Python-Dev March 2017

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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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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

5 6

Help requested with Python 2.7 performance regression
by Barry Warsaw 16 Aug '17

16 Aug '17

Hello all, Over in Ubuntu, we've gotten reports about some performance regressions in Python 2.7 when moving from Trusty (14.04 LTS) to Xenial (16.04 LTS). Trusty's version is based on 2.7.6 while Xenial's version is based on 2.7.12 with bits of .13 cherry picked. We've not been able to identify any change in Python itself (or the Debian/Ubuntu deltas) which could account for this, so the investigation has led to various gcc compiler options and version differences. In particular disabling LTO (link-time optimization) seems to have a positive impact, but doesn't completely regain the loss. Louis (Cc'd here) has done a ton of work to measure and analyze the problem, but we've more or less hit a roadblock, so we're taking the issue public to see if anybody on this mailing list has further ideas. A detailed analysis is available in this Google doc: https://docs.google.com/document/d/1zrV3OIRSo99fd2Ty4YdGk_scmTRDmVauBprKL8e… The document should be public for comments and editing. If you have any thoughts, or other lines of investigation you think are worthwhile pursuing, please add your comments to the document. Cheers, -Barry

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Python FTP Injections Allow for Firewall Bypass (oss-security advisory)
by nospam＠curso.re 21 Jun '17

21 Jun '17

Hello, I have just noticed that an FTP injection advisory has been made public on the oss-security list. The author says that he an exploit exists but it won't be published until the code is patched You may be already aware, but it would be good to understand what is the position of the core developers about this. The advisory is linked below (with some excerpts in this message): http://blog.blindspotsecurity.com/2017/02/advisory-javapython-ftp-injection… Protocol injection flaws like this have been an area of research of mine for the past few couple of years and as it turns out, this FTP protocol injection allows one to fool a victim's firewall into allowing TCP connections from the Internet to the vulnerable host's system on any "high" port (1024-65535). A nearly identical vulnerability exists in Python's urllib2 and urllib libraries. In the case of Java, this attack can be carried out against desktop users even if those desktop users do not have the Java browser plugin enabled. As of 2017-02-20, the vulnerabilities discussed here have not been patched by the associated vendors, despite advance warning and ample time to do so. [...] Python's built-in URL fetching library (urllib2 in Python 2 and urllib in Python 3) is vulnerable to a nearly identical protocol stream injection, but this injection appears to be limited to attacks via directory names specified in the URL. [...] The Python security team was notified in January 2016. Information provided included an outline of the possibility of FTP/firewall attacks. Despite repeated follow-ups, there has been no apparent action on their part. Best regards, -- Stefano P.S. I am posting from gmane, I hope that this is OK.

9 9

Issue #21071: change struct.Struct.format type from bytes to str
by Victor Stinner 16 Jun '17

16 Jun '17

Hi I would like to change struct.Struct.format type from bytes to str. I don't expect that anyone uses this attribute, and struct.Struct() constructor accepts both bytes and str. http://bugs.python.org/issue21071 It's just to be convenient: more functions accept str than bytes in Python 3. Example: print() (python3 -bb raises an exceptions if you pass bytes to print). Is anything opposed to breaking the backward compatibility? Victor

3 3

PEP 545: Python Documentation Translations
by Julien Palard 21 May '17

21 May '17

Hi. Here's PEP 545, ready to be reviewed! This is the follow-up to the "PEP: Python Documentation Translations" thread on python-ideas [1]_, itself a follow-up of the "Translated Python documentation" thread on python-dev [2]_. This PEP describes the steps to make existing and future translations of the Python documentation official and accessible on docs.python.org. You can read it rendered here https://www.python.org/dev/peps/pep-0545/ or inline here, I'll happily get your feedback. ======================================== PEP: 545 Title: Python Documentation Translations Version: $Revision$ Last-Modified: $Date$ Author: Victor Stinner <victor.stinner(a)gmail.com>, Inada Naoki <songofacandy(a)gmail.com>, Julien Palard <julien(a)palard.fr> Status: Draft Type: Process Content-Type: text/x-rst Created: 04-Mar-2017 Abstract ======== The intent of this PEP is to make existing translations of the Python Documentation more accessible and discoverable. By doing so, we hope to attract and motivate new translators and new translations. Translated documentation will be hosted on python.org. Examples of two active translation teams: * http://docs.python.org/fr/: French * http://docs.python.org/ja/: Japanese http://docs.python.org/en/ will redirect to http://docs.python.org/. Sources of translated documentation will be hosted in the Python organization on GitHub: https://github.com/python/. Contributors will have to sign the Python Contributor Agreement (CLA) and the license will be the PSF License. Motivation ========== On the French ``#python-fr`` IRC channel on freenode, it's not rare to meet people who don't speak English and so are unable to read the Python official documentation. Python wants to be widely available to all users in any language: this is also why Python 3 supports any non-ASCII identifiers: https://www.python.org/dev/peps/pep-3131/#rationale There are a least 3 groups of people who are translating the Python documentation to their native language (French [16]_ [17]_ [18]_, Japanese [19]_ [20]_, Spanish [21]_) even though their translations are not visible on d.p.o. Other, less visible and less organized groups, are also translating the documentation, we've heard of Russian [26]_, Chinese and Korean. Others we haven't found yet might also exist. This PEP defines rules describing how to move translations on docs.python.org so they can easily be found by developers, newcomers and potential translators. The Japanese team has (as of March 2017) translated ~80% of the documentation, the French team ~20%. French translation went from 6% to 23% in 2016 [13]_ with 7 contributors [14]_, proving a translation team can be faster than the rate the documentation mutates. Quoting Xiang Zhang about Chinese translations: I have seen several groups trying to translate part of our official doc. But their efforts are disperse and quickly become lost because they are not organized to work towards a single common result and their results are hold anywhere on the Web and hard to find. An official one could help ease the pain. Rationale ========= Translation ----------- Issue tracker ''''''''''''' Considering that issues opened about translations may be written in the translation language, which can be considered noise but at least is inconsistent, issues should be placed outside `bugs.python.org <https://bugs.python.org/>`_ (b.p.o). As all translation must have their own github project (see `Repository for Po Files`_), they must use the associated github issue tracker. Considering the noise induced by translation issues redacted in any languages which may beyond every warnings land in b.p.o, triage will have to be done. Considering that translations already exist and are not actually a source of noise in b.p.o, an unmanageable amount of work is not to be expected. Considering that Xiang Zhang and Victor Stinner are already triaging, and Julien Palard is willing to help on this task, noise on b.p.o is not to be expected. Also, language team coordinators (see `Language Team`_) should help with triaging b.p.o by properly indicating, in the language of the issue author if required, the right issue tracker. Branches '''''''' Translation teams should focus on last stable versions, and use tools (scripts, translation memory, …) to automatically translate what is done in one branch to other branches. .. note:: Translation memories are a kind of database of previously translated paragraphs, even removed ones. See also `Sphinx Internationalization <http://www.sphinx-doc.org/en/stable/intl.html>`_. The three currently stable branches that will be translated are [12]_: 2.7, 3.5, and 3.6. The scripts to build the documentation of older branches needs to be modified to support translation [12]_, whereas these branches now only accept security-only fixes. The development branch (master) should have a lower translation priority than stable branches. But docsbuild-scripts should build it anyway so it is possible for a team to work on it to be ready for the next release. Hosting ------- Domain Name, Content negotiation and URL '''''''''''''''''''''''''''''''''''''''' Different translations can be identified by changing one of the following: Country Code Top Level Domain (CCTLD), path segment, subdomain or content negotiation. Buying a CCTLD for each translations is expensive, time-consuming, and sometimes almost impossible when already registered, this solution should be avoided. Using subdomains like "es.docs.python.org" or "docs.es.python.org" is possible but confusing ("is it `es.docs.python.org` or `docs.es.python.org`?"). Hyphens in subdomains like `pt-br.doc.python.org` is uncommon and SEOMoz [23]_ correlated the presence of hyphens as a negative factor. Usage of underscores in subdomain is prohibited by the RFC1123 [24]_, section 2.1. Finally, using subdomains means creating TLS certificates for each language. This not only requires more maintenance but will also cause issues in language switcher if, as for version switcher, we want a preflight to check if the translation exists in the given version: preflight will probably be blocked by same-origin-policy. Wildcard TLS certificates are very expensive. Using content negotiation (HTTP headers ``Accept-Language`` in the request and ``Vary: Accept-Language``) leads to a bad user experience where they can't easily change the language. According to Mozilla: "This header is a hint to be used when the server has no way of determining the language via another way, like a specific URL, that is controlled by an explicit user decision." [25]_. As we want to be able to easily change the language, we should not use the content negotiation as a main language determination, so we need something else. Last solution is to use the URL path, which looks readable, allows for an easy switch from a language to another, and nicely accepts hyphens. Typically something like: "docs.python.org/de/" or, by using a hyphen: "docs.python.org/pt-BR/". As for the version, sphinx-doc does not support compiling for multiple languages, so we'll have full builds rooted under a path, exactly like we're already doing with versions. So we can have "docs.python.org/de/3.6/" or "docs.python.org/3.6/de/". A question that arises is: "Does the language contain multiple versions or does the version contain multiple languages?". As versions exist in any case and translations for a given version may or may not exist, we may prefer "docs.python.org/3.6/de/", but doing so scatters languages everywhere. Having "/de/3.6/" is clearer, meaning: "everything under /de/ is written in German". Having the version at the end is also a habit taken by readers of the documentation: they like to easily change the version by changing the end of the path. So we should use the following pattern: "docs.python.org/LANGUAGE_TAG/VERSION/". The current documentation is not moved to "/en/", insted "docs.python.org/en/" will redirect to "docs.python.org". Language Tag '''''''''''' A common notation for language tags is the IETF Language Tag [3]_ [4]_ based on ISO 639, although gettext uses ISO 639 tags with underscores (ex: ``pt_BR``) instead of dashes to join tags [5]_ (ex: ``pt-BR``). Examples of IETF Language Tags: ``fr`` (French), ``ja`` (Japanese), ``pt-BR`` (Orthographic formulation of 1943 - Official in Brazil). It is more common to see dashes instead of underscores in URLs [6]_, so we should use IETF language tags, even if sphinx uses gettext internally: URLs are not meant to leak the underlying implementation. It's uncommon to see capitalized letters in URLs, and docs.python.org doesn't use any, so it may hurt readability by attracting the eye on it, like in: "https://docs.python.org/pt-BR/3.6/library/stdtypes.html". RFC 5646 (Tags for Identifying Languages (IETF)) section-2.1 [7]_ states that tags are not case sensitive. As the RFC allows lower case, and it enhances readability, we should use lowercased tags like ``pt-br``. It's redundant to display both language and country code if they're the same, for example: "de-DE" or "fr-FR". Although it might make sense, respectively meaning "German as spoken in Germany" and "French as spoken in France", it's not useful information for the reader. So we may drop these redundancies and only keep the country code for cases where it makes sense, for example, "pt-BR" for "Portuguese as spoken in Brazil". So we should use IETF language tags, lowercased, like ``/fr/``, ``/pt-br/``, ``/de/`` and so on. Fetching And Building Translations '''''''''''''''''''''''''''''''''' Currently docsbuild-scripts are building the documentation [8]_. These scripts should be modified to fetch and build translations. Building new translations is like building new versions so, while we're adding complexity it is not that much. Two steps should be configurable distinctively: Building a new language, and adding it to the language switcher. This allows a transition step between "we accepted the language" and "it is translated enough to be made public". During this step, translators can review their modifications on d.p.o without having to build the documentation locally. From the translation repositories, only the ``.po`` files should be opened by the docsbuild-script to keep the attack surface and probable bug sources at a minimum. This means no translation can patch sphinx to advertise their translation tool. (This specific feature should be handled by sphinx anyway [9]_). Community --------- Mailing List '''''''''''' The `doc-sig`_ mailing list will be used to discuss cross-language changes on translated documentation. There is also the i18n-sig list but it's more oriented towards i18n APIs [1]_ than translating the Python documentation. .. _i18n-sig: https://mail.python.org/mailman/listinfo/i18n-sig .. _doc-sig: https://mail.python.org/mailman/listinfo/doc-sig Chat '''' Due to the Python community being highly active on IRC, we should create a new IRC channel on freenode, typically #python-doc for consistency with the mailing list name. Each language coordinator can organize their own team, even by choosing another chat system if the local usage asks for it. As local teams will write in their native languages, we don't want each team in a single channel. It's also natural for the local teams to reuse their local channels like "#python-fr" for French translators. Repository for PO Files ''''''''''''''''''''''' Considering that each translation team may want to use different translation tools, and that those tools should easily be synchronized with git, all translations should expose their ``.po`` files via a git repository. Considering that each translation will be exposed via git repositories, and that Python has migrated to GitHub, translations will be hosted on github. For consistency and discoverability, all translations should be in the same github organization and named according to a common pattern. Given that we want translations to be official, and that Python already has a github organization, translations should be hosted as projects of the `Python GitHub organization`_. For consistency, translation repositories should be called ``python-docs-LANGUAGE_TAG`` [22]_, using the language tag used in paths: without region subtag if redundent, and lowercased. The docsbuild-scripts may enforce this rule by refusing to fetch outside of the Python organization or a wrongly named repository. The CLA bot may be used on the translation repositories, but with a limited effect as local coordinators may synchronize themselves with translations from an external tool, like transifex, and loose track of who translated what in the process. Versions can be hosted on different repositories, different directories or different branches. Storing them on different repositories will probably pollute the Python github organization. As it is typical and natural to use branches to separate versions, branches should be used to do so. .. _Python GitHub organization: https://github.com/python/ Translation tools ''''''''''''''''' Most of the translation work is actually done on Transifex [15]_. Other tools may be used later https://pontoon.mozilla.org/ and http://zanata.org/ Contributor Agreement ''''''''''''''''''''' Contributions to translated documentation will be requested to sign the Python Contributor Agreement (CLA): https://www.python.org/psf/contrib/contrib-form/ Language Team ''''''''''''' Each language team should have one coordinator responsible for: - Managing the team. - Choosing and managing the tools the team will use (chat, mailing list, …). - Ensure contributors understand and agree with the CLA. - Ensure quality (grammar, vocabulary, consistency, filtering spam, ads, …). - Redirect issues posted on b.p.o to the correct GitHub issue tracker for the language. The license will be the `PSF License <https://docs.python.org/3/license.html>`_, and copyright should be transferable to PSF later. Alternatives ------------ Simplified English '''''''''''''''''' It would be possible to introduce a "simplified English" version like wikipedia did [10]_, as discussed on python-dev [11]_, targeting English learners and children. Pros: It yields a single translation, theoretically readable by everyone and reviewable by current maintainers. Cons: Subtle details may be lost, and translators from English to English may be hard to find as stated by Wikipedia: > The main English Wikipedia has 5 million articles, written by nearly 140K active users; the Swedish Wikipedia is almost as big, 3M articles from only 3K active users; but the Simple English Wikipedia has just 123K articles and 871 active users. That's fewer articles than Esperanto! Changes ======= Migrate GitHub Repositories --------------------------- We (authors of this PEP) already own French and Japanese Git repositories, so moving them to the Python documentation organization will not be a problem. We'll however be following the `New Translation Procedure`_. Patch docsbuild-scripts to Compile Translations ----------------------------------------------- Docsbuild-script must be patched to: - List the language tags to build along with the branches to build. - List the language tags to display in the language switcher. - Find translation repositories by formatting ``github.com:python/python-docs-{language_tag}.git`` (See `Repository for Po Files`_) - Build translations for each branch and each language. Patched docsbuild-scripts must only open ``.po`` files from translation repositories. List coordinators in the devguide --------------------------------- Add a page or a section with an empty list of coordinators to the devguide, each new coordinator will be added to this list. Create sphinx-doc Language Switcher ----------------------------------- Highly similar to the version switcher, a language switcher must be implemented. This language switcher must be configurable to hide or show a given language. The language switcher will only have to update or add the language segment to the path like the current version switcher does. Unlike the version switcher, no preflight are required as destination page always exists (translations does not add or remove pages). Untranslated (but existing) pages still exists, they should however be rendered as so, see `Enhance Rendering of Untranslated and Fuzzy Translations`_. Update sphinx-doc Version Switcher ---------------------------------- The ``patch_url`` function of the version switcher in ``version_switch.js`` have to be updated to understand and allow the presence of the language segment in the path. Enhance Rendering of Untranslated and Fuzzy Translations -------------------------------------------------------- It's an opened sphinx issue [9]_, but we'll need it so we'll have to work on it. Translated, fuzzy, and untranslated paragraphs should be differentiated. (Fuzzy paragraphs have to warn the reader what he's reading may be out of date.) New Translation Procedure ========================= Designate a Coordinator ----------------------- The first step is to designate a coordinator, see `Language Team`_, The coordinator must sign the CLA. The coordinator should be added to the list of translation coordinators on the devguide. Create Github Repository ------------------------ Create a repository named "python-docs-{LANGUAGE_TAG}" (IETF language tag, without redundent region subtag, with a dash, and lowercased.) on the Python github organization (See `Repository For Po Files`_.), and grant the language coordinator push rights to this repository. Add support for translations in docsbuild-scripts ------------------------------------------------- As soon as the translation hits its first commits, update the docsbuild-scripts configuration to build the translation (but not displaying it in the language switcher). Add Translation to the Language Switcher ---------------------------------------- As soon as the translation hits: - 100% of bugs.html with proper links to the language repository issue tracker. - 100% of tutorial. - 100% of library/functions (builtins). the translation can be added to the language switcher. Previous Discussions ==================== - `[Python-ideas] Cross link documentation translations (January, 2016)`_ - `[Python-ideas] Cross link documentation translations (January, 2016)`_ - `[Python-ideas] https://docs.python.org/fr/ ? (March 2016)`_ .. _[Python-ideas] Cross link documentation translations (January, 2016): https://mail.python.org/pipermail/python-ideas/2016-January/038010.html .. _[Python-Dev] Translated Python documentation (Febrary 2016): https://mail.python.org/pipermail/python-dev/2017-February/147416.html .. _[Python-ideas] https://docs.python.org/fr/ ? (March 2016): https://mail.python.org/pipermail/python-ideas/2016-March/038879.html References ========== .. [1] [I18n-sig] Hello Python members, Do you have any idea about Python documents? (https://mail.python.org/pipermail/i18n-sig/2013-September/002130.html) .. [2] [Doc-SIG] Localization of Python docs (https://mail.python.org/pipermail/doc-sig/2013-September/003948.html) .. [3] Tags for Identifying Languages (http://tools.ietf.org/html/rfc5646) .. [4] IETF language tag (https://en.wikipedia.org/wiki/IETF_language_tag) .. [5] GNU Gettext manual, section 2.3.1: Locale Names (https://www.gnu.org/software/gettext/manual/html_node/Locale-Names.html) .. [6] Semantic URL: Slug (https://en.wikipedia.org/wiki/Semantic_URL#Slug) .. [7] Tags for Identifying Languages: Formatting of Language Tags (https://tools.ietf.org/html/rfc5646#section-2.1.1) .. [8] Docsbuild-scripts github repository (https://github.com/python/docsbuild-scripts/) .. [9] i18n: Highlight untranslated paragraphs (https://github.com/sphinx-doc/sphinx/issues/1246) .. [10] Wikipedia: Simple English (https://simple.wikipedia.org/wiki/Main_Page) .. [11] Python-dev discussion about simplified english (https://mail.python.org/pipermail/python-dev/2017-February/147446.html) .. [12] Passing options to sphinx from Doc/Makefile (https://github.com/python/cpython/commit/57acb82d275ace9d9d854b156611e641f6…) .. [13] French translation progression (https://mdk.fr/pycon2016/#/11) .. [14] French translation contributors (https://github.com/AFPy/python_doc_fr/graphs/contributors?from=2016-01-01&t…) .. [15] Python-doc on Transifex (https://www.transifex.com/python-doc/) .. [16] French translation (https://www.afpy.org/doc/python/) .. [17] French translation github (https://github.com/AFPy/python_doc_fr) .. [18] French mailing list (http://lists.afpy.org/mailman/listinfo/traductions) .. [19] Japanese translation (http://docs.python.jp/3/) .. [20] Japanese github (https://github.com/python-doc-ja/python-doc-ja) .. [21] Spanish translation (http://docs.python.org.ar/tutorial/3/index.html) .. [22] [Python-Dev] Translated Python documentation: doc vs docs (https://mail.python.org/pipermail/python-dev/2017-February/147472.html) .. [23] Domains - SEO Best Practices | Moz (https://moz.com/learn/seo/domain) .. [24] Requirements for Internet Hosts -- Application and Support (https://www.ietf.org/rfc/rfc1123.txt) .. [25] Accept-Language (https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language) .. [26] Документация Python 2.7! (http://python-lab.ru/documentation/index.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 coding: utf-8 End: ======================================== .. [1] [Python-ideas] PEP: Python Documentation Translations (https://mail.python.org/pipermail/python-ideas/2017-March/045226.html) .. [2] [Python-Dev] Translated Python documentation (https://mail.python.org/pipermail/python-dev/2017-February/147416.html) Bests, -- Julien Palard https://mdk.fr

6 11

PEP 538: Coercing the legacy C locale to a UTF-8 based locale
by Nick Coghlan 09 May '17

09 May '17

Hi folks, Late last year I started working on a change to the CPython CLI (*not* the shared library) to get it to coerce the legacy C locale to something based on UTF-8 when a suitable locale is available. After a couple of rounds of iteration on linux-sig and python-ideas, I'm now bringing it to python-dev as a concrete proposal for Python 3.7. For most folks, reading the Abstract plus the draft docs updates in the reference implementation will tell you everything you need to know (if the C.UTF-8, C.utf8 or UTF-8 locales are available, the CLI will automatically attempt to coerce the legacy C locale to one of those rather than persisting with the latter's default assumption of ASCII as the preferred text encoding). However, the full PEP goes into a lot more detail on: * exactly what's broken about CPython's behaviour in the legacy C locale * why I'm in favour of this particular approach to fixing it (i.e. it integrates better with other C/C++ components, as well as being amenable to redistributor backports for 3.6, and environment based configuration for 3.5 and earlier) * why I think implementing both this change *and* Victor's more comprehensive "PYTHONUTF8 mode" proposal in PEP 540 will be better than implementing just one or the other (in some situations, ignoring the platform locale subsystem entirely really is the right approach, and that's the aspect PEP 540 tackles, while this PEP tackles the situations where the C locale behaviour is broken, but you still need to be consistent with the platform settings). Cheers, Nick. ================================== PEP: 538 Title: Coercing the legacy C locale to a UTF-8 based locale Version: $Revision$ Last-Modified: $Date$ Author: Nick Coghlan <ncoghlan(a)gmail.com> Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 28-Dec-2016 Python-Version: 3.7 Post-History: 03-Jan-2017 (linux-sig), 07-Jan-2017 (python-ideas), 05-Mar-2017 (python-dev) Abstract ======== An ongoing challenge with Python 3 on \*nix systems is the conflict between needing to use the configured locale encoding by default for consistency with other C/C++ components in the same process and those invoked in subprocesses, and the fact that the standard C locale (as defined in POSIX:2001) typically implies a default text encoding of ASCII, which is entirely inadequate for the development of networked services and client applications in a multilingual world. PEP 540 proposes a change to CPython's handling of the legacy C locale such that CPython will assume the use of UTF-8 in such environments, rather than persisting with the demonstrably problematic assumption of ASCII as an appropriate encoding for communicating with operating system interfaces. This is a good approach for cases where network encoding interoperability is a more important concern than local encoding interoperability. However, it comes at the cost of making CPython's encoding assumptions diverge from those of other C and C++ components in the same process, as well as those of components running in subprocesses that share the same environment. It also requires changes to the internals of how CPython itself works, rather than using existing configuration settings that are supported by Python versions prior to Python 3.7. Accordingly, this PEP proposes that independently of the UTF-8 mode proposed in PEP 540, the way the CPython implementation handles the default C locale be changed such that: * unless the new ``PYTHONCOERCECLOCALE`` environment variable is set to ``0``, the standalone CPython binary will automatically attempt to coerce the ``C`` locale to the first available locale out of ``C.UTF-8``, ``C.utf8``, or ``UTF-8`` * if the locale is successfully coerced, and PEP 540 is not accepted, then ``PYTHONIOENCODING`` (if not otherwise set) will be set to ``utf-8:surrogateescape``. * if the locale is successfully coerced, and PEP 540 *is* accepted, then ``PYTHONUTF8`` (if not otherwise set) will be set to ``1`` * if the subsequent runtime initialization process detects that the legacy ``C`` locale remains active (e.g. none of ``C.UTF-8``, ``C.utf8`` or ``UTF-8`` are available, locale coercion is disabled, or the runtime is embedded in an application other than the main CPython binary), and the ``PYTHONUTF8`` feature defined in PEP 540 is also disabled (or not implemented), it will emit a warning on stderr that use of the legacy ``C`` locale's default ASCII text encoding may cause various Unicode compatibility issues With this change, any \*nix platform that does *not* offer at least one of the ``C.UTF-8``, ``C.utf8`` or ``UTF-8`` locales as part of its standard configuration would only be considered a fully supported platform for CPython 3.7+ deployments when either the new ``PYTHONUTF8`` mode defined in PEP 540 is used, or else a suitable locale other than the default ``C`` locale is configured explicitly (e.g. `en_AU.UTF-8`, ``zh_CN.gb18030``). Redistributors (such as Linux distributions) with a narrower target audience than the upstream CPython development team may also choose to opt in to this locale coercion behaviour for the Python 3.6.x series by applying the necessary changes as a downstream patch when first introducing Python 3.6.0. Background ========== While the CPython interpreter is starting up, it may need to convert from the ``char *`` format to the ``wchar_t *`` format, or from one of those formats to ``PyUnicodeObject *``, in a way that's consistent with the locale settings of the overall system. It handles these cases by relying on the operating system to do the conversion and then ensuring that the text encoding name reported by ``sys.getfilesystemencoding()`` matches the encoding used during this early bootstrapping process. On Apple platforms (including both Mac OS X and iOS), this is straightforward, as Apple guarantees that these operations will always use UTF-8 to do the conversion. On Windows, the limitations of the ``mbcs`` format used by default in these conversions proved sufficiently problematic that PEP 528 and PEP 529 were implemented to bypass the operating system supplied interfaces for binary data handling and force the use of UTF-8 instead. On Android, many components, including CPython, already assume the use of UTF-8 as the system encoding, regardless of the locale setting. However, this isn't the case for all components, and the discrepancy can cause problems in some situations (for example, when using the GNU readline module [16_]). On non-Apple and non-Android \*nix systems, these operations are handled using the C locale system in glibc, which has the following characteristics [4_]: * by default, all processes start in the ``C`` locale, which uses ``ASCII`` for these conversions. This is almost never what anyone doing multilingual text processing actually wants (including CPython and C/C++ GUI frameworks). * calling ``setlocale(LC_ALL, "")`` reconfigures the active locale based on the locale categories configured in the current process environment * if the locale requested by the current environment is unknown, or no specific locale is configured, then the default ``C`` locale will remain active The specific locale category that covers the APIs that CPython depends on is ``LC_CTYPE``, which applies to "classification and conversion of characters, and to multibyte and wide characters" [5_]. Accordingly, CPython includes the following key calls to ``setlocale``: * in the main ``python`` binary, CPython calls ``setlocale(LC_ALL, "")`` to configure the entire C locale subsystem according to the process environment. It does this prior to making any calls into the shared CPython library * in ``Py_Initialize``, CPython calls ``setlocale(LC_CTYPE, "")``, such that the configured locale settings for that category *always* match those set in the environment. It does this unconditionally, and it *doesn't* revert the process state change in ``Py_Finalize`` (This summary of the locale handling omits several technical details related to exactly where and when the text encoding declared as part of the locale settings is used - see PEP 540 for further discussion, as these particular details matter more when decoupling CPython from the declared C locale than they do when overriding the locale with one based on UTF-8) These calls are usually sufficient to provide sensible behaviour, but they can still fail in the following cases: * SSH environment forwarding means that SSH clients may sometimes forward client locale settings to servers that don't have that locale installed. This leads to CPython running in the default ASCII-based C locale * some process environments (such as Linux containers) may not have any explicit locale configured at all. As with unknown locales, this leads to CPython running in the default ASCII-based C locale The simplest way to deal with this problem for currently released versions of CPython is to explicitly set a more sensible locale when launching the application. For example:: LC_ALL=C.UTF-8 LANG=C.UTF-8 python3 ... The ``C.UTF-8`` locale is a full locale definition that uses ``UTF-8`` for the ``LC_CTYPE`` category, and the same settings as the ``C`` locale for all other categories (including ``LC_COLLATE``). It is offered by a number of Linux distributions (including Debian, Ubuntu, Fedora, Alpine and Android) as an alternative to the ASCII-based C locale. Mac OS X and other \*BSD systems have taken a different approach, and instead of offering a ``C.UTF-8`` locale, instead offer a partial ``UTF-8`` locale that only defines the ``LC_CTYPE`` category. On such systems, the preferred environmental locale adjustment is to set ``LC_CTYPE=UTF-8`` rather than to set ``LC_ALL`` or ``LANG``. [17_] In the specific case of Docker containers and similar technologies, the appropriate locale setting can be specified directly in the container image definition. Another common failure case is developers specifying ``LANG=C`` in order to see otherwise translated user interface messages in English, rather than the more narrowly scoped ``LC_MESSAGES=C``. Relationship with other PEPs ============================ This PEP shares a common problem statement with PEP 540 (improving Python 3's behaviour in the default C locale), but diverges markedly in the proposed solution: * PEP 540 proposes to entirely decouple CPython's default text encoding from the C locale system in that case, allowing text handling inconsistencies to arise between CPython and other C/C++ components running in the same process and in subprocesses. This approach aims to make CPython behave less like a locale-aware C/C++ application, and more like C/C++ independent language runtimes like the JVM, .NET CLR, Go, Node.js, and Rust * this PEP proposes to override the legacy C locale with a more recently defined locale that uses UTF-8 as its default text encoding. This means that the text encoding override will apply not only to CPython, but also to any locale aware extension modules loaded into the current process, as well as to locale aware C/C++ applications invoked in subprocesses that inherit their environment from the parent process. This approach aims to retain CPython's traditional strong support for integration with other components written in C and C++, while actively helping to push forward the adoption and standardisation of the C.UTF-8 locale as a Unicode-aware replacement for the legacy C locale in the wider C/C++ ecosystem After reviewing both PEPs, it became clear that they didn't actually conflict at a technical level, and the proposal in PEP 540 offered a superior option in cases where no suitable locale was available, as well as offering a better reference behaviour for platforms where the notion of a "locale encoding" doesn't make sense (for example, embedded systems running MicroPython rather than the CPython reference interpreter). Meanwhile, this PEP offered improved compatibility with other C/C++ components, and an approach more amenable to being backported to Python 3.6 by downstream redistributors. As a result, this PEP was amended to refer to PEP 540 as a complementary solution that offered improved behaviour both when locale coercion triggered, as well as when none of the standard UTF-8 based locales were available. The availability of PEP 540 also meant that the ``LC_CTYPE=en_US.UTF-8`` legacy fallback was removed from the list of UTF-8 locales tried as a coercion target, with CPython instead relying solely on the proposed PYTHONUTF8 mode in such cases. Motivation ========== While Linux container technologies like Docker, Kubernetes, and OpenShift are best known for their use in web service development, the related container formats and execution models are also being adopted for Linux command line application development. Technologies like Gnome Flatpak [7_] and Ubunty Snappy [8_] further aim to bring these same techniques to Linux GUI application development. When using Python 3 for application development in these contexts, it isn't uncommon to see text encoding related errors akin to the following:: $ docker run --rm fedora:25 python3 -c 'print("ℙƴ☂ℌøἤ")' Unable to decode the command from the command line: UnicodeEncodeError: 'utf-8' codec can't encode character '\udce2' in position 7: surrogates not allowed $ docker run --rm ncoghlan/debian-python python3 -c 'print("ℙƴ☂ℌøἤ")' Unable to decode the command from the command line: UnicodeEncodeError: 'utf-8' codec can't encode character '\udce2' in position 7: surrogates not allowed Even though the same command is likely to work fine when run locally:: $ python3 -c 'print("ℙƴ☂ℌøἤ")' ℙƴ☂ℌøἤ The source of the problem can be seen by instead running the ``locale`` command in the three environments:: $ locale | grep -E 'LC_ALL|LC_CTYPE|LANG' LANG=en_AU.UTF-8 LC_CTYPE="en_AU.UTF-8" LC_ALL= $ docker run --rm fedora:25 locale | grep -E 'LC_ALL|LC_CTYPE|LANG' LANG= LC_CTYPE="POSIX" LC_ALL= $ docker run --rm ncoghlan/debian-python locale | grep -E 'LC_ALL|LC_CTYPE|LANG' LANG= LANGUAGE= LC_CTYPE="POSIX" LC_ALL= In this particular example, we can see that the host system locale is set to "en_AU.UTF-8", so CPython uses UTF-8 as the default text encoding. By contrast, the base Docker images for Fedora and Debian don't have any specific locale set, so they use the POSIX locale by default, which is an alias for the ASCII-based default C locale. The simplest way to get Python 3 (regardless of the exact version) to behave sensibly in Fedora and Debian based containers is to run it in the ``C.UTF-8`` locale that both distros provide:: $ docker run --rm -e LANG=C.UTF-8 fedora:25 python3 -c 'print("ℙƴ☂ℌøἤ")' ℙƴ☂ℌøἤ $ docker run --rm -e LANG=C.UTF-8 ncoghlan/debian-python python3 -c 'print("ℙƴ☂ℌøἤ")' ℙƴ☂ℌøἤ $ docker run --rm -e LANG=C.UTF-8 fedora:25 locale | grep -E 'LC_ALL|LC_CTYPE|LANG' LANG=C.UTF-8 LC_CTYPE="C.UTF-8" LC_ALL= $ docker run --rm -e LANG=C.UTF-8 ncoghlan/debian-python locale | grep -E 'LC_ALL|LC_CTYPE|LANG' LANG=C.UTF-8 LANGUAGE= LC_CTYPE="C.UTF-8" LC_ALL= The Alpine Linux based Python images provided by Docker, Inc, already use the C.UTF-8 locale by default:: $ docker run --rm python:3 python3 -c 'print("ℙƴ☂ℌøἤ")' ℙƴ☂ℌøἤ $ docker run --rm python:3 locale | grep -E 'LC_ALL|LC_CTYPE|LANG' LANG=C.UTF-8 LANGUAGE= LC_CTYPE="C.UTF-8" LC_ALL= Similarly, for custom container images (i.e. those adding additional content on top of a base distro image), a more suitable locale can be set in the image definition so everything just works by default. However, it would provide a much nicer and more consistent user experience if CPython were able to just deal with this problem automatically rather than relying on redistributors or end users to handle it through system configuration changes. While the glibc developers are working towards making the C.UTF-8 locale universally available for use by glibc based applications like CPython [6_], this unfortunately doesn't help on platforms that ship older versions of glibc without that feature, and also don't provide C.UTF-8 as an on-disk locale the way Debian and Fedora do. For these platforms, the mechanism proposed in PEP 540 at least allows CPython itself to behave sensibly, albeit without any mechanism to get other C/C++ components that decode binary streams as text to do the same. Design Principles ================= The above motivation leads to the following core design principles for the proposed solution: * if a locale other than the default C locale is explicitly configured, we'll continue to respect it * if we're changing the locale setting without an explicit config option, we'll emit a warning on stderr that we're doing so rather than silently changing the process configuration. This will alert application and system integrators to the change, even if they don't closely follow the PEP process or Python release announcements. However, to minimize the chance of introducing new problems for end users, we'll do this *without* using the warnings system, so even running with ``-Werror`` won't turn it into a runtime exception * any changes made will use *existing* configuration options To minimize the negative impact on systems currently correctly configured to use GB-18030 or another partially ASCII compatible universal encoding leads to an additional design principle: * if a UTF-8 based Linux container is run on a host that is explicitly configured to use a non-UTF-8 encoding, and tries to exchange locally encoded data with that host rather than exchanging explicitly UTF-8 encoded data, CPython will endeavour to correctly round-trip host provided data that is concatenated or split solely at common ASCII compatible code points, but may otherwise emit nonsensical results. Specification ============= To better handle the cases where CPython would otherwise end up attempting to operate in the ``C`` locale, this PEP proposes that CPython automatically attempt to coerce the legacy ``C`` locale to a UTF-8 based locale when it is run as a standalone command line application. It further proposes to emit a warning on stderr if the legacy ``C`` locale is in effect at the point where the language runtime itself is initialized, and the PEP 540 UTF-8 encoding override is also disabled, in order to warn system and application integrators that they're running CPython in an unsupported configuration. Legacy C locale coercion in the standalone Python interpreter binary -------------------------------------------------------------------- When run as a standalone application, CPython has the opportunity to reconfigure the C locale before any locale dependent operations are executed in the process. This means that it can change the locale settings not only for the CPython runtime, but also for any other C/C++ components running in the current process (e.g. as part of extension modules), as well as in subprocesses that inherit their environment from the current process. After calling ``setlocale(LC_ALL, "")`` to initialize the locale settings in the current process, the main interpreter binary will be updated to include the following call:: const char *ctype_loc = setlocale(LC_CTYPE, NULL); This cryptic invocation is the API that C provides to query the current locale setting without changing it. Given that query, it is possible to check for exactly the ``C`` locale with ``strcmp``:: ctype_loc != NULL && strcmp(ctype_loc, "C") == 0 # true only in the C locale This call also returns ``"C"`` when either no particular locale is set, or the nominal locale is set to an alias for the ``C`` locale (such as ``POSIX``). Given this information, CPython can then attempt to coerce the locale to one that uses UTF-8 rather than ASCII as the default encoding. Three such locales will be tried: * ``C.UTF-8`` (available at least in Debian, Ubuntu, and Fedora 25+, and expected to be available by default in a future version of glibc) * ``C.utf8`` (available at least in HP-UX) * ``UTF-8`` (available in at least some \*BSD variants) For ``C.UTF-8`` and ``C.utf8``, the coercion will be implemented by actually setting the ``LANG`` and ``LC_ALL`` environment variables to the candidate locale name, such that future calls to ``setlocale()`` will see them, as will other components looking for those settings (such as GUI development frameworks). For the platforms where it is defined, ``UTF-8`` is a partial locale that only defines the ``LC_CTYPE`` category. Accordingly, only the ``LC_CTYPE`` environment variable would be set when using this fallback option. To adjust automatically to future changes in locale availability, these checks will be implemented at runtime on all platforms other than Mac OS X and Windows, rather than attempting to determine which locales to try at compile time. If the locale settings are changed successfully, and the ``PYTHONIOENCODING`` environment variable is currently unset, then it will be forced to ``PYTHONIOENCODING=utf-8:surrogateescape``. When this locale coercion is activated, the following warning will be printed on stderr, with the warning containing whichever locale was successfully configured:: Python detected LC_CTYPE=C, LC_ALL & LANG set to C.UTF-8 (set another locale or PYTHONCOERCECLOCALE=0 to disable this locale coercion behaviour). When falling back to the ``UTF-8`` locale, the message would be slightly different:: Python detected LC_CTYPE=C, LC_CTYPE set to UTF-8 (set another locale or PYTHONCOERCECLOCALE=0 to disable this locale coercion behaviour). In combination with PEP 540, this locale coercion will mean that the standard Python binary *and* locale aware C/C++ extensions should once again "just work" in the three main failure cases we're aware of (missing locale settings, SSH forwarding of unknown locales, and developers explicitly requesting ``LANG=C``), as long as the target platform provides at least one of the candidate UTF-8 based environments. If ``PYTHONCOERCECLOCALE=0`` is set, or none of the candidate locales is successfully configured, then initialization will continue as usual in the C locale and the Unicode compatibility warning described in the next section will be emitted just as it would for any other application. The interpreter will always check for the ``PYTHONCOERCECLOCALE`` environment variable (even when running under the ``-E`` or ``-I`` switches), as the locale coercion check necessarily takes place before any command line argument processing. Changes to the runtime initialization process --------------------------------------------- By the time that ``Py_Initialize`` is called, arbitrary locale-dependent operations may have taken place in the current process. This means that by the time it is called, it is *too late* to switch to a different locale - doing so would introduce inconsistencies in decoded text, even in the context of the standalone Python interpreter binary. Accordingly, when ``Py_Initialize`` is called and CPython detects that the configured locale is still the default ``C`` locale *and* the ``PYTHONUTF8`` feature from PEP 540 is disabled, the following warning will be issued:: Python runtime initialized with LC_CTYPE=C (a locale with default ASCII encoding), which may cause Unicode compatibility problems. Using C.UTF-8 C.utf8, or UTF-8 (if available) as alternative Unicode-compatible locales is recommended. In this case, no actual change will be made to the locale settings. Instead, the warning informs both system and application integrators that they're running Python 3 in a configuration that we don't expect to work properly. The second sentence providing recommendations would be conditionally compiled based on the operating system (e.g. recommending ``LC_CTYPE=UTF-8`` on \*BSD systems. New build-time configuration options ------------------------------------ While both of the above behaviours would be enabled by default, they would also have new associated configuration options and preprocessor definitions for the benefit of redistributors that want to override those default settings. The locale coercion behaviour would be controlled by the flag ``--with[out]-c-locale-coercion``, which would set the ``PY_COERCE_C_LOCALE`` preprocessor definition. The locale warning behaviour would be controlled by the flag ``--with[out]-c-locale-warning``, which would set the ``PY_WARN_ON_C_LOCALE`` preprocessor definition. On platforms where they would have no effect (e.g. Mac OS X, iOS, Android, Windows) these preprocessor variables would always be undefined. Platform Support Changes ======================== A new "Legacy C Locale" section will be added to PEP 11 that states: * as of CPython 3.7, the legacy C locale is only supported when operating in "UTF-8" mode. Any Unicode handling issues that occur only in that locale and cannot be reproduced in an appropriately configured non-ASCII locale will be closed as "won't fix" * as of CPython 3.7, \*nix platforms are expected to provide at least one of ``C.UTF-8`` (full locale), ``C.utf8`` (full locale) or ``UTF-8`` ( ``LC_CTYPE``-only locale) as an alternative to the legacy ``C`` locale. Any Unicode related integration problems with C/C++ extensions that occur only in that locale and cannot be reproduced in an appropriately configured non-ASCII locale will be closed as "won't fix". Rationale ========= Improving the handling of the C locale -------------------------------------- It has been clear for some time that the C locale's default encoding of ``ASCII`` is entirely the wrong choice for development of modern networked services. Newer languages like Rust and Go have eschewed that default entirely, and instead made it a deployment requirement that systems be configured to use UTF-8 as the text encoding for operating system interfaces. Similarly, Node.js assumes UTF-8 by default (a behaviour inherited from the V8 JavaScript engine) and requires custom build settings to indicate it should use the system locale settings for locale-aware operations. Both the JVM and the .NET CLR use UTF-16-LE as their primary encoding for passing text between applications and the underlying platform. The challenge for CPython has been the fact that in addition to being used for network service development, it is also extensively used as an embedded scripting language in larger applications, and as a desktop application development language, where it is more important to be consistent with other C/C++ components sharing the same process, as well as with the user's desktop locale settings, than it is with the emergent conventions of modern network service development. The core premise of this PEP is that for *all* of these use cases, the assumption of ASCII implied by the default "C" locale is the wrong choice, and furthermore that the following assumptions are valid: * in desktop application use cases, the process locale will *already* be configured appropriately, and if it isn't, then that is an operating system or embedding application level problem that needs to be reported to and resolved by the operating system provider or application developer * in network service development use cases (especially those based on Linux containers), the process locale may not be configured *at all*, and if it isn't, then the expectation is that components will impose their own default encoding the way Rust, Go and Node.js do, rather than trusting the legacy C default encoding of ASCII the way CPython currently does Defaulting to "surrogateescape" error handling on the standard IO streams ------------------------------------------------------------------------- By coercing the locale away from the legacy C default and its assumption of ASCII as the preferred text encoding, this PEP also disables the implicit use of the "surrogateescape" error handler on the standard IO streams that was introduced in Python 3.5 ([15_]), as well as the automatic use of ``surrogateescape`` when operating in PEP 540's UTF-8 mode. Rather than introducing yet another configuration option to address that, this PEP proposes to use the existing ``PYTHONIOENCODING`` setting to ensure that the ``surrogateescape`` handler is enabled when the interpreter is required to make assumptions regarding the expected filesystem encoding. The aim of this behaviour is to attempt to ensure that operating system provided text values are typically able to be transparently passed through a Python 3 application even if it is incorrect in assuming that that text has been encoded as UTF-8. In particular, GB 18030 [12_] is a Chinese national text encoding standard that handles all Unicode code points, that is formally incompatible with both ASCII and UTF-8, but will nevertheless often tolerate processing as surrogate escaped data - the points where GB 18030 reuses ASCII byte values in an incompatible way are likely to be invalid in UTF-8, and will therefore be escaped and opaque to string processing operations that split on or search for the relevant ASCII code points. Operations that don't involve splitting on or searching for particular ASCII or Unicode code point values are almost certain to work correctly. Similarly, Shift-JIS [13_] and ISO-2022-JP [14_] remain in widespread use in Japan, and are incompatible with both ASCII and UTF-8, but will tolerate text processing operations that don't involve splitting on or searching for particular ASCII or Unicode code point values. As an example, consider two files, one encoded with UTF-8 (the default encoding for ``en_AU.UTF-8``), and one encoded with GB-18030 (the default encoding for ``zh_CN.gb18030``):: $ python3 -c 'open("utf8.txt", "wb").write("ℙƴ☂ℌøἤ\n".encode("utf-8"))' $ python3 -c 'open("gb18030.txt", "wb").write("ℙƴ☂ℌøἤ\n".encode("gb18030"))' On disk, we can see that these are two very different files:: $ python3 -c 'print("UTF-8: ", open("utf8.txt", "rb").read().strip()); \ print("GB18030:", open("gb18030.txt", "rb").read().strip())' UTF-8: b'\xe2\x84\x99\xc6\xb4\xe2\x98\x82\xe2\x84\x8c\xc3\xb8\xe1\xbc\xa4\n' GB18030: b'\x816\xbd6\x810\x9d0\x817\xa29\x816\xbc4\x810\x8b3\x816\x8d6\n' That nevertheless can both be rendered correctly to the terminal as long as they're decoded prior to printing:: $ python3 -c 'print("UTF-8: ", open("utf8.txt", "r", encoding="utf-8").read().strip()); \ print("GB18030:", open("gb18030.txt", "r", encoding="gb18030").read().strip())' UTF-8: ℙƴ☂ℌøἤ GB18030: ℙƴ☂ℌøἤ By contrast, if we just pass along the raw bytes, as ``cat`` and similar C/C++ utilities will tend to do:: $ LANG=en_AU.UTF-8 cat utf8.txt gb18030.txt ℙƴ☂ℌøἤ �6�6�0�0�7�9�6�4�0�3�6�6 Even setting a specifically Chinese locale won't help in getting the GB-18030 encoded file rendered correctly:: $ LANG=zh_CN.gb18030 cat utf8.txt gb18030.txt ℙƴ☂ℌøἤ �6�6�0�0�7�9�6�4�0�3�6�6 The problem is that the *terminal* encoding setting remains UTF-8, regardless of the nominal locale. A GB18030 terminal can be emulated using the ``iconv`` utility:: $ cat utf8.txt gb18030.txt | iconv -f GB18030 -t UTF-8 鈩櫰粹槀鈩屆羔激 ℙƴ☂ℌøἤ This reverses the problem, such that the GB18030 file is rendered correctly, but the UTF-8 file has been converted to unrelated hanzi characters, rather than the expected rendering of "Python" as non-ASCII characters. With the emulated GB18030 terminal encoding, assuming UTF-8 in Python results in *both* files being displayed incorrectly:: $ python3 -c 'print("UTF-8: ", open("utf8.txt", "r", encoding="utf-8").read().strip()); \ print("GB18030:", open("gb18030.txt", "r", encoding="gb18030").read().strip())' \ | iconv -f GB18030 -t UTF-8 UTF-8: 鈩櫰粹槀鈩屆羔激 GB18030: 鈩櫰粹槀鈩屆羔激 However, setting the locale correctly means that the emulated GB18030 terminal now displays both files as originally intended:: $ LANG=zh_CN.gb18030 \ python3 -c 'print("UTF-8: ", open("utf8.txt", "r", encoding="utf-8").read().strip()); \ print("GB18030:", open("gb18030.txt", "r", encoding="gb18030").read().strip())' \ | iconv -f GB18030 -t UTF-8 UTF-8: ℙƴ☂ℌøἤ GB18030: ℙƴ☂ℌøἤ The rationale for retaining ``surrogateescape`` as the default IO encoding is that it will preserve the following helpful behaviour in the C locale:: $ cat gb18030.txt \ | LANG=C python3 -c "import sys; print(sys.stdin.read())" \ | iconv -f GB18030 -t UTF-8 ℙƴ☂ℌøἤ Rather than reverting to the exception seen when a UTF-8 based locale is explicitly configured:: $ cat gb18030.txt \ | python3 -c "import sys; print(sys.stdin.read())" \ | iconv -f GB18030 -t UTF-8 Traceback (most recent call last): File "<string>", line 1, in <module> File "/usr/lib64/python3.5/codecs.py", line 321, in decode (result, consumed) = self._buffer_decode(data, self.errors, final) UnicodeDecodeError: 'utf-8' codec can't decode byte 0x81 in position 0: invalid start byte Note: an alternative to setting ``PYTHONIOENCODING`` as the PEP currently proposes would be to instead *always* default to ``surrogateescape`` on the standard streams, and require the use of ``PYTHONIOENCODING=:strict`` to request text encoding validation during stream processing. Adopting such an approach would bring Python 3 more into line with typical C/C++ tools that pass along the raw bytes without checking them for conformance to their nominal encoding, and would hence also make the last example display the desired output:: $ cat gb18030.txt \ | PYTHONIOENCODING=:surrogateescape python3 -c "import sys; print(sys.stdin.read())" \ | iconv -f GB18030 -t UTF-8 ℙƴ☂ℌøἤ Dropping official support for ASCII based text handling in the legacy C locale ------------------------------------------------------------------------------ We've been trying to get strict bytes/text separation to work reliably in the legacy C locale for over a decade at this point. Not only haven't we been able to get it to work, neither has anyone else - the only viable alternatives identified have been to pass the bytes along verbatim without eagerly decoding them to text (C/C++, Python 2.x, Ruby, etc), or else to ignore the nominal C/C++ locale encoding entirely and assume the use of either UTF-8 (PEP 540, Rust, Go, Node.js, etc) or UTF-16-LE (JVM, .NET CLR). While this PEP ensures that developers that need to do so can still opt-in to running their Python code in the legacy C locale, it also makes clear that we *don't* expect Python 3's Unicode handling to be reliable in that configuration, and the recommended alternative is to use a more appropriate locale setting. Providing implicit locale coercion only when running standalone --------------------------------------------------------------- Over the course of Python 3.x development, multiple attempts have been made to improve the handling of incorrect locale settings at the point where the Python interpreter is initialised. The problem that emerged is that this is ultimately *too late* in the interpreter startup process - data such as command line arguments and the contents of environment variables may have already been retrieved from the operating system and processed under the incorrect ASCII text encoding assumption well before ``Py_Initialize`` is called. The problems created by those inconsistencies were then even harder to diagnose and debug than those created by believing the operating system's claim that ASCII was a suitable encoding to use for operating system interfaces. This was the case even for the default CPython binary, let alone larger C/C++ applications that embed CPython as a scripting engine. The approach proposed in this PEP handles that problem by moving the locale coercion as early as possible in the interpreter startup sequence when running standalone: it takes place directly in the C-level ``main()`` function, even before calling in to the `Py_Main()`` library function that implements the features of the CPython interpreter CLI. The ``Py_Initialize`` API then only gains an explicit warning (emitted on ``stderr``) when it detects use of the ``C`` locale, and relies on the embedding application to specify something more reasonable. Querying LC_CTYPE for C locale detection ---------------------------------------- ``LC_CTYPE`` is the actual locale category that CPython relies on to drive the implicit decoding of environment variables, command line arguments, and other text values received from the operating system. As such, it makes sense to check it specifically when attempting to determine whether or not the current locale configuration is likely to cause Unicode handling problems. Setting both LANG & LC_ALL for C.UTF-8 locale coercion ------------------------------------------------------ Python is often used as a glue language, integrating other C/C++ ABI compatible components in the current process, and components written in arbitrary languages in subprocesses. Setting ``LC_ALL`` to ``C.UTF-8`` imposes a locale setting override on all C/C++ components in the current process and in any subprocesses that inherit the current environment. This is important to handle cases where the problem has arisen from a setting like ``LC_CTYPE=UTF-8`` being provided on a system where no ``UTF-8`` locale is defined (e.g. when a Mac OS X ssh client is configured to forward locale settings, and the user logs into a Linux server). Setting ``LANG`` to ``C.UTF-8`` ensures that even components that only check the ``LANG`` fallback for their locale settings will still use ``C.UTF-8``. Together, these should ensure that when the locale coercion is activated, the switch to the C.UTF-8 locale will be applied consistently across the current process and any subprocesses that inherit the current environment. Allowing restoration of the legacy behaviour -------------------------------------------- The CPython command line interpreter is often used to investigate faults that occur in other applications that embed CPython, and those applications may still be using the C locale even after this PEP is implemented. Providing a simple on/off switch for the locale coercion behaviour makes it much easier to reproduce the behaviour of such applications for debugging purposes, as well as making it easier to reproduce the behaviour of older 3.x runtimes even when running a version with this change applied. Implementation ============== A draft implementation of the change (including test cases and documentation) is linked from issue 28180 [1_], which is an end user request that ``sys.getfilesystemencoding()`` default to ``utf-8`` rather than ``ascii``. This patch is now being maintained as the ``pep538-coerce-c-locale`` feature branch [18_] in Nick Coghlan's fork of the CPython repository on GitHub. NOTE: As discussed in [1_], the currently posted draft implementation has some known issues on Android. Backporting to earlier Python 3 releases ======================================== Backporting to Python 3.6.0 --------------------------- If this PEP is accepted for Python 3.7, redistributors backporting the change specifically to their initial Python 3.6.0 release will be both allowed and encouraged. However, such backports should only be undertaken either in conjunction with the changes needed to also provide a suitable locale by default, or else specifically for platforms where such a locale is already consistently available. Backporting to other 3.x releases --------------------------------- While the proposed behavioural change is seen primarily as a bug fix addressing Python 3's current misbehaviour in the default ASCII-based C locale, it still represents a reasonably significant change in the way CPython interacts with the C locale system. As such, while some redistributors may still choose to backport it to even earlier Python 3.x releases based on the needs and interests of their particular user base, this wouldn't be encouraged as a general practice. However, configuring Python 3 *environments* (such as base container images) to use these configuration settings by default is both allowed and recommended. Acknowledgements ================ The locale coercion approach proposed in this PEP is inspired directly by Armin Ronacher's handling of this problem in the ``click`` command line utility development framework [2_]:: $ LANG=C python3 -c 'import click; cli = click.command()(lambda:None); cli()' Traceback (most recent call last): ... RuntimeError: Click will abort further execution because Python 3 was configured to use ASCII as encoding for the environment. Either run this under Python 2 or consult http://click.pocoo.org/python3/ for mitigation steps. This system supports the C.UTF-8 locale which is recommended. You might be able to resolve your issue by exporting the following environment variables: export LC_ALL=C.UTF-8 export LANG=C.UTF-8 The change was originally proposed as a downstream patch for Fedora's system Python 3.6 package [3_], and then reformulated as a PEP for Python 3.7 with a section allowing for backports to earlier versions by redistributors. The initial draft was posted to the Python Linux SIG for discussion [10_] and then amended based on both that discussion and Victor Stinner's work in PEP 540 [11_]. The "ℙƴ☂ℌøἤ" string used in the Unicode handling examples throughout this PEP is taken from Ned Batchelder's excellent "Pragmatic Unicode" presentation [9_]. Stephen Turnbull has long provided valuable insight into the text encoding handling challenges he regularly encounters at the University of Tsukuba (筑波大学). References ========== .. [1] CPython: sys.getfilesystemencoding() should default to utf-8 (http://bugs.python.org/issue28180) .. [2] Locale configuration required for click applications under Python 3 (http://click.pocoo.org/5/python3/#python-3-surrogate-handling) .. [3] Fedora: force C.UTF-8 when Python 3 is run under the C locale (https://bugzilla.redhat.com/show_bug.cgi?id=1404918) .. [4] GNU C: How Programs Set the Locale ( https://www.gnu.org/software/libc/manual/html_node/Setting-the-Locale.html) .. [5] GNU C: Locale Categories ( https://www.gnu.org/software/libc/manual/html_node/Locale-Categories.html) .. [6] glibc C.UTF-8 locale proposal (https://sourceware.org/glibc/wiki/Proposals/C.UTF-8) .. [7] GNOME Flatpak (http://flatpak.org/) .. [8] Ubuntu Snappy (https://www.ubuntu.com/desktop/snappy) .. [9] Pragmatic Unicode (http://nedbatchelder.com/text/unipain.html) .. [10] linux-sig discussion of initial PEP draft (https://mail.python.org/pipermail/linux-sig/2017-January/000014.html) .. [11] Feedback notes from linux-sig discussion and PEP 540 (https://github.com/python/peps/issues/171) .. [12] GB 18030 (https://en.wikipedia.org/wiki/GB_18030) .. [13] Shift-JIS (https://en.wikipedia.org/wiki/Shift_JIS) .. [14] ISO-2022 (https://en.wikipedia.org/wiki/ISO/IEC_2022) .. [15] Use "surrogateescape" error handler for sys.stdin and sys.stdout on UNIX for the C locale (https://bugs.python.org/issue19977) .. [16] test_readline.test_nonascii fails on Android (http://bugs.python.org/issue28997) .. [17] UTF-8 locale discussion on "locale.getdefaultlocale() fails on Mac OS X with default language set to English" (http://bugs.python.org/issue18378#msg215215) .. [18] GitHub branch diff for ``ncoghlan:pep538-coerce-c-locale`` ( https://github.com/python/cpython/compare/master...ncoghlan:pep538-coerce-c… ) Copyright ========= This document has been placed in the public domain under the terms of the CC0 1.0 license: https://creativecommons.org/publicdomain/zero/1.0/ -- Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia

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I will be deleting the cpython-mirror repo on April 10
by Brett Cannon 10 Apr '17

10 Apr '17

On the two-month anniversary of the GitHub migration I'm going to delete the old git mirror: https://github.com/python/cpython-mirror. If you have a old PR that got closed with comments or something, now is the time to get those comments off.

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why _PyGen_Finalize(gen) propagates close() to _PyGen_yf() ?
by Oleg Nesterov 03 Apr '17

03 Apr '17

Hello, Let me first clarify, I do not claim this is a bug, I am trying to learn python and now I trying to understand yield-from. This simple test-case g = (x for x in range(10)) def fg(): for x in g: yield x print(next(fg())) print(next(g)) works as expected and prints: 0 1 However, if I change fg() to use yield-from g = (x for x in range(10)) def fg(): yield from g print(next(fg())) print(next(g)) then next(g) raises StopIteration: 0 Traceback (most recent call last): File "/tmp/T.py", line 10, in <module> print(next(g)) StopIteration because g.close() is called by destructor of the object returned by fg(). To me this looks strange and confusing. I tried to google, and found https://docs.python.org/3/whatsnew/3.3.html#pep-380 but it doesn't document this behaviour. I understand that yield-from should propagate .close(), but why _PyGen_Finalize() should send close() to the gi_yieldfrom object? I applied the patch below just to verify that I actually understand what's going on, and with this patch the 2nd test-case works as I'd expect. But since I am very new to python I'd suspect that the code is fine and I simply do not understand why it works this way. So. could someone please explain the rationale behind this behaviour? And probably update the docs should be updated? Thanks in advance. Oleg. --- diff --git a/Objects/genobject.c b/Objects/genobject.c index 24a1da6..d5152eb 100644 --- a/Objects/genobject.c +++ b/Objects/genobject.c @@ -6,6 +6,7 @@ #include "opcode.h" static PyObject *gen_close(PyGenObject *, PyObject *); +static PyObject *do_gen_close(PyGenObject *, PyObject *); static PyObject *async_gen_asend_new(PyAsyncGenObject *, PyObject *); static PyObject *async_gen_athrow_new(PyAsyncGenObject *, PyObject *); @@ -71,7 +72,7 @@ _PyGen_Finalize(PyObject *self) } } else { - res = gen_close(gen, NULL); + res = do_gen_close(gen, NULL); } if (res == NULL) { @@ -373,10 +374,9 @@ _PyGen_yf(PyGenObject *gen) } static PyObject * -gen_close(PyGenObject *gen, PyObject *args) +do_gen_close(PyGenObject *gen, PyObject *yf) { PyObject *retval; - PyObject *yf = _PyGen_yf(gen); int err = 0; if (yf) { @@ -407,6 +407,11 @@ gen_close(PyGenObject *gen, PyObject *args) return NULL; } +static PyObject * +gen_close(PyGenObject *gen, PyObject *args) +{ + return do_gen_close(gen, _PyGen_yf(gen)); +} PyDoc_STRVAR(throw_doc, "throw(typ[,val[,tb]]) -> raise exception in generator,\n\

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__del__ is not called after creating a new reference
by Oleg Nesterov 02 Apr '17

02 Apr '17

Hello, I already tried to ask on python-list, see https://mail.python.org/pipermail/python-list/2017-March/720037.html but it seems that this list is not for technical questions. Let me resend my question to python-dev. Please tell me if I should not spam this list with newbiesh questions, and thanks in advance. --------------------------------------------------------------------------- I started to learn python a few days ago and I am trying to understand what __del__() actually does. https://docs.python.org/3/reference/datamodel.html says: object.__del__(self) ... Note that it is possible (though not recommended!) for the __del__() method to postpone destruction of the instance by creating a new reference to it. It may then be called at a later time when this new reference is deleted. However, this trivial test-case class C: def __del__(self): print("DEL") global X X = self C() print(X) X = 0 print(X) shows that __del__ is called only once, it is not called again after "X = 0": DEL <__main__.C object at 0x7f067695f4a8> 0 (Just in case, I verified later that this object actually goes away and its memory is freed, so the problem is not that it still has a reference). I've cloned https://github.com/python/cpython.git and everything looks clear at first glance (but let me repeat that I am very new to python): PyObject_CallFinalizerFromDealloc() calls PyObject_CallFinalizer() which finally calls "__del__" method in slot_tp_finalize(), then it notices that "X = self" creates the new reference and does: /* tp_finalize resurrected it! Make it look like the original Py_DECREF * never happened. */ refcnt = self->ob_refcnt; _Py_NewReference(self); self->ob_refcnt = refcnt; However, PyObject_CallFinalizer() also does _PyGC_SET_FINALIZED(self, 1) and that is why __del__ is not called again after "X = 0": /* tp_finalize should only be called once. */ if (PyType_IS_GC(tp) && _PyGC_FINALIZED(self)) return; The comment and the code are very explicit, so this does nt look like a bug in cpython. Probably the docs should be fixed? Or this code is actually wrong? The test-case works as documented if I remove _PyGC_SET_FINALIZED() in PyObject_CallFinalizer() or add another _PyGC_SET_FINALIZED(self, 0) into PyObject_CallFinalizerFromDealloc() after _Py_NewReference(self), but yes, yes, I understand that this is not correct and won't really help. Oleg.

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Python-Dev March 2017