If syntax
by Emily Bowman 04 May '20

04 May '20

I hope this isn't too noobish, nothing on the list comes up in Google, but I'm curious why the construct for x in y if x.is_some_thing: # do a thing isn't legal. That seems a very Pythonic symmetry with lambdas. The equivalent syntax required right now is, for x in [x for x in y if x.is_some_thing]: # do a thing Of course there's more flexibility in the full syntax, but is there any interest in the simpler, more performant one-line syntax? Em

4 4

Moving tzdata into the python organization
by Paul Ganssle 03 May '20

03 May '20

Hi all, PEP 615 specifies that we will add a first party tzdata package <https://www.python.org/dev/peps/pep-0615/#the-tzdata-python-package>. I created this package at pganssle/tzdata <https://github.com/pganssle/tzdata>, but I believe the final home for it should be python/tzdata. Are there any objections to me moving it into the python org as is? Thanks! Paul

2 2

Summary of Python tracker Issues
by Python tracker 01 May '20

01 May '20

ACTIVITY SUMMARY (2020-04-24 - 2020-05-01) 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 7427 (-25) closed 44793 (+118) total 52220 (+93) Open issues with patches: 2954 Issues opened (74) ================== #25597: unittest.mock does not wrap dunder methods (__getitem__ etc) https://bugs.python.org/issue25597 reopened by xtreak #29587: Generator/coroutine 'throw' discards exc_info state, which is https://bugs.python.org/issue29587 reopened by gvanrossum #37340: remove free_list for bound method objects https://bugs.python.org/issue37340 reopened by rhettinger #40246: Different error messages for same error - invalid string prefi https://bugs.python.org/issue40246 reopened by vstinner #40335: [PEP 617 new parser] Regression in multiline SyntaxError offse https://bugs.python.org/issue40335 reopened by Anthony Sottile #40379: multiprocessing's default start method of fork()-without-exec( https://bugs.python.org/issue40379 opened by itamarst #40380: OS-related test failures on Linux in Python 3.8.2 https://bugs.python.org/issue40380 opened by Steven Fleck #40381: plistlib doesn't handle poorly-formatted plists https://bugs.python.org/issue40381 opened by Clay Caviness #40382: Make 'rt' the default for open in docs https://bugs.python.org/issue40382 opened by facundobatista #40383: weakref class name are hardcoded in reprs https://bugs.python.org/issue40383 opened by OhBonsai #40384: IDLE: Wrong highlighting when \n follows def/class https://bugs.python.org/issue40384 opened by Alex-Python-Programmer #40390: Implement _xxsubinterpreters.channel_send_wait(). https://bugs.python.org/issue40390 opened by benedwards14 #40391: io.FileIO.mode doesn't comply with the docs https://bugs.python.org/issue40391 opened by mike.parker #40393: Auto-response from Python Help points to Python 2 reference https://bugs.python.org/issue40393 opened by J Arun Mani #40395: Scripts folder is Empty in python 3.8.2 for Windows 7. https://bugs.python.org/issue40395 opened by BenTen Jan #40397: Refactor typing._GenericAlias https://bugs.python.org/issue40397 opened by serhiy.storchaka #40398: get_args(Callable) fails https://bugs.python.org/issue40398 opened by serhiy.storchaka #40399: IO streams locking can be broken after fork() with threads https://bugs.python.org/issue40399 opened by Delgan #40400: Mac build-installer.py doesn't support new plist format https://bugs.python.org/issue40400 opened by h2a10 #40402: Race condition in multiprocessing/connection.py: broken handle https://bugs.python.org/issue40402 opened by maxicooper #40403: pdb does not drop into debugger upon SyntaxError caused by ast https://bugs.python.org/issue40403 opened by Kerrick Staley #40404: Python quit unexpectedly https://bugs.python.org/issue40404 opened by drliu #40405: asyncio.as_completed documentation misleading https://bugs.python.org/issue40405 opened by bar.harel #40406: MagicMock __aenter__ should be AsyncMock(return_value=MagicMoc https://bugs.python.org/issue40406 opened by graingert #40407: Zipfile couldn`t recognized character set rightly. https://bugs.python.org/issue40407 opened by 김지훈 #40408: GenericAlias does not support nested type variables https://bugs.python.org/issue40408 opened by serhiy.storchaka #40409: urllib.parse.urlsplit parses schemes that do not begin with le https://bugs.python.org/issue40409 opened by sgg #40410: test_multiprocessing_forktest_terminate() timed out after 15 m https://bugs.python.org/issue40410 opened by vstinner #40412: inittab_copy not set to NULL after free, can lead to crashes w https://bugs.python.org/issue40412 opened by indygreg #40413: Py_RunMain() crashes on subsequence call https://bugs.python.org/issue40413 opened by indygreg #40414: Incorrect mouse and keyboard mapping https://bugs.python.org/issue40414 opened by Jah-On #40416: Calling TextIOWrapper.tell() in the middle of reading a gb2312 https://bugs.python.org/issue40416 opened by rmalouf #40417: PyImport_ReloadModule emits deprecation warning https://bugs.python.org/issue40417 opened by Robert Rouhani #40418: Small Refactoring: Use bytes.hex() in secrets.token_hex() https://bugs.python.org/issue40418 opened by Dennis Sweeney #40419: timeit CLI docs still mention old power sequence https://bugs.python.org/issue40419 opened by Energya #40420: argparse choices formatter https://bugs.python.org/issue40420 opened by Leonid Ilyevsky #40421: [C API] Add getter functions for PyFrameObject and maybe move https://bugs.python.org/issue40421 opened by vstinner #40422: Light refactor: create a common _Py_closerange API https://bugs.python.org/issue40422 opened by kevans91 #40423: Optimization: use close_range(2) if available https://bugs.python.org/issue40423 opened by kevans91 #40424: AIX: parallel build and ld WARNINGS https://bugs.python.org/issue40424 opened by Michael.Felt #40425: Refleak in CDataObject https://bugs.python.org/issue40425 opened by cubinator #40426: Unable to use lowercase hexadecimal digits for percent encodin https://bugs.python.org/issue40426 opened by e-kwsm #40429: [C API] PyThreadState_GetFrame() and PyFrame_GetCode() should https://bugs.python.org/issue40429 opened by vstinner #40430: ast.Slice is no longer a subclass of ast.slice https://bugs.python.org/issue40430 opened by Anthony Sottile #40433: Equality operations between lists and arrays https://bugs.python.org/issue40433 opened by Ahmed Amr #40434: Update of reasoning why there is no case statement https://bugs.python.org/issue40434 opened by amaajemyfren #40435: IDLE should catch user config file UnicodeDecodeError https://bugs.python.org/issue40435 opened by 左迟 #40439: Error in an external reference https://bugs.python.org/issue40439 opened by audpa31 #40440: allow array.array construction from memoryview w/o copy https://bugs.python.org/issue40440 opened by bjkeen #40442: Spurious warning emitted during fork() can deadlock a multi-th https://bugs.python.org/issue40442 opened by rojer #40444: multiprocessing.Pool deadlocks with only print statements https://bugs.python.org/issue40444 opened by DarinTay #40445: compileall.compile_dir docs aren't updated for bpo-38112 https://bugs.python.org/issue40445 opened by hauntsaninja #40447: compile_file's stripdir does not accept pathlib.Path https://bugs.python.org/issue40447 opened by hauntsaninja #40448: ensurepip uses cache directory https://bugs.python.org/issue40448 opened by kkonopko #40449: multi-line f-string, syntaxerror points to wrong line https://bugs.python.org/issue40449 opened by Gerrit.Holl #40452: IDLE preserve clipboard on closure (Windows) https://bugs.python.org/issue40452 opened by epaine #40453: Add PyConfig._isolated_interpreter: isolated subinterpreters https://bugs.python.org/issue40453 opened by vstinner #40454: DEBUG kw to asyncio.run overrides DEBUG mode set elsewhere https://bugs.python.org/issue40454 opened by primal #40455: GCC 10 compiler warnings https://bugs.python.org/issue40455 opened by vstinner #40456: Complete adding silent mode for py_compile https://bugs.python.org/issue40456 opened by vstinner #40457: Python fails to compile/load _ssl module if OpenSSL is compile https://bugs.python.org/issue40457 opened by Mitch Lindgren #40458: test_attribute_name_interning crashes on APPX test https://bugs.python.org/issue40458 opened by steve.dower #40459: [easy] undefined names in platform.py https://bugs.python.org/issue40459 opened by vstinner #40460: [easy] undefined name in Lib/idlelib/zzdummy.py https://bugs.python.org/issue40460 opened by vstinner #40461: execution of file with pictures doesn't work in command --onef https://bugs.python.org/issue40461 opened by Hugo Benavides #40462: [easy] undefined name in Lib/test/mock_socket.py https://bugs.python.org/issue40462 opened by vstinner #40463: csv.reader split error https://bugs.python.org/issue40463 opened by wy7305e #40464: functools.singledispatch doesn't verify annotation is on FIRST https://bugs.python.org/issue40464 opened by Dutcho #40465: Deprecate the optional *random* argument to random.shuffle() https://bugs.python.org/issue40465 opened by rhettinger #40466: asyncio.ensure_future() breaks implicit exception chaining https://bugs.python.org/issue40466 opened by chris.jerdonek #40467: subprocess: replacement shell on windows with executable="..." https://bugs.python.org/issue40467 opened by anishathalye #40468: IDLE split "general" into two tabs https://bugs.python.org/issue40468 opened by epaine #40469: TimedRotatingFileHandler rotating on use not time https://bugs.python.org/issue40469 opened by markhallett #40470: Make inspect.signature able to parse format strings. https://bugs.python.org/issue40470 opened by Antony.Lee Most recent 15 issues with no replies (15) ========================================== #40470: Make inspect.signature able to parse format strings. https://bugs.python.org/issue40470 #40469: TimedRotatingFileHandler rotating on use not time https://bugs.python.org/issue40469 #40468: IDLE split "general" into two tabs https://bugs.python.org/issue40468 #40467: subprocess: replacement shell on windows with executable="..." https://bugs.python.org/issue40467 #40466: asyncio.ensure_future() breaks implicit exception chaining https://bugs.python.org/issue40466 #40464: functools.singledispatch doesn't verify annotation is on FIRST https://bugs.python.org/issue40464 #40461: execution of file with pictures doesn't work in command --onef https://bugs.python.org/issue40461 #40459: [easy] undefined names in platform.py https://bugs.python.org/issue40459 #40458: test_attribute_name_interning crashes on APPX test https://bugs.python.org/issue40458 #40456: Complete adding silent mode for py_compile https://bugs.python.org/issue40456 #40454: DEBUG kw to asyncio.run overrides DEBUG mode set elsewhere https://bugs.python.org/issue40454 #40452: IDLE preserve clipboard on closure (Windows) https://bugs.python.org/issue40452 #40449: multi-line f-string, syntaxerror points to wrong line https://bugs.python.org/issue40449 #40448: ensurepip uses cache directory https://bugs.python.org/issue40448 #40445: compileall.compile_dir docs aren't updated for bpo-38112 https://bugs.python.org/issue40445 Most recent 15 issues waiting for review (15) ============================================= #40462: [easy] undefined name in Lib/test/mock_socket.py https://bugs.python.org/issue40462 #40456: Complete adding silent mode for py_compile https://bugs.python.org/issue40456 #40453: Add PyConfig._isolated_interpreter: isolated subinterpreters https://bugs.python.org/issue40453 #40452: IDLE preserve clipboard on closure (Windows) https://bugs.python.org/issue40452 #40448: ensurepip uses cache directory https://bugs.python.org/issue40448 #40445: compileall.compile_dir docs aren't updated for bpo-38112 https://bugs.python.org/issue40445 #40440: allow array.array construction from memoryview w/o copy https://bugs.python.org/issue40440 #40434: Update of reasoning why there is no case statement https://bugs.python.org/issue40434 #40429: [C API] PyThreadState_GetFrame() and PyFrame_GetCode() should https://bugs.python.org/issue40429 #40426: Unable to use lowercase hexadecimal digits for percent encodin https://bugs.python.org/issue40426 #40424: AIX: parallel build and ld WARNINGS https://bugs.python.org/issue40424 #40423: Optimization: use close_range(2) if available https://bugs.python.org/issue40423 #40422: Light refactor: create a common _Py_closerange API https://bugs.python.org/issue40422 #40421: [C API] Add getter functions for PyFrameObject and maybe move https://bugs.python.org/issue40421 #40419: timeit CLI docs still mention old power sequence https://bugs.python.org/issue40419 Top 10 most discussed issues (10) ================================= #40334: PEP 617: new PEG-based parser https://bugs.python.org/issue40334 35 msgs #39995: test_concurrent_futures: ProcessPoolSpawnExecutorDeadlockTest. https://bugs.python.org/issue39995 29 msgs #40246: Different error messages for same error - invalid string prefi https://bugs.python.org/issue40246 19 msgs #29587: Generator/coroutine 'throw' discards exc_info state, which is https://bugs.python.org/issue29587 13 msgs #40360: Deprecate lib2to3 (and 2to3) for future removal https://bugs.python.org/issue40360 13 msgs #40405: asyncio.as_completed documentation misleading https://bugs.python.org/issue40405 11 msgs #40256: Python 3.8 Not Launching on Bootcamp Windows 10. https://bugs.python.org/issue40256 9 msgs #40335: [PEP 617 new parser] Regression in multiline SyntaxError offse https://bugs.python.org/issue40335 9 msgs #40217: The garbage collector doesn't take in account that objects of https://bugs.python.org/issue40217 7 msgs #40399: IO streams locking can be broken after fork() with threads https://bugs.python.org/issue40399 7 msgs Issues closed (106) =================== #8536: Support new features of ZLIB 1.2.7 https://bugs.python.org/issue8536 closed by zach.ware #12503: "with" statement error message is more confusing in Py2.7 https://bugs.python.org/issue12503 closed by zach.ware #13733: Change required to sysconfig.py for Python 2.7.2 on OS/2 https://bugs.python.org/issue13733 closed by zach.ware #14141: 2.7.2 64-bit Windows library has __impt_Py* for several symbol https://bugs.python.org/issue14141 closed by zach.ware #14418: Document differences in SocketServer between Python 2.6 and 2. https://bugs.python.org/issue14418 closed by zach.ware #15408: os.fork/os.popen behaviour change between 2.7 and 3.2 https://bugs.python.org/issue15408 closed by zach.ware #16058: ConfigParser no longer deepcopy compatible in 2.7 https://bugs.python.org/issue16058 closed by zach.ware #16117: python2.7.3 struct misaligned when returned https://bugs.python.org/issue16117 closed by zach.ware #16275: test_ctypes fails on Solaris 10 SPARC 2.7 (nitrogen/s10) (Sun https://bugs.python.org/issue16275 closed by zach.ware #16326: distutils build_ext fails to set library_dirs in 2.7.2 on Linu https://bugs.python.org/issue16326 closed by zach.ware #17126: test_gdb fails https://bugs.python.org/issue17126 closed by zach.ware #17268: Context managers written as C types no longer work in Python 2 https://bugs.python.org/issue17268 closed by zach.ware #17904: bytes should be listed as built-in function for 2.7 https://bugs.python.org/issue17904 closed by zach.ware #18024: dbm module fails to build on SLES11SP1 using 2.7.5 source https://bugs.python.org/issue18024 closed by zach.ware #18493: make profile-opt fails with pre-existing python2.7 in path https://bugs.python.org/issue18493 closed by zach.ware #18567: Python 2.7.5 CENTOS6 Error building dbm using bdb https://bugs.python.org/issue18567 closed by zach.ware #18936: 2.7 distutils getopt chokes on unicode option names https://bugs.python.org/issue18936 closed by zach.ware #19351: python msi installers - silent mode https://bugs.python.org/issue19351 closed by zach.ware #21614: Case sensitivity problem in multiprocessing. https://bugs.python.org/issue21614 closed by zach.ware #21615: Curses bug report for Python 2.7 and Python 3.2 https://bugs.python.org/issue21615 closed by zach.ware #22559: [2.7] Backport ssl.MemoryBIO to Python 2.7 - PEP 546 https://bugs.python.org/issue22559 closed by zach.ware #22583: C stack overflow in the Python 2.7 compiler https://bugs.python.org/issue22583 closed by zach.ware #22863: https://docs.python.org/ should make a true 2.7.8 version avai https://bugs.python.org/issue22863 closed by zach.ware #22912: urlretreive locks up in 2.7.8 https://bugs.python.org/issue22912 closed by zach.ware #23121: pip.exe breaks if python 2.7.9 is installed under c:\Program F https://bugs.python.org/issue23121 closed by zach.ware #23137: Python 2.7.9 test_gdb fails on CentOS 7 https://bugs.python.org/issue23137 closed by zach.ware #24182: test_tcl assertion failure, 2.7, Win 7 https://bugs.python.org/issue24182 closed by zach.ware #24616: 'make install' fails installation of man pages for Python 2.7. https://bugs.python.org/issue24616 closed by zach.ware #25463: 2.7.10 glibc double free detected https://bugs.python.org/issue25463 closed by zach.ware #25560: Unhandled warning in test_unicode_file https://bugs.python.org/issue25560 closed by zach.ware #25563: Windows 10: _tkinter import fails https://bugs.python.org/issue25563 closed by zach.ware #26326: Named entity "vertical line" missed in 2.7 htmlentitydefs.py https://bugs.python.org/issue26326 closed by zach.ware #26360: Deadlock in thread.join on Python 2.7/macOS https://bugs.python.org/issue26360 closed by zach.ware #26652: Cannot install Python 2.7.11 on Windows Server 2008 R2 https://bugs.python.org/issue26652 closed by zach.ware #26665: pip is not bootstrapped by default on 2.7 https://bugs.python.org/issue26665 closed by zach.ware #26697: tkFileDialog crash on askopenfilename Python 2.7 64-bit Win7 https://bugs.python.org/issue26697 closed by zach.ware #26992: 64-bit Python 2.7.11 hangs in 64-bit Windows 10 - CMD and Git https://bugs.python.org/issue26992 closed by zach.ware #27435: ctypes library loading and AIX - also for 2.7.X (and later) https://bugs.python.org/issue27435 closed by zach.ware #27540: msvcrt.ungetwch() calls _ungetch() https://bugs.python.org/issue27540 closed by zach.ware #27562: Import error encodings (Windows xp compatibility) https://bugs.python.org/issue27562 closed by zach.ware #28551: sysconfig.py wrong _PROJECT_BASE for Py2.7 Windows 64bit PC/VS https://bugs.python.org/issue28551 closed by zach.ware #29006: 2.7.13 _sqlite more prone to "database table is locked" https://bugs.python.org/issue29006 closed by zach.ware #29640: _PyThreadState_Init and fork race leads to inconsistent key li https://bugs.python.org/issue29640 closed by zach.ware #29796: [2.7] test_weakref hangs on Python 2.7 on Windows https://bugs.python.org/issue29796 closed by zach.ware #29846: ImportError: Symbol not found: __PyCodecInfo_GetIncrementalDec https://bugs.python.org/issue29846 closed by zach.ware #30725: Windows installer for 2.7.13 doesn't install pip when installi https://bugs.python.org/issue30725 closed by zach.ware #30882: Built-in list disappeared from Python 2.7 intersphinx inventor https://bugs.python.org/issue30882 closed by zach.ware #30967: Crash in PyThread_ReInitTLS() in the child process after os.fo https://bugs.python.org/issue30967 closed by zach.ware #31297: Unpickleable ModuleImportError in unittest patch not backporte https://bugs.python.org/issue31297 closed by zach.ware #31363: __PYVENV_LAUNCHER__ breaks calling another venv's interpreter https://bugs.python.org/issue31363 closed by ned.deily #31474: [2.7] Fix -Wnonnull and -Wint-in-bool-context warnings https://bugs.python.org/issue31474 closed by zach.ware #32049: 2.7.14 does not uninstall cleanly if installation was run as S https://bugs.python.org/issue32049 closed by zach.ware #32494: Use gdbm_count if possible https://bugs.python.org/issue32494 closed by pitrou #33500: Python TKinter for Mac on latest 2.7.15 still extremely slow v https://bugs.python.org/issue33500 closed by zach.ware #33586: 2.7.15 missing release notes on download page https://bugs.python.org/issue33586 closed by zach.ware #33732: Python 2.7.15: xml.sax.parse() closes file objects passed to i https://bugs.python.org/issue33732 closed by zach.ware #34283: [Windows] Python 2 mishandles console code page after setlocal https://bugs.python.org/issue34283 closed by zach.ware #34836: test_ssl.test_default_ecdh_curve needs no tls1.3 flag in 2.7, https://bugs.python.org/issue34836 closed by zach.ware #34884: Python may load incorrect libraries when embedding the macOS s https://bugs.python.org/issue34884 closed by zach.ware #35113: inspect.getsource returns incorrect source for classes when cl https://bugs.python.org/issue35113 closed by xtreak #36803: Getting a lot of runtime misaligned address error while buildi https://bugs.python.org/issue36803 closed by zach.ware #37518: Python-2.7.16 fails to build with --enable-shared https://bugs.python.org/issue37518 closed by zach.ware #38387: Document PyDoc_STRVAR and PyDoc_STR macros https://bugs.python.org/issue38387 closed by zach.ware #38601: Couldn't able to install multiple python minor version in wind https://bugs.python.org/issue38601 closed by zach.ware #38880: Subinterpreters: List interpreters associated with a channel e https://bugs.python.org/issue38880 closed by eric.snow #38959: Parboil -- OpenMP CUTCP performance regression when upgrade fr https://bugs.python.org/issue38959 closed by zach.ware #39072: Azure Pipelines: git clone failed with: OpenSSL SSL_read: Conn https://bugs.python.org/issue39072 closed by vstinner #39482: Write 2to3 fixer for collections.abc imports https://bugs.python.org/issue39482 closed by corona10 #39837: Make Azure Pipelines optional on GitHub PRs https://bugs.python.org/issue39837 closed by brett.cannon #39966: mock 3.9 bug: Wrapped objects without __bool__ raise exception https://bugs.python.org/issue39966 closed by xtreak #40149: test_threading leaked [38, 38, 38] references, sum=114 https://bugs.python.org/issue40149 closed by vstinner #40188: Azure Pipelines jobs failing randomly with: Unable to connect https://bugs.python.org/issue40188 closed by vstinner #40261: Build of Python where make is called from subprocess, within a https://bugs.python.org/issue40261 closed by ned.deily #40269: Inconsistent complex behavior with (-1j) https://bugs.python.org/issue40269 closed by mark.dickinson #40279: Documentation example of module init function lacks error hand https://bugs.python.org/issue40279 closed by scoder #40291: socket library support for CAN_J1939 https://bugs.python.org/issue40291 closed by gvanrossum #40317: inspect.getsource() examines incorrect target https://bugs.python.org/issue40317 closed by xtreak #40338: [Security] urllib and anti-slash (\) in the hostname https://bugs.python.org/issue40338 closed by vstinner #40340: Programming FAQ about "How do I convert a string to a number?" https://bugs.python.org/issue40340 closed by aeros #40346: Add random.BaseRandom to ease implementation of subclasses https://bugs.python.org/issue40346 closed by vstinner #40375: Add the UNSELECT command to imaplib https://bugs.python.org/issue40375 closed by corona10 #40377: APPDATA location in Microsoft Store version https://bugs.python.org/issue40377 closed by stephtr #40378: ast.parse fails to trigger SyntaxWarning that normal execution https://bugs.python.org/issue40378 closed by serhiy.storchaka #40385: Tools/checkpyc.py has been broken since PEP 552 https://bugs.python.org/issue40385 closed by benjamin.peterson #40386: Strange behavior during invalid import of modules without if _ https://bugs.python.org/issue40386 closed by rhettinger #40387: queue example is a sketch https://bugs.python.org/issue40387 closed by rhettinger #40388: random.choice integer overflow v3.5.2 https://bugs.python.org/issue40388 closed by mark.dickinson #40389: No straightforward way to get repr of Optional https://bugs.python.org/issue40389 closed by gvanrossum #40392: Remove deprecated _field_types in typing.NamedTuple https://bugs.python.org/issue40392 closed by xtreak #40394: difflib.SequenceMatcher.find_longest_match default arguments https://bugs.python.org/issue40394 closed by tim.peters #40396: Support GenericAlias in typing https://bugs.python.org/issue40396 closed by serhiy.storchaka #40401: pythoncore.vcxproj fails to load due to duplicated "..\Include https://bugs.python.org/issue40401 closed by zach.ware #40411: frozen collection.Counter https://bugs.python.org/issue40411 closed by rhettinger #40415: _asyncio extensions crashes if initialized multiple times in s https://bugs.python.org/issue40415 closed by indygreg #40427: importlib of module results in different id than when imported https://bugs.python.org/issue40427 closed by brett.cannon #40428: [C API] Remove PyTuple_ClearFreeList() function (move it to th https://bugs.python.org/issue40428 closed by vstinner #40431: turtledemo/__main__.py: SyntaxError: invalid string prefix els https://bugs.python.org/issue40431 closed by vstinner #40432: Pegen regenerate project for Windows not working https://bugs.python.org/issue40432 closed by pablogsal #40436: pythoninfo collect_gdb() blows up when gdb fails to run https://bugs.python.org/issue40436 closed by vstinner #40437: add string.snake function https://bugs.python.org/issue40437 closed by eric.smith #40438: Python 3.9 eval on list comprehension sometimes returns corout https://bugs.python.org/issue40438 closed by vstinner #40441: Plural typo in Design and History FAQ https://bugs.python.org/issue40441 closed by ammar2 #40443: Remove unused imports in the stdlib (April 2020 edition) https://bugs.python.org/issue40443 closed by vstinner #40446: pow(a, b, p) where b=int((p-1)/2) spits out gibbrish for big p https://bugs.python.org/issue40446 closed by ammar2 #40450: a=[1,2,3] a=a.extend([4]) after running these two lines of cod https://bugs.python.org/issue40450 closed by eric.smith #40451: Unexpected sys.getrefcount(foo) output https://bugs.python.org/issue40451 closed by eric.smith

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Adding a "call_once" decorator to functools
by tom＠tomforb.es 01 May '20

01 May '20

Hello, After a great discussion in python-ideas[1][2] it was suggested that I cross-post this proposal to python-dev to gather more comments from those who don't follow python-ideas. The proposal is to add a "call_once" decorator to the functools module that, as the name suggests, calls a wrapped function once, caching the result and returning it with subsequent invocations. The rationale behind this proposal is that: 1. Developers are using "lru_cache" to achieve this right now, which is less efficient than it could be 2. Special casing "lru_cache" to account for zero arity methods isn't trivial and we shouldn't endorse lru_cache as a way of achieving "call_once" semantics 3. Implementing a thread-safe (or even non-thread safe) "call_once" method is non-trivial 4. It complements the lru_cache and cached_property methods currently present in functools. The specifics of the method would be: 1. The wrapped method is guaranteed to only be called once when called for the first time by concurrent threads 2. Only functions with no arguments can be wrapped, otherwise an exception is thrown 3. There is a C implementation to keep speed parity with lru_cache I've included a naive implementation below (that doesn't meet any of the specifics listed above) to illustrate the general idea of the proposal: ``` def call_once(func): sentinel = object() # in case the wrapped method returns None obj = sentinel @functools.wraps(func) def inner(): nonlocal obj, sentinel if obj is sentinel: obj = func() return obj return inner ``` I'd welcome any feedback on this proposal, and if the response is favourable I'd love to attempt to implement it. 1. https://mail.python.org/archives/list/python-ideas@python.org/thread/5OR3LJ… 2. https://discuss.python.org/t/reduce-the-overhead-of-functools-lru-cache-for…

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