Mailman 3 June 2019 - Python-Dev

PEP 1, PEP Purpose and Guidelines
by barry＠zope.com 18 May '21

18 May '21

It has been a while since I posted a copy of PEP 1 to the mailing lists and newsgroups. I've recently done some updating of a few sections, so in the interest of gaining wider community participation in the Python development process, I'm posting the latest revision of PEP 1 here. A version of the PEP is always available on-line at http://www.python.org/peps/pep-0001.html Enjoy, -Barry -------------------- snip snip -------------------- PEP: 1 Title: PEP Purpose and Guidelines Version: $Revision: 1.36 $ Last-Modified: $Date: 2002/07/29 18:34:59 $ Author: Barry A. Warsaw, Jeremy Hylton Status: Active Type: Informational Created: 13-Jun-2000 Post-History: 21-Mar-2001, 29-Jul-2002 What is a PEP? PEP stands for Python Enhancement Proposal. A PEP is a design document providing information to the Python community, or describing a new feature for Python. The PEP should provide a concise technical specification of the feature and a rationale for the feature. We intend PEPs to be the primary mechanisms for proposing new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python. The PEP author is responsible for building consensus within the community and documenting dissenting opinions. Because the PEPs are maintained as plain text files under CVS control, their revision history is the historical record of the feature proposal[1]. Kinds of PEPs There are two kinds of PEPs. A standards track PEP describes a new feature or implementation for Python. An informational PEP describes a Python design issue, or provides general guidelines or information to the Python community, but does not propose a new feature. Informational PEPs do not necessarily represent a Python community consensus or recommendation, so users and implementors are free to ignore informational PEPs or follow their advice. PEP Work Flow The PEP editor, Barry Warsaw <peps(a)python.org>, assigns numbers for each PEP and changes its status. The PEP process begins with a new idea for Python. It is highly recommended that a single PEP contain a single key proposal or new idea. The more focussed the PEP, the more successfully it tends to be. The PEP editor reserves the right to reject PEP proposals if they appear too unfocussed or too broad. If in doubt, split your PEP into several well-focussed ones. Each PEP must have a champion -- someone who writes the PEP using the style and format described below, shepherds the discussions in the appropriate forums, and attempts to build community consensus around the idea. The PEP champion (a.k.a. Author) should first attempt to ascertain whether the idea is PEP-able. Small enhancements or patches often don't need a PEP and can be injected into the Python development work flow with a patch submission to the SourceForge patch manager[2] or feature request tracker[3]. The PEP champion then emails the PEP editor <peps(a)python.org> with a proposed title and a rough, but fleshed out, draft of the PEP. This draft must be written in PEP style as described below. If the PEP editor approves, he will assign the PEP a number, label it as standards track or informational, give it status 'draft', and create and check-in the initial draft of the PEP. The PEP editor will not unreasonably deny a PEP. Reasons for denying PEP status include duplication of effort, being technically unsound, not providing proper motivation or addressing backwards compatibility, or not in keeping with the Python philosophy. The BDFL (Benevolent Dictator for Life, Guido van Rossum) can be consulted during the approval phase, and is the final arbitrator of the draft's PEP-ability. If a pre-PEP is rejected, the author may elect to take the pre-PEP to the comp.lang.python newsgroup (a.k.a. python-list(a)python.org mailing list) to help flesh it out, gain feedback and consensus from the community at large, and improve the PEP for re-submission. The author of the PEP is then responsible for posting the PEP to the community forums, and marshaling community support for it. As updates are necessary, the PEP author can check in new versions if they have CVS commit permissions, or can email new PEP versions to the PEP editor for committing. Standards track PEPs consists of two parts, a design document and a reference implementation. The PEP should be reviewed and accepted before a reference implementation is begun, unless a reference implementation will aid people in studying the PEP. Standards Track PEPs must include an implementation - in the form of code, patch, or URL to same - before it can be considered Final. PEP authors are responsible for collecting community feedback on a PEP before submitting it for review. A PEP that has not been discussed on python-list(a)python.org and/or python-dev(a)python.org will not be accepted. However, wherever possible, long open-ended discussions on public mailing lists should be avoided. Strategies to keep the discussions efficient include, setting up a separate SIG mailing list for the topic, having the PEP author accept private comments in the early design phases, etc. PEP authors should use their discretion here. Once the authors have completed a PEP, they must inform the PEP editor that it is ready for review. PEPs are reviewed by the BDFL and his chosen consultants, who may accept or reject a PEP or send it back to the author(s) for revision. Once a PEP has been accepted, the reference implementation must be completed. When the reference implementation is complete and accepted by the BDFL, the status will be changed to `Final.' A PEP can also be assigned status `Deferred.' The PEP author or editor can assign the PEP this status when no progress is being made on the PEP. Once a PEP is deferred, the PEP editor can re-assign it to draft status. A PEP can also be `Rejected'. Perhaps after all is said and done it was not a good idea. It is still important to have a record of this fact. PEPs can also be replaced by a different PEP, rendering the original obsolete. This is intended for Informational PEPs, where version 2 of an API can replace version 1. PEP work flow is as follows: Draft -> Accepted -> Final -> Replaced ^ +----> Rejected v Deferred Some informational PEPs may also have a status of `Active' if they are never meant to be completed. E.g. PEP 1. What belongs in a successful PEP? Each PEP should have the following parts: 1. Preamble -- RFC822 style headers containing meta-data about the PEP, including the PEP number, a short descriptive title (limited to a maximum of 44 characters), the names, and optionally the contact info for each author, etc. 2. Abstract -- a short (~200 word) description of the technical issue being addressed. 3. Copyright/public domain -- Each PEP must either be explicitly labelled as placed in the public domain (see this PEP as an example) or licensed under the Open Publication License[4]. 4. Specification -- The technical specification should describe the syntax and semantics of any new language feature. The specification should be detailed enough to allow competing, interoperable implementations for any of the current Python platforms (CPython, JPython, Python .NET). 5. Motivation -- The motivation is critical for PEPs that want to change the Python language. It should clearly explain why the existing language specification is inadequate to address the problem that the PEP solves. PEP submissions without sufficient motivation may be rejected outright. 6. Rationale -- The rationale fleshes out the specification by describing what motivated the design and why particular design decisions were made. It should describe alternate designs that were considered and related work, e.g. how the feature is supported in other languages. The rationale should provide evidence of consensus within the community and discuss important objections or concerns raised during discussion. 7. Backwards Compatibility -- All PEPs that introduce backwards incompatibilities must include a section describing these incompatibilities and their severity. The PEP must explain how the author proposes to deal with these incompatibilities. PEP submissions without a sufficient backwards compatibility treatise may be rejected outright. 8. Reference Implementation -- The reference implementation must be completed before any PEP is given status 'Final,' but it need not be completed before the PEP is accepted. It is better to finish the specification and rationale first and reach consensus on it before writing code. The final implementation must include test code and documentation appropriate for either the Python language reference or the standard library reference. PEP Template PEPs are written in plain ASCII text, and should adhere to a rigid style. There is a Python script that parses this style and converts the plain text PEP to HTML for viewing on the web[5]. PEP 9 contains a boilerplate[7] template you can use to get started writing your PEP. Each PEP must begin with an RFC822 style header preamble. The headers must appear in the following order. Headers marked with `*' are optional and are described below. All other headers are required. PEP: <pep number> Title: <pep title> Version: <cvs version string> Last-Modified: <cvs date string> Author: <list of authors' real names and optionally, email addrs> * Discussions-To: <email address> Status: <Draft | Active | Accepted | Deferred | Final | Replaced> Type: <Informational | Standards Track> * Requires: <pep numbers> Created: <date created on, in dd-mmm-yyyy format> * Python-Version: <version number> Post-History: <dates of postings to python-list and python-dev> * Replaces: <pep number> * Replaced-By: <pep number> The Author: header lists the names and optionally, the email addresses of all the authors/owners of the PEP. The format of the author entry should be address(a)dom.ain (Random J. User) if the email address is included, and just Random J. User if the address is not given. If there are multiple authors, each should be on a separate line following RFC 822 continuation line conventions. Note that personal email addresses in PEPs will be obscured as a defense against spam harvesters. Standards track PEPs must have a Python-Version: header which indicates the version of Python that the feature will be released with. Informational PEPs do not need a Python-Version: header. While a PEP is in private discussions (usually during the initial Draft phase), a Discussions-To: header will indicate the mailing list or URL where the PEP is being discussed. No Discussions-To: header is necessary if the PEP is being discussed privately with the author, or on the python-list or python-dev email mailing lists. Note that email addresses in the Discussions-To: header will not be obscured. Created: records the date that the PEP was assigned a number, while Post-History: is used to record the dates of when new versions of the PEP are posted to python-list and/or python-dev. Both headers should be in dd-mmm-yyyy format, e.g. 14-Aug-2001. PEPs may have a Requires: header, indicating the PEP numbers that this PEP depends on. PEPs may also have a Replaced-By: header indicating that a PEP has been rendered obsolete by a later document; the value is the number of the PEP that replaces the current document. The newer PEP must have a Replaces: header containing the number of the PEP that it rendered obsolete. PEP Formatting Requirements PEP headings must begin in column zero and the initial letter of each word must be capitalized as in book titles. Acronyms should be in all capitals. The body of each section must be indented 4 spaces. Code samples inside body sections should be indented a further 4 spaces, and other indentation can be used as required to make the text readable. You must use two blank lines between the last line of a section's body and the next section heading. You must adhere to the Emacs convention of adding two spaces at the end of every sentence. You should fill your paragraphs to column 70, but under no circumstances should your lines extend past column 79. If your code samples spill over column 79, you should rewrite them. Tab characters must never appear in the document at all. A PEP should include the standard Emacs stanza included by example at the bottom of this PEP. A PEP must contain a Copyright section, and it is strongly recommended to put the PEP in the public domain. When referencing an external web page in the body of a PEP, you should include the title of the page in the text, with a footnote reference to the URL. Do not include the URL in the body text of the PEP. E.g. Refer to the Python Language web site [1] for more details. ... [1] http://www.python.org When referring to another PEP, include the PEP number in the body text, such as "PEP 1". The title may optionally appear. Add a footnote reference that includes the PEP's title and author. It may optionally include the explicit URL on a separate line, but only in the References section. Note that the pep2html.py script will calculate URLs automatically, e.g.: ... Refer to PEP 1 [7] for more information about PEP style ... References [7] PEP 1, PEP Purpose and Guidelines, Warsaw, Hylton http://www.python.org/peps/pep-0001.html If you decide to provide an explicit URL for a PEP, please use this as the URL template: http://www.python.org/peps/pep-xxxx.html PEP numbers in URLs must be padded with zeros from the left, so as to be exactly 4 characters wide, however PEP numbers in text are never padded. Reporting PEP Bugs, or Submitting PEP Updates How you report a bug, or submit a PEP update depends on several factors, such as the maturity of the PEP, the preferences of the PEP author, and the nature of your comments. For the early draft stages of the PEP, it's probably best to send your comments and changes directly to the PEP author. For more mature, or finished PEPs you may want to submit corrections to the SourceForge bug manager[6] or better yet, the SourceForge patch manager[2] so that your changes don't get lost. If the PEP author is a SF developer, assign the bug/patch to him, otherwise assign it to the PEP editor. When in doubt about where to send your changes, please check first with the PEP author and/or PEP editor. PEP authors who are also SF committers, can update the PEPs themselves by using "cvs commit" to commit their changes. Remember to also push the formatted PEP text out to the web by doing the following: % python pep2html.py -i NUM where NUM is the number of the PEP you want to push out. See % python pep2html.py --help for details. Transferring PEP Ownership It occasionally becomes necessary to transfer ownership of PEPs to a new champion. In general, we'd like to retain the original author as a co-author of the transferred PEP, but that's really up to the original author. A good reason to transfer ownership is because the original author no longer has the time or interest in updating it or following through with the PEP process, or has fallen off the face of the 'net (i.e. is unreachable or not responding to email). A bad reason to transfer ownership is because you don't agree with the direction of the PEP. We try to build consensus around a PEP, but if that's not possible, you can always submit a competing PEP. If you are interested assuming ownership of a PEP, send a message asking to take over, addressed to both the original author and the PEP editor <peps(a)python.org>. If the original author doesn't respond to email in a timely manner, the PEP editor will make a unilateral decision (it's not like such decisions can be reversed. :). References and Footnotes [1] This historical record is available by the normal CVS commands for retrieving older revisions. For those without direct access to the CVS tree, you can browse the current and past PEP revisions via the SourceForge web site at http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/python/nondist/peps/?cvsroot=… [2] http://sourceforge.net/tracker/?group_id=5470&atid=305470 [3] http://sourceforge.net/tracker/?atid=355470&group_id=5470&func=browse [4] http://www.opencontent.org/openpub/ [5] The script referred to here is pep2html.py, which lives in the same directory in the CVS tree as the PEPs themselves. Try "pep2html.py --help" for details. The URL for viewing PEPs on the web is http://www.python.org/peps/ [6] http://sourceforge.net/tracker/?group_id=5470&atid=305470 [7] PEP 9, Sample PEP Template http://www.python.org/peps/pep-0009.html Copyright This document has been placed in the public domain. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End:

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Boundaries between numbers and identifiers
by Serhiy Storchaka 15 Apr '21

15 Apr '21

In Python 2.5 `0or[]` was accepted by the Python parser. It became an error in 2.6 because "0o" became recognizing as an incomplete octal number. `1or[]` still is accepted. On other hand, `1if 2else 3` is accepted despites the fact that "2e" can be recognized as an incomplete floating point number. In this case the tokenizer pushes "e" back and returns "2". Shouldn't it do the same with "0o"? It is possible to make `0or[]` be parseable again. Python implementation is able to tokenize this example: $ echo '0or[]' | ./python -m tokenize 1,0-1,1: NUMBER '0' 1,1-1,3: NAME 'or' 1,3-1,4: OP '[' 1,4-1,5: OP ']' 1,5-1,6: NEWLINE '\n' 2,0-2,0: ENDMARKER '' On other hand, all these examples look weird. There is an assymmetry: `1or 2` is a valid syntax, but `1 or2` is not. It is hard to recognize visually the boundary between a number and the following identifier or keyword, especially if numbers can contain letters ("b", "e", "j", "o", "x") and underscores, and identifiers can contain digits. On both sides of the boundary can be letters, digits, and underscores. I propose to change the Python syntax by adding a requirement that there should be a whitespace or delimiter between a numeric literal and the following keyword.

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About "python-porting" mail list
by Facundo Batista 20 Jan '20

20 Jan '20

Hello! This list (which I co-admin, with Georg) is getting less and less traffic as months pass by. See: https://mail.python.org/pipermail/python-porting/ The interwebs has been collecting ton of resources about porting py2 to 3 during these years. Any not-yet-answered question surely can be done in a list with more participants. Can we kill this list? Thanks! Regards, -- . Facundo Blog: http://www.taniquetil.com.ar/plog/ PyAr: http://www.python.org.ar/ Twitter: @facundobatista

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Adding a toml module to the standard lib?
by Bastian Venthur 16 Dec '19

16 Dec '19

Hi, I'd like to discuss the idea to add a module to parse TOML [toml-lang] to Python's standard library. PEP-0518 -- Specifying Minimum Build System Requirements for Python Projects [pep] suggests to store build system dependencies in `pyproject.toml`, yet Python itself does not support this format. Various packaging related projects like pip and pipenv already support PEP-0518 and vendored one of the existing TOML libraries in order to read `pyproject.toml` files. Besides that, TOML seems a better alternative to .cfg/.ini, .json -- both of which are already supported by Python's standard lib and parsing/dumping TOML properly is tricky enough to solve it properly [requirements]. There are a couple of TOML implementations out there [toml, pytoml, tomlkit] and one would have to find out which one to prefer and migrate into the stdlib. If the result of this discussion is leaning towards adding TOML, I'd volunteer to do it. This includes: coordinating with the maintainer of the chosen library, writing the PEP (hopefully with some help) and maintain the module for at least two years. Cheers, Bastian [toml-lang]: https://github.com/toml-lang/toml [pep]: https://www.python.org/dev/peps/pep-0518 [pip]: https://github.com/pypa/pip [pipenv]: https://github.com/pypa/pipenv [toml]: https://github.com/uiri/toml [pytoml]: https://github.com/avakar/pytoml [tomlkit]: https://github.com/sdispater/tomlkit [requirements]: https://devguide.python.org/stdlibchanges/#requirements -- Dr. Bastian Venthur http://venthur.de Debian Developer venthur at debian org

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congrats on 3.5! Alas, windows 7 users are having problems installing it
by Laura Creighton 15 Sep '19

15 Sep '19

webmaster has already heard from 4 people who cannot install it. I sent them to the bug tracker or to python-list but they seem not to have gone either place. Is there some guide I should be sending them to, 'how to debug installation problems'? Laura

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python3 -bb and hash collisions
by Daniel Holth 14 Sep '19

14 Sep '19

set([u"foo", b"foo]) will error because the two kinds of string have the same hash, and this causes a comparison. Is that correct?

11 18

Snapshot formats in tracemalloc vs profiler
by Yonatan Zunger 14 Aug '19

14 Aug '19

Hi everyone, Something occurred to me while trying to analyze code today: profiler and cProfiler emit their data in pstats format, which various tools and libraries consume. tracemalloc, on the other hand, uses a completely separate format which nonetheless contains similar data. In fact, in many non-Python applications I've worked in, heap and CPU profiles were always emitted in identical formats, which allowed things like visual representations of stack traces where memory is allocated, and these have proven quite useful in practice and allowed lots of sharing of tools across many applications. Is there a particular design reason why these formats are different in Python right now? Would it make sense to consider allowing them to match, e.g. having a tracemalloc.dump_pstats() method? Yonatan

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Have a big machine and spare time? Here's a possible Python bug.
by Tim Peters 19 Jul '19

19 Jul '19

There's a Stackoverflow report[1] I suspect is worth looking into, but it requires far more RAM (over 80GB) than I have). The OP whittled it down to a reasonably brief & straightforward pure Python 3 program. It builds a ternary search tree, with perhaps a billion nodes. The problem is that it "takes forever" for Python to reclaim the tree storage when it goes out of scope (the author waited at least hours). Alas, the OP said it takes about 45 minutes to build the tree, and the problem goes away if the tree is materially smaller. So it takes a long time just to try once. With a tree about 10x smaller, for me it takes about 45 seconds for Python to reclaim the tree storage. The tree is deep enough that the "trashcan" may be implicated, and the node objects are small enough that obmalloc carves them out of a (relatively) great many arenas. Those are two ways in which Python _may_ be to blame. The sheer number of objects involved may be provoking edge cases we normally never see. But, for a start, it would be good to know if anyone else can actually reproduce the problem. [1] https://stackoverflow.com/questions/56228799/python-hangs-indefinitely-tryi…

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strip behavior provides inconsistent results with certain strings
by dan＠bauman.space 03 Jul '19

03 Jul '19

Anyone experienced anything like this? The behavior seems consistent but unexpected. python 3.6 on both windows (10) and linux (ubuntu 18.04) seem to exhibit the same odd behavior. something about a docker-image looking string seems to trigger this behavior. The behavior seems as expected for other strings. Python 3.6.5 |Anaconda, Inc.| (default, Mar 29 2018, 13:32:41) [MSC v.1900 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. sample_string_1 = "namespace/something-plugin-extra:dev" print(sample_string_1.lstrip("namespace/something-plugin")) xtra:dev print(sample_string_1.lstrip("namespace/something-plug")) xtra:dev print(sample_string_1.lstrip("namespace/something-plu")) xtra:dev print(sample_string_1.lstrip("namespace/something-pl")) ugin-extra:dev sample_string_1 = "namespace/something-plugxx-extra:dev" print(sample_string_1.lstrip("namespace/something-plugin")) xx-extra:dev print(sample_string_1.lstrip("namespace/something-plug")) xx-extra:dev print(sample_string_1.lstrip("namespace/something-plu")) xx-extra:dev print(sample_string_1.lstrip("namespace/something-pl")) ugxx-extra:dev Python 3.6.5 (default, Apr 1 2018, 05:46:30) [GCC 7.3.0] on linux Type "help", "copyright", "credits" or "license" for more information. sample_string_1 = "namespace/something-plugin-extra:dev" print(sample_string_1.lstrip("namespace/something-plugin")) xtra:dev print(sample_string_1.lstrip("namespace/something-plug")) xtra:dev print(sample_string_1.lstrip("namespace/something-plu")) xtra:dev print(sample_string_1.lstrip("namespace/something-pl")) ugin-extra:dev sample_string_1 = "namespace/something-plugxx-extra:dev" print(sample_string_1.lstrip("namespace/something-plugin")) xx-extra:dev print(sample_string_1.lstrip("namespace/something-plug")) xx-extra:dev print(sample_string_1.lstrip("namespace/something-plu")) xx-extra:dev print(sample_string_1.lstrip("namespace/something-pl")) ugxx-extra:dev

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PEP 581 has been updated with "Downsides of GitHub" section
by Mariatta 03 Jul '19

03 Jul '19

Hi, I've updated PEP 581 yesterday, adding the "Downsides of GitHub" section. https://www.python.org/dev/peps/pep-0581/#downsides-of-github Other parts of the PEP has also been updated to reflect recent changes to roundup/bpo that happened after PEP 581's acceptance, for example: - ability to automatically close issues when a PR has been merged. This was added to bpo after PEP 581's acceptance. I've also created an issue in devguide so that this can be documented: https://github.com/python/devguide/issues/502 - Availability of REST API in Roundup/bpo. REST API has been requested in Roundup for several years, and there was no activity on it since 2016. REST API has been incorporated to Roundup in February 2019, but it is not yet incorporated to bpo. - Availability of CI for Roundup/bpo. There is CI running on Roundup's unofficial GitHub mirror. But pull requests aren't happening there. Mercurial patches are still how you would contribute to it. Please re-read PEP 581 in its entirety. I plan to update PEP 588 sometime this weekend or next, to incorporate the discussions and suggestions brought up in Python Language Summit 2019:( http://pyfound.blogspot.com/2019/05/mariatta-wijaya-lets-use-github-issues.… ) Some of the items brought up during the language summit: - we're talking with The PSF to get a professional PM to handle the migration (mentioned by steering council members). - we should create a playground GitHub issue tracker and copy 100s of tickets from bpo to there (suggested by Barry Warsaw) - we should be updating devguide ahead of the actual migration, so core developers and release managers have time to review and learn the new workflow. (suggested by Ned Deily) - Devguide should have a section for "how to triage issues on GitHub" (sorry I forgot who said this, but it is in my note) - Some people liked having screencast of "how to do X on GitHub" (similar to miss-islington's Youtube demo https://www.youtube.com/watch?v=p85YtKKLNno). It would be good if we can do more of them. (suggested by Davin Potts) Thanks. ᐧ

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Python-Dev June 2019