Mailman 3 November 2020 - Python-Dev

review for doctest fix: bpo-35753
by Alfred Perlstein Nov. 25, 2020

Nov. 25, 2020

Hello, We are using doctest to give our developers easy access to write very fast unit tests and encourage "tests as documentation". Recently we hit an issue where doctest crashes on certain objects that fail to "unwrap". Looking at the code and reasoning behind the crash it seems like we can simply ignore a failed call to unwraps. There is now a PR open against against trunk and 3.8 branch (happy to make a 3.9 branch PR as well) here: trunk: https://github.com/python/cpython/pull/22981 3.8: https://github.com/python/cpython/pull/22834 Does anyone have time to review and/or comment on this? Thank you, -Alfred

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A question about pattern matching
by Marco Sulla Nov. 24, 2020

Nov. 24, 2020

Excuse me, I have a question about pattern matching: is it used often in math language as Mathematica? May it help to translate code from such languages to Python?

2 1

Remove formatter module
by Dong-hee Na Nov. 24, 2020

Nov. 24, 2020

A few days ago, Terry J. Reedy created the issue about the formatter module. (https://bugs.python.org/issue42299) The issue is mainly about testing code but also discussing the removal of the module. I noticed that the formatter module was deprecated in 3.4 and it was originally scheduled to be removed in 3.6. But the removal was delayed until 2.7 EOL. Now 2.7 is EOL and there is no usage in stdlib. So IMHO, it is good to remove the formatter module in 3.10 So before removing it, I would like to hear the concern. Regards, Dong-hee

5 5

Words rather than sigils in Structural Pattern Matching
by David Mertz Nov. 23, 2020

Nov. 23, 2020

I have read a great deal of discussion on the pattern matching PEPs and less formal discussions. It is possible I have overlooked some post in all of that, of course. ... OK, just saw Guido's "wait for new SC" comment, which I suppose applies to this too :-). One idea that I cannot recall seeing, but that seems to make sense to me and fit with Python's feel is using a WORD to distinguish between a variable value and a binding target. That is, instead of a special symbol prefixing or suffixing a name, either to indicate it is or is not a binding target. Of course, whether the extra word would be used for binding or for NOT binding is a question still. NOT_FOUND = 404 match http_code: case 200: print("OK document") case value NOT_FOUND: # use the variable value print("Document not found") case OTHER_CODE: # bind this name print("Other HTTP code", OTHER_CODE) Of course, this would require a soft keyword, which is a disadvantage. Going the other direction: NOT_FOUND = 404 match http_code: case 200: print("OK document") case NOT_FOUND: # use the variable value print("Document not found") case bind OTHER_CODE: # bind this name print("Other HTTP code") To me these read better than the punctuation characters. But I guess some folks have suggested enlisting 'as', which is a word, of course. -- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th.

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The semantics of pattern matching for Python
by Mark Shannon Nov. 23, 2020

Nov. 23, 2020

Hi everyone, There has been much discussion on the syntax of pattern matching for Python (in case you hadn't noticed ;) Unfortunately the semantics seem to have been somewhat overlooked. What pattern matching actually does seems at least as important as the syntax. I believe that a pattern matching implementation must have the following properties: * The semantics must be precisely defined. * It must be implemented efficiently. * Failed matches must not pollute the enclosing namespace. * Objects should be able determine which patterns they match. * It should be able to handle erroneous patterns, beyond just syntax errors. PEP 634 and PEP 642 don't have *any* of these properties. I've written up a document to specify a possible semantics of pattern matching for Python that has the above properties, and includes reasons why they are necessary. https://github.com/markshannon/pattern-matching/blob/master/precise_semanti… It's in the format of a PEP, but it isn't a complete PEP as it lacks surface syntax. Please, let me know what you think. Cheers, Mark.

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Matching syntax and semantics
by Eric Nieuwland Nov. 23, 2020

Nov. 23, 2020

Hi all, Some days back Mark Shannon posted his view/proposal pattern matching on github. While reading it I realised an intermediate step between matching and variable assignment might do away with part of the discussion. I wrote it in an issue with the view/proposal (https://github.com/markshannon/pattern-matching/issues/1) Thinking about it a bit longer, it really might be worth exploring the idea more, so let me repeat it here: 1. In a pattern the values to match are marked with a special symbol (‘$’, ‘!’ or ‘?’ seem candidates). 2. A matching case produces a tuple of matched values. The tuple may be nested to reflect the matched structure. 3. The tuple may be deconstructed according to the usual rules. As an example: example_value = Example("bar", Embedded(None, "foo"), 42, "baz") match example_value: case Example($, Embedded($, "foo"), 42, $) as t: # t = ("bar”, (None, ), "baz”) pass case Example($, Embedded($, "foo"), 42, $) as pre, *rest: # pre = "bar", rest = ((None, ), "baz”) pass alternatively: match example_value: case pre, *rest = t = Example($, Embedded($, "foo"), 42, $): # pre = "bar", rest = ((None, ), "baz”) # t = ("bar”, (None, ), "baz”) pass Just my $0.02 —eric

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Summary of Python tracker Issues
by Python tracker Nov. 20, 2020

Nov. 20, 2020

ACTIVITY SUMMARY (2020-11-13 - 2020-11-20) 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 7593 (-35) closed 46562 (+103) total 54155 (+68) Open issues with patches: 3061 Issues opened (52) ================== #25710: zipimport is not PEP 3147 or PEP 488 compliant https://bugs.python.org/issue25710 reopened by brett.cannon #41561: test_ssl fails in Ubuntu 20.04: test_min_max_version_mismatch https://bugs.python.org/issue41561 reopened by christian.heimes #42296: Infinite loop uninterruptable on Windows in 3.10 https://bugs.python.org/issue42296 reopened by eryksun #42352: A string representation of slice objects with colon syntax https://bugs.python.org/issue42352 opened by rossbar #42353: Proposal: re.prefixmatch method (alias for re.match) https://bugs.python.org/issue42353 opened by gregory.p.smith #42355: symtable: get_namespace doesn't check whether if there are mul https://bugs.python.org/issue42355 opened by BTaskaya #42356: Dict inline manipulations https://bugs.python.org/issue42356 opened by tomek.hlawiczka #42357: Wrong Availability for signal.SIGCHLD https://bugs.python.org/issue42357 opened by myzhang1029 #42358: Python 3.9.0 unable to detect ax_cv_c_float_words_bigendian va https://bugs.python.org/issue42358 opened by blastwave #42360: In the namedtuple documentation, mention that typename should https://bugs.python.org/issue42360 opened by alegonz #42361: Use Tcl/Tk 8.6.10 in build-installer.py when building on recen https://bugs.python.org/issue42361 opened by ronaldoussoren #42362: Switch to clang as default compiler in build-installer.py https://bugs.python.org/issue42362 opened by ronaldoussoren #42363: I think it will be better to output self._state for debugging https://bugs.python.org/issue42363 opened by jimlinntu #42367: Restore os.makedirs ability to apply mode to all directories c https://bugs.python.org/issue42367 opened by gregory.p.smith #42369: Reading ZipFile not thread-safe https://bugs.python.org/issue42369 opened by Thomas #42370: test_ttk_guionly: test_to() fails on the GitHub Ubuntu job https://bugs.python.org/issue42370 opened by vstinner #42371: datetime.fromisoformat(): Omitted colon in timezone suffix rai https://bugs.python.org/issue42371 opened by Bengt.Lüers #42373: PEP 626 does not specify behavior of tracing for keywords. https://bugs.python.org/issue42373 opened by Mark.Shannon #42375: subprocess DragonFlyBSD build update https://bugs.python.org/issue42375 opened by devnexen #42376: Add helpers to populate modules in C https://bugs.python.org/issue42376 opened by christian.heimes #42377: allow typing.cast with TYPE_CHECKING https://bugs.python.org/issue42377 opened by dpinol #42378: logging reopens file with same mode, possibly truncating https://bugs.python.org/issue42378 opened by ecatmur2 #42380: Build windows binaries with MS VS2019 16.8+ / MSVC 19.28+ https://bugs.python.org/issue42380 opened by h-vetinari #42382: No easy way to get the distribution which provided a importlib https://bugs.python.org/issue42382 opened by s0undt3ch #42383: Pdb does not correclty restart the target if it changes the cu https://bugs.python.org/issue42383 opened by hexagonrecursion #42384: Inconsistent sys.path between python and pdb https://bugs.python.org/issue42384 opened by hexagonrecursion #42385: Should enum.auto's behavior be adjusted for StrEnum to return https://bugs.python.org/issue42385 opened by Antony.Lee #42386: Update icons for macOS 11 https://bugs.python.org/issue42386 opened by 17jiangz1 #42387: Pdb should restore the execution environment before reexecutin https://bugs.python.org/issue42387 opened by hexagonrecursion #42388: subprocess.check_output(['echo', 'test'], text=True, input=Non https://bugs.python.org/issue42388 opened by ThiefMaster #42389: test_multiprocessing: @requires_hashdigest() prevents test dis https://bugs.python.org/issue42389 opened by christian.heimes #42390: Other Python implementations may not expose the module name in https://bugs.python.org/issue42390 opened by wmeehan #42391: Clarify documentation of TestCase.assertIs https://bugs.python.org/issue42391 opened by cool-RR #42392: remove the 'loop' parameter from __init__ in all classes in as https://bugs.python.org/issue42392 opened by yselivanov #42393: Raise overflow errors iso. deprecation warnings in socket.hton https://bugs.python.org/issue42393 opened by erlendaasland #42395: aclosing was not added to __all__ in contextlib https://bugs.python.org/issue42395 opened by tomgrin10 #42401: Plislit does not handle date timezone correctly https://bugs.python.org/issue42401 opened by jcbertin #42402: Termios module documentation is extremely lacking https://bugs.python.org/issue42402 opened by dan.merillat #42404: clinic: add option to pass module object to converter function https://bugs.python.org/issue42404 opened by christian.heimes #42405: Add distutils mvsccompiler support for Windows ARM64 build https://bugs.python.org/issue42405 opened by avladu #42406: Importing multiprocessing breaks pickle.whichmodule https://bugs.python.org/issue42406 opened by renatolfc #42407: Grammatical typo in multiprocessing doc https://bugs.python.org/issue42407 opened by arioa #42408: passing memoryview slice to struct packing functions https://bugs.python.org/issue42408 opened by danielhrisca #42409: Interpreter exit blocks waiting for ThreadPoolExecutor.map https://bugs.python.org/issue42409 opened by gsakkis #42410: Raise a pickleError when convert _functools module to use PyTy https://bugs.python.org/issue42410 opened by shihai1991 #42411: respect cgroups limits when trying to allocate memory https://bugs.python.org/issue42411 opened by caarlos0 #42412: Fix bases issues in PyType_FromModuleAndSpec() https://bugs.python.org/issue42412 opened by serhiy.storchaka #42414: unable to document fields of dataclass https://bugs.python.org/issue42414 opened by jmg #42415: python3.lib in Python3.9.0 Windows distribution does not conta https://bugs.python.org/issue42415 opened by David Hewitt #42417: Empty body {} in POST requests leads to 405 Method not allowed https://bugs.python.org/issue42417 opened by bhushan.shelke #42418: PyType_GetModule() should warn/fail when type has Py_TPFLAGS_B https://bugs.python.org/issue42418 opened by christian.heimes #42419: Typo in "what's new in Python 3.9" https://bugs.python.org/issue42419 opened by hiqua Most recent 15 issues with no replies (15) ========================================== #42419: Typo in "what's new in Python 3.9" https://bugs.python.org/issue42419 #42418: PyType_GetModule() should warn/fail when type has Py_TPFLAGS_B https://bugs.python.org/issue42418 #42412: Fix bases issues in PyType_FromModuleAndSpec() https://bugs.python.org/issue42412 #42411: respect cgroups limits when trying to allocate memory https://bugs.python.org/issue42411 #42409: Interpreter exit blocks waiting for ThreadPoolExecutor.map https://bugs.python.org/issue42409 #42408: passing memoryview slice to struct packing functions https://bugs.python.org/issue42408 #42407: Grammatical typo in multiprocessing doc https://bugs.python.org/issue42407 #42406: Importing multiprocessing breaks pickle.whichmodule https://bugs.python.org/issue42406 #42404: clinic: add option to pass module object to converter function https://bugs.python.org/issue42404 #42401: Plislit does not handle date timezone correctly https://bugs.python.org/issue42401 #42393: Raise overflow errors iso. deprecation warnings in socket.hton https://bugs.python.org/issue42393 #42391: Clarify documentation of TestCase.assertIs https://bugs.python.org/issue42391 #42389: test_multiprocessing: @requires_hashdigest() prevents test dis https://bugs.python.org/issue42389 #42388: subprocess.check_output(['echo', 'test'], text=True, input=Non https://bugs.python.org/issue42388 #42387: Pdb should restore the execution environment before reexecutin https://bugs.python.org/issue42387 Most recent 15 issues waiting for review (15) ============================================= #42419: Typo in "what's new in Python 3.9" https://bugs.python.org/issue42419 #42415: python3.lib in Python3.9.0 Windows distribution does not conta https://bugs.python.org/issue42415 #42412: Fix bases issues in PyType_FromModuleAndSpec() https://bugs.python.org/issue42412 #42410: Raise a pickleError when convert _functools module to use PyTy https://bugs.python.org/issue42410 #42406: Importing multiprocessing breaks pickle.whichmodule https://bugs.python.org/issue42406 #42405: Add distutils mvsccompiler support for Windows ARM64 build https://bugs.python.org/issue42405 #42401: Plislit does not handle date timezone correctly https://bugs.python.org/issue42401 #42395: aclosing was not added to __all__ in contextlib https://bugs.python.org/issue42395 #42393: Raise overflow errors iso. deprecation warnings in socket.hton https://bugs.python.org/issue42393 #42392: remove the 'loop' parameter from __init__ in all classes in as https://bugs.python.org/issue42392 #42391: Clarify documentation of TestCase.assertIs https://bugs.python.org/issue42391 #42390: Other Python implementations may not expose the module name in https://bugs.python.org/issue42390 #42386: Update icons for macOS 11 https://bugs.python.org/issue42386 #42384: Inconsistent sys.path between python and pdb https://bugs.python.org/issue42384 #42383: Pdb does not correclty restart the target if it changes the cu https://bugs.python.org/issue42383 Top 10 most discussed issues (10) ================================= #1635741: Py_Finalize() doesn't clear all Python objects at exit https://bugs.python.org/issue1635741 21 msgs #42392: remove the 'loop' parameter from __init__ in all classes in as https://bugs.python.org/issue42392 15 msgs #40939: Remove the old parser https://bugs.python.org/issue40939 11 msgs #42323: [AIX] test_math: test_nextafter(float('nan'), 1.0) does not re https://bugs.python.org/issue42323 10 msgs #40998: Compiler warnings in ubsan builds https://bugs.python.org/issue40998 9 msgs #42202: Optimize function annotation https://bugs.python.org/issue42202 8 msgs #42102: Make builtins.callable "generic" https://bugs.python.org/issue42102 7 msgs #42318: [tkinter] surrogate pairs in Tcl/Tk string when pasting an emo https://bugs.python.org/issue42318 7 msgs #25053: Possible race condition in Pool https://bugs.python.org/issue25053 6 msgs #39573: [C API] Make PyObject an opaque structure in the limited C API https://bugs.python.org/issue39573 6 msgs Issues closed (93) ================== #6237: Build errors when using LDFLAGS="-Wl,--no-undefined" https://bugs.python.org/issue6237 closed by iritkatriel #11604: Have type(n,b,d) check for type(b[i]) is module https://bugs.python.org/issue11604 closed by serhiy.storchaka #12726: explain that locale.getlocale() does not read system's locales https://bugs.python.org/issue12726 closed by iritkatriel #13561: os.listdir documentation should mention surrogateescape https://bugs.python.org/issue13561 closed by vstinner #13892: distutils handling of windows manifest isn't optimal https://bugs.python.org/issue13892 closed by iritkatriel #14531: Backtrace should not attempt to open <stdin> file https://bugs.python.org/issue14531 closed by iritkatriel #14643: Security page out of date https://bugs.python.org/issue14643 closed by vstinner #15263: Guard against invalid file handles in os functions https://bugs.python.org/issue15263 closed by eryksun #15479: Allow MAX_STRING_LENGTH limits to be changed at runtime https://bugs.python.org/issue15479 closed by iritkatriel #15653: PEP 3121, 384 refactoring applied to hashopenssl module https://bugs.python.org/issue15653 closed by vstinner #15665: PEP 3121, 384 refactoring applied to lsprof module https://bugs.python.org/issue15665 closed by vstinner #15668: PEP 3121, 384 Refactoring applied to random module https://bugs.python.org/issue15668 closed by vstinner #15670: PEP 3121, 384 Refactoring applied to ssl module https://bugs.python.org/issue15670 closed by vstinner #15671: PEP 3121, 384 Refactoring applied to struct module https://bugs.python.org/issue15671 closed by vstinner #15675: PEP 3121, 384 Refactoring applied to array module https://bugs.python.org/issue15675 closed by vstinner #15697: PEP 3121 refactoring applied to pwd module https://bugs.python.org/issue15697 closed by vstinner #15705: PEP 3121, 384 Refactoring applied to sha256 module https://bugs.python.org/issue15705 closed by vstinner #15707: PEP 3121, 384 Refactoring applied to signal module https://bugs.python.org/issue15707 closed by vstinner #15714: PEP 3121, 384 Refactoring applied to grp module https://bugs.python.org/issue15714 closed by vstinner #15734: PEP 3121, 384 Refactoring applied to spwd module https://bugs.python.org/issue15734 closed by vstinner #17183: Small enhancements to Lib/_markupbase.py https://bugs.python.org/issue17183 closed by iritkatriel #17808: No code example for Event object in threading module https://bugs.python.org/issue17808 closed by iritkatriel #17816: Weak*Dictionary KeyErrors during callbacks https://bugs.python.org/issue17816 closed by iritkatriel #17854: symmetric difference operation applicable to more than two set https://bugs.python.org/issue17854 closed by iritkatriel #18122: RuntimeError: not holding the import lock https://bugs.python.org/issue18122 closed by iritkatriel #18838: The order of interactive prompt and traceback on Windows https://bugs.python.org/issue18838 closed by iritkatriel #20582: socket.getnameinfo() does not document flags https://bugs.python.org/issue20582 closed by iritkatriel #24886: open fails randomly on AIX https://bugs.python.org/issue24886 closed by methane #26067: test_shutil fails when gid name is missing https://bugs.python.org/issue26067 closed by iritkatriel #27119: `compile` doesn't compile into an AST object as specified https://bugs.python.org/issue27119 closed by BTaskaya #33074: dbm corrupts index on macOS (_dbm module) https://bugs.python.org/issue33074 closed by ronaldoussoren #34364: problem with traceback for syntax error in f-string https://bugs.python.org/issue34364 closed by iritkatriel #35498: Parents objects in pathlib.Path don't support slices as __geti https://bugs.python.org/issue35498 closed by p-ganssle #35847: RISC-V needs CTYPES_PASS_BY_REF_HACK https://bugs.python.org/issue35847 closed by iritkatriel #36520: Email header folded incorrectly https://bugs.python.org/issue36520 closed by iritkatriel #37205: time.perf_counter() is not system-wide on Windows, in disagree https://bugs.python.org/issue37205 closed by vstinner #37733: Fail to build _curses module of Python 3.7.4 on AIX 7.1 using https://bugs.python.org/issue37733 closed by christian.heimes #37737: mmap module track anonymous page on macOS https://bugs.python.org/issue37737 closed by ronaldoussoren #38320: Clarify unittest expectedFailure behaviour in the documentatio https://bugs.python.org/issue38320 closed by iritkatriel #38495: print built-in function docs bug https://bugs.python.org/issue38495 closed by mdk #38506: Launcher for Windows (py.exe) may rank Python 3.xx (in the fut https://bugs.python.org/issue38506 closed by steve.dower #39411: pyclbr rewrite using AST https://bugs.python.org/issue39411 closed by BTaskaya #39463: ast.Constant, bytes, and ast.unparse https://bugs.python.org/issue39463 closed by BTaskaya #40656: Clean up detect_socket() in setup.py https://bugs.python.org/issue40656 closed by ned.deily #40754: Test installers before releasing (ModuleNotFoundErrors) https://bugs.python.org/issue40754 closed by steve.dower #40891: Use PEP 573 in functools https://bugs.python.org/issue40891 closed by shihai1991 #41001: Provide wrapper for eventfd https://bugs.python.org/issue41001 closed by christian.heimes #41625: Add splice() to the os module https://bugs.python.org/issue41625 closed by pablogsal #41686: C++ Embedded 'time.sleep()' is not working on Windows host due https://bugs.python.org/issue41686 closed by vstinner #41713: _signal module leak: test_interpreters leaked [1424, 1422, 142 https://bugs.python.org/issue41713 closed by vstinner #41741: test_peg_generator timed out (25 min) on x86 Gentoo Non-Debug https://bugs.python.org/issue41741 closed by vstinner #41861: Convert sqlite3 to heap types (PEP 384) https://bugs.python.org/issue41861 closed by erlendaasland #42085: Add dedicated slot for sending values https://bugs.python.org/issue42085 closed by yselivanov #42087: Remove pre-AIX 6.1 dead code paths https://bugs.python.org/issue42087 closed by vstinner #42153: doc: library imaplib a url not available https://bugs.python.org/issue42153 closed by gvanrossum #42173: Drop Solaris support https://bugs.python.org/issue42173 closed by vstinner #42231: test_zipimport failure https://bugs.python.org/issue42231 closed by vstinner #42264: Deprecate or remove sqlite3.OptimizedUnicode https://bugs.python.org/issue42264 closed by serhiy.storchaka #42287: Use Py_NewRef & Py_XNewRef where applicable https://bugs.python.org/issue42287 closed by vstinner #42290: Display of Unicode strings with bidi characters https://bugs.python.org/issue42290 closed by terry.reedy #42293: Installation of pyinstaller in Windows fails with utf8 error https://bugs.python.org/issue42293 closed by terry.reedy #42302: [Turtle] Add clockwise and anticlockwise method as alias to ri https://bugs.python.org/issue42302 closed by zenr #42317: Docs of `typing.get_args`: Mention that due to caching of typi https://bugs.python.org/issue42317 closed by gvanrossum #42330: Add browsh in the webbrowser module https://bugs.python.org/issue42330 closed by terry.reedy #42332: add __weakref__ to types.GenericAlias https://bugs.python.org/issue42332 closed by gvanrossum #42334: Subclassing int and complex with keyword arguments weird https://bugs.python.org/issue42334 closed by terry.reedy #42335: Python Crashes Exception code 0xc0000374 ntdll.dll https://bugs.python.org/issue42335 closed by strantor #42339: official embedded Python fails to import certain modules https://bugs.python.org/issue42339 closed by steve.dower #42344: SimpleNamespace: update documentation regarding comparison https://bugs.python.org/issue42344 closed by eric.smith #42345: Equality of typing.Literal depends on the order of arguments https://bugs.python.org/issue42345 closed by gvanrossum #42350: Calling os.fork() at Python exit logs: AttributeError: 'NoneTy https://bugs.python.org/issue42350 closed by vstinner #42351: Setup.py: UnicodeDecodeError in grep_headers_for https://bugs.python.org/issue42351 closed by epaine #42354: Tuple unpacking with * causes SyntaxError in with ... as ... https://bugs.python.org/issue42354 closed by BTaskaya #42359: tutorial: list is a class https://bugs.python.org/issue42359 closed by rhettinger #42364: Typo in french doc translation https://bugs.python.org/issue42364 closed by xtreak #42365: Python launcher: sort order in "Installed versions" off with 3 https://bugs.python.org/issue42365 closed by gvanrossum #42366: Use MSVC2019 and /Ob3 option to compile Windows builds https://bugs.python.org/issue42366 closed by malin #42368: Make set ordered https://bugs.python.org/issue42368 closed by rhettinger #42372: A crash in do_richcompare https://bugs.python.org/issue42372 closed by kuraga #42374: Unparenthesized walrus is not allowed in genexps https://bugs.python.org/issue42374 closed by lys.nikolaou #42379: Optional List Args Persist Across Objects https://bugs.python.org/issue42379 closed by eric.smith #42381: Allow unparenthesized walrus in set comprehensions https://bugs.python.org/issue42381 closed by lys.nikolaou #42394: Exception handling on boolean comparisons https://bugs.python.org/issue42394 closed by steven.daprano #42396: Add a whatsnew entry about async contextlib.nullcontext https://bugs.python.org/issue42396 closed by asvetlov #42397: lstrip 处理出现bug https://bugs.python.org/issue42397 closed by christian.heimes #42398: Race condition in "make regen-all" when running jobs in parall https://bugs.python.org/issue42398 closed by vstinner #42399: Error upon pip usage. https://bugs.python.org/issue42399 closed by alki284 #42400: Ubuntu tests hangs on test_ttk_guionly and test_heading_callba https://bugs.python.org/issue42400 closed by christian.heimes #42403: Cleanup importlib code https://bugs.python.org/issue42403 closed by vstinner #42413: Replace custom exception socket.timeout with TimeoutError https://bugs.python.org/issue42413 closed by christian.heimes #42416: IDLE calltip.get_argspec: use inspect.getdoc, comment fob https://bugs.python.org/issue42416 closed by terry.reedy #1374063: Broader iterable support for xmlrpclib https://bugs.python.org/issue1374063 closed by iritkatriel #1465554: Cygwin installer should create a link to libpythonX.Y.dll.a https://bugs.python.org/issue1465554 closed by iritkatriel

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Preconditions for accepting any pattern matching PEP
by Mark Shannon Nov. 20, 2020

Nov. 20, 2020

Hi, I'd like to request that any pattern matching PEP and its implementation meet certain standards before acceptance. As one of the maintainers of the AST-to-bytecode part of the compiler and the bytecode interpreter, I don't want to be in the situation where we are forced to accept a sub-standard implementation because a PEP has been accepted and the PEP authors are unable, or unwilling, to produce an implementation that is of a sufficiently high standard. Therefore, I would ask the steering committee to require the following as a minimum before formal acceptance of any pattern matching PEP. 1. The semantics must be well defined. 2. There should be no global side-effects in the bytecode. 3. Each bytecode should perform a single, reasonably limited, operation. 4. There should be a clear path, using known compiler optimization techniques to making it efficient, if it is not initially so. 1. We want to be able to change the implementation. The current (3.9+) compiler produces quite clean bytecode for "try-finally" and "with" statements. Earlier implementations of the compiler were simplistic and required quite convoluted bytecodes in the interpreter. We were able to make these improvements because the "try-finally" and "with" statements are well specified, so we could reason about changes to the implementation. Should the old and new implementations have differed, it was possible to refer to the language documentation to determine which was correct. Without well defined semantics, the first implementation of pattern matching becomes the de-facto semantics, with all of its corner cases. Reasoning about changes becomes almost impossible. 2. The implementation of PEP 634 can import "abc.collections" mid bytecode. I don't look forward to the bug reports when the module can't be imported for some unrelated reason and pattern matching fails. We recently added the `LOAD_ASSERTION_ERROR` bytecode to ensure that asserts work even after `del builtins.AssertionError`. We should maintain this level of robustness. 3. This comes down to reasoning about whether the compiler is correct, and interpreter performance. Admittedly, the current bytecodes don't always adhere to the above rule, but they mostly do and I don't want the situation to deteriorate. The implementation of PEP 634 includes a number of bytecodes that implement their own mini-interpreters within. It is the job of the compiler, not the interpreter, to handle such control flow. 4. If pattern matching is added to the language, and it becomes popular, we don't want it to be slow. Knowing that there exists an efficient implementation, and how to achieve it, is important. Ideally the initial implementation should be efficient, but knowing that it could be is sufficient for acceptance. Cheers, Mark.

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PEP 642: Constraint Pattern Syntax for Structural Pattern Matching
by Nick Coghlan Nov. 20, 2020

Nov. 20, 2020

Hi folks, This is a mailing list repost of the Discourse thread at https://discuss.python.org/t/pep-642-constraint-pattern-syntax-for-structur… The rendered version of the PEP can be found here: https://www.python.org/dev/peps/pep-0642/ The full text is also quoted in the Discourse thread. The remainder of this email is the same introduction that I posted on Discourse. I’m largely a fan of the Structural Pattern Matching proposal in PEP 634, but there’s one specific piece of the syntax proposal that I strongly dislike: the idea of basing the distinction between capture patterns and value patterns purely on whether they use a simple name or a dotted name. Thus PEP 642, which retains most of PEP 634 unchanged, but adjusts value checks to use an explicit prefix syntax (either `?EXPR` for equality constraints, or `?is EXPR` for identity constraints), rather than relying on users learning that literals and attribute lookups in a capture pattern mean a value lookup check, while simple names mean a capture pattern (unlike both normal expressions, where all three mean a value lookup, and assignment targets, where both simple and dotted names bind a new reference). The PEP itself has a lot of words explaining why I’ve made the design decisions I have, as well as the immediate and potential future benefits offered by using an explicit prefix syntax for value constraints, but the super short form goes like this: * if you don’t like match statements at all, or wish we were working on designing a C-style switch statement instead, then PEP 642 isn’t going to appeal to you any more than PEP 634 does * if, like me, you don’t like the idea of breaking the existing property of Python that caching the result of a value lookup subexpression in a local variable and then using that variable in place of the original subexpression should “just work”, then PEP 642’s explicit constraint prefix syntax may be more to your liking * however, if the idea of the `?` symbol becoming part of Python’s syntax doesn’t appeal to you, then you may consider any improved clarity of intent that PEP 642 might offer to not be worth that cost Cheers, Nick. -- Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia

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How Cpython repository has a pre-commit hook ? (as in PEP8)
by Nilo César Teixeira Nov. 19, 2020

Nov. 19, 2020

Hello, I'm not a Python contributor but I have a question which (I believe) can be answered here, so I've subscribed. The question is at stackoverflow: https://stackoverflow.com/questions/64912716/are-pre-commit-hooks-clonable After some research the only thing similtar to a git pre-commit hook I could find on the cpython repo was the patchcheck.py script on github.com/python/cpython/tree/master/Tools/scripts (patchcheck.py), which runs in Travis. Is this the pre-commit hook PEP8 talks about ? Thanks for your help and attention. -- *Nilo César Teixeira* nilo.teixeira(a)gmail.com (55) (11) 98571-5314

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