Mailman 3 June 2019 - Python-Dev

Documenting METH_FASTCALL
by Jeroen Demeyer June 13, 2019

June 13, 2019

Hello, has the time come to document METH_FASTCALL? This was introduced in Python 3.6 for positional arguments only and extended in Python 3.7 to support also keyword arguments. No changes have been made since then. The vectorcall protocol (PEP 590) uses a calling convention based on METH_FASTCALL, so I expect METH_FASTCALL to stay as it is. PEP 590 also means that CPython is now even more than before optimized for METH_FASTCALL instead of METH_VARARGS. Whether or not METH_FASTCALL … [View More]

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Parser module in the stdlib
by Pablo Galindo Salgado June 13, 2019

June 13, 2019

Hi everyone, TLDR ===== I propose to remove the current parser module and expose pgen2 as a standard library module. Some context =========== The parser module has been "deprecated" (technically we recommend to prefer the ast module instead) since Python2.5 but is still in the standard library. Is a 1222-line C module that needs to be kept in sync with the grammar and the Python parser sometimes by hand. It has also been broken for several years: I recently fixed a bug that was introduced … [View More]in Python 3.5 that caused the parse module to not being able to parse if-else blocks ( https://bugs.python.org/issue36256). The interface it provides is a very raw view of the CST. For instance: >>> parser.sequence2st(parser.suite("def f(x,y,z): pass").totuple()) provides an object with methods compile, isexpr, issuite, tolist, totuple. The last two produce containers with the numerical values of the grammar elements (tokens, dfas...etc) >>> parser.suite("def f(x,y,z): pass").tolist() [257, [269, [295, [263, [1, 'def'], [1, 'f'], [264, [7, '('], [265, [266, [1, 'x']], [12, ','], [266, [1, 'y']], [12, ','], [266, [1, 'z']]], [8, ')']], [11, ':'], [304, [270, [271, [277, [1, 'pass']]], [4, '']]]]]], [4, ''], [0, '']] This is a very raw interface and is very tied to the particularities of CPython without almost any abstraction. On the other hand, there is a Python implementation of the Python parser and parser generator in lib2to3 (pgen2). This module is not documented and is usually considered an implementation detail of lib2to3 but is extremely useful. Several 3rd party packages (black, fissix...) are using it directly or have their own forks due to the fact that it can get outdated with respect to the Python3 grammar as it was originally used only for Python2 to Python3 migration. It has the ability to consume LL1 grammars in EBNF form and produces an LL1 parser for them (by creating parser tables that the same module can consume). Many people use the module currently to support or parse supersets of Python (like Python2/3 compatible grammars, cython-like changes...etc). Proposition ======== I propose to remove finally the parser module as it has been "deprecated" for a long time, is almost clear that nobody uses it and has very limited usability and replace it (maybe with a different name) with pgen2 (maybe with a more generic interface that is detached to lib2to3 particularities). This will not only help a lot current libraries that are using forks or similar solutions but also will help to keep synchronized the shipped grammar (that is able to parse Python2 and Python3 code) with the current Python one (as now will be more justified to keep them in sync). What do people think about? Do you have any concerns? Do you think is a good/bad idea? Regards from sunny London, Pablo Galindo [View Less]

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Using Generic Type Constructors at Runtime
by Saul Shanabrook June 12, 2019

June 12, 2019

Hello all, I am working on an expression and replacement system in Python and am trying to figure out if constructors for generic classes should be done with classmethods or with functions. I have laid out an example using each in a Github issue (https://github.com/Quansight-Labs/metadsl/issues/69#issuecomment-500898932) and wanted to open the issue up the larger community because I am unsure if there is an established pattern here yet. A minimal example showing the difference is `none(int)` … [View More]

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1 PR, multiple issues
by Jeffrey Kintscher June 11, 2019

June 11, 2019

When I create a PR that resolves multiple issues, should I add it to each issue, or just to one issue and add relevant comments to the others? //Jeff -- ----------------------------------------- From there to here, from here to there, funny things are everywhere. -- Theodore Geisel

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Enum and annotations
by Ethan Furman June 11, 2019

June 11, 2019

Greetings! I saw my first annotation mix-up with regards to Enum today: https://stackoverflow.com/q/56532591/208880 #enum import: from enum import Enum # enum definition: class Status(Enum): on: 1 off: 2 My question for the group: Is this worth "fixing" or should I leave it alone? On the one hand it seems like an obvious error, but on the other I hate getting in the way of needs I haven't thought of. -- ~Ethan~

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Using vectorcall for tp_new and tp_init
by Jeroen Demeyer June 9, 2019

June 9, 2019

Hello, I'm starting this thread to brainstorm for using vectorcall to speed up creating instances of Python classes. Currently the following happens when creating an instance of a Python class X using X(.....) and assuming that __new__ and __init__ are Python functions and that the metaclass of X is simply "type": 1. type_call (the tp_call wrapper for type) is invoked with arguments (X, args, kwargs). 2. type_call calls slot_tp_new with arguments (X, args, kwargs). 3. slot_tp_new calls … [View More]

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Question on handling of per-thread async exception with global pending.async_exc flag
by Xintong Zhou June 8, 2019

June 8, 2019

Hi, I am trying to understand the way that async exceptions are handled between _PyEval_EvalFrameDefault (in ceval.c) and PyThreadState_SetAsyncExc (pystate.c). In ceval.c, the eval loop determines whether to check for async exception for the current thread based on the global _PyRuntime.ceval.eval_breaker, which takes the global _PyRuntime.ceval.pending.async_exc as a factor ( source <https://github.com/python/cpython/blob/ef4ec6ed12d6c6200a85068f60483723298b…> ). It feels to me that … [View More]

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python-ideas and python-dev migrated to Mailman 3/HyperKitty
by Victor Stinner June 8, 2019

June 8, 2019

Hi, Our kind postmasters Mark Sapiro and Abhilash Raj migrated python-ideas and python-dev mailing lists from Mailman 2 to Mailman 3 (running on Python 3 ;-))! You can now enjoy HyperKitty, the new web UI to access the mailing lists: https://mail.python.org/archives/list/python-dev@python.org/ and https://mail.python.org/archives/list/python-ideas@python.org/ Enhancements: * Ability to post an email directly on the web UI (open a new topic or reply to an existing topic) * Nicer "… [View More]

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Summary of Python tracker Issues
by Python tracker June 7, 2019

June 7, 2019

ACTIVITY SUMMARY (2019-05-31 - 2019-06-07) 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 7007 (-21) closed 41943 (+104) total 48950 (+83) Open issues with patches: 2817 Issues opened (51) ================== #21492: email.header.decode_header sometimes returns bytes, sometimes https://bugs.python.org/issue21492 reopened by ezio.melotti #32912: … [View More]

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PEP 596 proposes doubling the release cadence
by Łukasz Langa June 7, 2019

June 7, 2019

PEP body and discussion link: https://discuss.python.org/t/pep-596-python-3-9-release-schedule-doubling-t… - Ł

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