Mailman 3 July 2011 - 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:

8 14

Reviving restricted mode?
by Guido van Rossum 14 Aug '14

14 Aug '14

I've received some enthusiastic emails from someone who wants to revive restricted mode. He started out with a bunch of patches to the CPython runtime using ctypes, which he attached to an App Engine bug: http://code.google.com/p/googleappengine/issues/detail?id=671 Based on his code (the file secure.py is all you need, included in secure.tar.gz) it seems he believes the only security leaks are __subclasses__, gi_frame and gi_code. (I have since convinced him that if we add "restricted" guards to these attributes, he doesn't need the functions added to sys.) I don't recall the exploits that Samuele once posted that caused the death of rexec.py -- does anyone recall, or have a pointer to the threads? -- --Guido van Rossum (home page: http://www.python.org/~guido/)

19 35

PEP 3145 (With Contents)
by Eric Pruitt 25 Dec '12

25 Dec '12

Alright, I will re-submit with the contents pasted. I never use double backquotes as I think them rather ugly; that is the work of an editor or some automated program in the chain. Plus, it also messed up my line formatting and now I have lines with one word on them... Anyway, the contents of PEP 3145: PEP: 3145 Title: Asynchronous I/O For subprocess.Popen Author: (James) Eric Pruitt, Charles R. McCreary, Josiah Carlson Type: Standards Track Content-Type: text/plain Created: 04-Aug-2009 Python-Version: 3.2 Abstract: In its present form, the subprocess.Popen implementation is prone to dead-locking and blocking of the parent Python script while waiting on data from the child process. Motivation: A search for "python asynchronous subprocess" will turn up numerous accounts of people wanting to execute a child process and communicate with it from time to time reading only the data that is available instead of blocking to wait for the program to produce data [1] [2] [3]. The current behavior of the subprocess module is that when a user sends or receives data via the stdin, stderr and stdout file objects, dead locks are common and documented [4] [5]. While communicate can be used to alleviate some of the buffering issues, it will still cause the parent process to block while attempting to read data when none is available to be read from the child process. Rationale: There is a documented need for asynchronous, non-blocking functionality in subprocess.Popen [6] [7] [2] [3]. Inclusion of the code would improve the utility of the Python standard library that can be used on Unix based and Windows builds of Python. Practically every I/O object in Python has a file-like wrapper of some sort. Sockets already act as such and for strings there is StringIO. Popen can be made to act like a file by simply using the methods attached the the subprocess.Popen.stderr, stdout and stdin file-like objects. But when using the read and write methods of those options, you do not have the benefit of asynchronous I/O. In the proposed solution the wrapper wraps the asynchronous methods to mimic a file object. Reference Implementation: I have been maintaining a Google Code repository that contains all of my changes including tests and documentation [9] as well as blog detailing the problems I have come across in the development process [10]. I have been working on implementing non-blocking asynchronous I/O in the subprocess.Popen module as well as a wrapper class for subprocess.Popen that makes it so that an executed process can take the place of a file by duplicating all of the methods and attributes that file objects have. There are two base functions that have been added to the subprocess.Popen class: Popen.send and Popen._recv, each with two separate implementations, one for Windows and one for Unix based systems. The Windows implementation uses ctypes to access the functions needed to control pipes in the kernel 32 DLL in an asynchronous manner. On Unix based systems, the Python interface for file control serves the same purpose. The different implementations of Popen.send and Popen._recv have identical arguments to make code that uses these functions work across multiple platforms. When calling the Popen._recv function, it requires the pipe name be passed as an argument so there exists the Popen.recv function that passes selects stdout as the pipe for Popen._recv by default. Popen.recv_err selects stderr as the pipe by default. "Popen.recv" and "Popen.recv_err" are much easier to read and understand than "Popen._recv('stdout' ..." and "Popen._recv('stderr' ..." respectively. Since the Popen._recv function does not wait on data to be produced before returning a value, it may return empty bytes. Popen.asyncread handles this issue by returning all data read over a given time interval. The ProcessIOWrapper class uses the asyncread and asyncwrite functions to allow a process to act like a file so that there are no blocking issues that can arise from using the stdout and stdin file objects produced from a subprocess.Popen call. References: [1] [ python-Feature Requests-1191964 ] asynchronous Subprocess http://mail.python.org/pipermail/python-bugs-list/2006-December/ 036524.html [2] Daily Life in an Ivory Basement : /feb-07/problems-with-subprocess http://ivory.idyll.org/blog/feb-07/problems-with-subprocess [3] How can I run an external command asynchronously from Python? - Stack Overflow http://stackoverflow.com/questions/636561/how-can-i-run-an-external- command-asynchronously-from-python [4] 18.1. subprocess - Subprocess management - Python v2.6.2 documentation http://docs.python.org/library/subprocess.html#subprocess.Popen.wait [5] 18.1. subprocess - Subprocess management - Python v2.6.2 documentation http://docs.python.org/library/subprocess.html#subprocess.Popen.kill [6] Issue 1191964: asynchronous Subprocess - Python tracker http://bugs.python.org/issue1191964 [7] Module to allow Asynchronous subprocess use on Windows and Posix platforms - ActiveState Code http://code.activestate.com/recipes/440554/ [8] subprocess.rst - subprocdev - Project Hosting on Google Code http://code.google.com/p/subprocdev/source/browse/doc/subprocess.rst?spec=s… [9] subprocdev - Project Hosting on Google Code http://code.google.com/p/subprocdev [10] Python Subprocess Dev http://subdev.blogspot.com/ Copyright: This P.E.P. is licensed under the Open Publication License; http://www.opencontent.org/openpub/. On Tue, Sep 8, 2009 at 22:56, Benjamin Peterson <benjamin(a)python.org> wrote: > 2009/9/7 Eric Pruitt <eric.pruitt(a)gmail.com>: >> Hello all, >> >> I have been working on adding asynchronous I/O to the Python >> subprocess module as part of my Google Summer of Code project. Now >> that I have finished documenting and pruning the code, I present PEP >> 3145 for its inclusion into the Python core code. Any and all feedback >> on the PEP (http://www.python.org/dev/peps/pep-3145/) is appreciated. > > Hi Eric, > One of the reasons you're not getting many response is that you've not > pasted the contents of the PEP in this message. That makes it really > easy for people to comment on various sections. > > BTW, it seems like you were trying to use reST formatting with the > text PEP layout. Double backquotes only mean something in reST. > > > -- > Regards, > Benjamin >

10 26

Providing a mechanism for PEP 3115 compliant dynamic class creation
by Nick Coghlan 21 Apr '12

21 Apr '12

In reviewing a fix for the metaclass calculation in __build_class__ [1], I realised that PEP 3115 poses a potential problem for the common practice of using "type(name, bases, ns)" for dynamic class creation. Specifically, if one of the base classes has a metaclass with a significant __prepare__() method, then the current idiom will do the wrong thing (and most likely fail as a result), since "ns" will probably be an ordinary dictionary instead of whatever __prepare__() would have returned. Initially I was going to suggest making __build_class__ part of the language definition rather than a CPython implementation detail, but then I realised that various CPython specific elements in its signature made that a bad idea. Instead, I'm thinking along the lines of an "operator.prepare(metaclass, bases)" function that does the metaclass calculation dance, invoking __prepare__() and returning the result if it exists, otherwise returning an ordinary dict. Under the hood we would refactor this so that operator.prepare and __build_class__ were using a shared implementation of the functionality at the C level - it may even be advisable to expose that implementation via the C API as PyType_PrepareNamespace(). The correct idiom for dynamic type creation in a PEP 3115 world would then be: from operator import prepare cls = type(name, bases, prepare(type, bases)) Thoughts? Cheers, Nick. [1] http://bugs.python.org/issue1294232 -- Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia

3 8

Status of the PEP 400? (deprecate codecs.StreamReader/StreamWriter)
by Victor Stinner 22 Oct '11

22 Oct '11

Hi, Three weeks ago, I posted a draft on my PEP on this mailing list. I tried to include all remarks you made, and the PEP is now online: http://www.python.org/dev/peps/pep-0400/ It's now unclear to me if the PEP will be accepted or rejected. I don't know what to do to move forward. Victor

6 11

Latest draft of PEP 399 (Pure Python/C Accelerator Module Compatibility Requirements)
by Brett Cannon 15 Aug '11

15 Aug '11

While at a mini-PyPy sprint w/ Alex Gaynor of PyPy and Phil Jenvey of Jython, I decided to finally put the time in to update this PEP yet again. The biggest changes is that the 100% branch coverage requirement has been replaced with "comprehensive" coverage from the tests. I think we are all enough grown-ups to not have to specify anything tighter than this. I also added a paragraph in the Details section about using the abstract C APIs (e.g., PyObject_GetItem) over type-specific ones (e.g., PyList_GetItem) in order to be more supportive of duck typing from the Python code. I figure the "be API compatible" assumes this, but mentioning it doesn't hurt (and should help make Raymond less angry =). PEP: 399 Title: Pure Python/C Accelerator Module Compatibility Requirements Version: $Revision: 88219 $ Last-Modified: $Date: 2011-01-27 13:47:00 -0800 (Thu, 27 Jan 2011) $ Author: Brett Cannon <brett(a)python.org> Status: Draft Type: Informational Content-Type: text/x-rst Created: 04-Apr-2011 Python-Version: 3.3 Post-History: 04-Apr-2011, 12-Apr-2011, 17-Jul-2011 Abstract ======== The Python standard library under CPython contains various instances of modules implemented in both pure Python and C (either entirely or partially). This PEP requires that in these instances that the C code *must* pass the test suite used for the pure Python code so as to act as much as a drop-in replacement as reasonably possible (C- and VM-specific tests are exempt). It is also required that new C-based modules lacking a pure Python equivalent implementation get special permission to be added to the standard library. Rationale ========= Python has grown beyond the CPython virtual machine (VM). IronPython_, Jython_, and PyPy_ are all currently viable alternatives to the CPython VM. The VM ecosystem that has sprung up around the Python programming language has led to Python being used in many different areas where CPython cannot be used, e.g., Jython allowing Python to be used in Java applications. A problem all of the VMs other than CPython face is handling modules from the standard library that are implemented (to some extent) in C. Since other VMs do not typically support the entire `C API of CPython`_ they are unable to use the code used to create the module. Often times this leads these other VMs to either re-implement the modules in pure Python or in the programming language used to implement the VM itself (e.g., in C# for IronPython). This duplication of effort between CPython, PyPy, Jython, and IronPython is extremely unfortunate as implementing a module *at least* in pure Python would help mitigate this duplicate effort. The purpose of this PEP is to minimize this duplicate effort by mandating that all new modules added to Python's standard library *must* have a pure Python implementation _unless_ special dispensation is given. This makes sure that a module in the stdlib is available to all VMs and not just to CPython (pre-existing modules that do not meet this requirement are exempt, although there is nothing preventing someone from adding in a pure Python implementation retroactively). Re-implementing parts (or all) of a module in C (in the case of CPython) is still allowed for performance reasons, but any such accelerated code must pass the same test suite (sans VM- or C-specific tests) to verify semantics and prevent divergence. To accomplish this, the test suite for the module must have comprehensive coverage of the pure Python implementation before the acceleration code may be added. Details ======= Starting in Python 3.3, any modules added to the standard library must have a pure Python implementation. This rule can only be ignored if the Python development team grants a special exemption for the module. Typically the exemption will be granted only when a module wraps a specific C-based library (e.g., sqlite3_). In granting an exemption it will be recognized that the module will be considered exclusive to CPython and not part of Python's standard library that other VMs are expected to support. Usage of ``ctypes`` to provide an API for a C library will continue to be frowned upon as ``ctypes`` lacks compiler guarantees that C code typically relies upon to prevent certain errors from occurring (e.g., API changes). Even though a pure Python implementation is mandated by this PEP, it does not preclude the use of a companion acceleration module. If an acceleration module is provided it is to be named the same as the module it is accelerating with an underscore attached as a prefix, e.g., ``_warnings`` for ``warnings``. The common pattern to access the accelerated code from the pure Python implementation is to import it with an ``import *``, e.g., ``from _warnings import *``. This is typically done at the end of the module to allow it to overwrite specific Python objects with their accelerated equivalents. This kind of import can also be done before the end of the module when needed, e.g., an accelerated base class is provided but is then subclassed by Python code. This PEP does not mandate that pre-existing modules in the stdlib that lack a pure Python equivalent gain such a module. But if people do volunteer to provide and maintain a pure Python equivalent (e.g., the PyPy team volunteering their pure Python implementation of the ``csv`` module and maintaining it) then such code will be accepted. In those instances the C version is considered the reference implementation in terms of expected semantics. Any new accelerated code must act as a drop-in replacement as close to the pure Python implementation as reasonable. Technical details of the VM providing the accelerated code are allowed to differ as necessary, e.g., a class being a ``type`` when implemented in C. To verify that the Python and equivalent C code operate as similarly as possible, both code bases must be tested using the same tests which apply to the pure Python code (tests specific to the C code or any VM do not follow under this requirement). The test suite is expected to be extensive in order to verify expected semantics. Acting as a drop-in replacement also dictates that no public API be provided in accelerated code that does not exist in the pure Python code. Without this requirement people could accidentally come to rely on a detail in the accelerated code which is not made available to other VMs that use the pure Python implementation. To help verify that the contract of semantic equivalence is being met, a module must be tested both with and without its accelerated code as thoroughly as possible. As an example, to write tests which exercise both the pure Python and C accelerated versions of a module, a basic idiom can be followed:: import collections.abc from test.support import import_fresh_module, run_unittest import unittest c_heapq = import_fresh_module('heapq', fresh=['_heapq']) py_heapq = import_fresh_module('heapq', blocked=['_heapq']) class ExampleTest(unittest.TestCase): def test_heappop_exc_for_non_MutableSequence(self): # Raise TypeError when heap is not a # collections.abc.MutableSequence. class Spam: """Test class lacking many ABC-required methods (e.g., pop()).""" def __len__(self): return 0 heap = Spam() self.assertFalse(isinstance(heap, collections.abc.MutableSequence)) with self.assertRaises(TypeError): self.heapq.heappop(heap) class AcceleratedExampleTest(ExampleTest): """Test using the accelerated code.""" heapq = c_heapq class PyExampleTest(ExampleTest): """Test with just the pure Python code.""" heapq = py_heapq def test_main(): run_unittest(AcceleratedExampleTest, PyExampleTest) if __name__ == '__main__': test_main() If this test were to provide extensive coverage for ``heapq.heappop()`` in the pure Python implementation then the accelerated C code would be allowed to be added to CPython's standard library. If it did not, then the test suite would need to be updated until proper coverage was provided before the accelerated C code could be added. To also help with compatibility, C code should use abstract APIs on objects to prevent accidental dependence on specific types. For instance, if a function accepts a sequence then the C code should default to using `PyObject_GetItem()` instead of something like `PyList_GetItem()`. C code is allowed to have a fast path if the proper `PyList_Check()` is used, but otherwise APIs should work with any object that duck types to the proper interface instead of a specific type. Copyright ========= This document has been placed in the public domain. .. _IronPython: http://ironpython.net/ .. _Jython: http://www.jython.org/ .. _PyPy: http://pypy.org/ .. _C API of CPython: http://docs.python.org/py3k/c-api/index.html .. _sqlite3: http://docs.python.org/py3k/library/sqlite3.html

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[PEPs] Rebooting PEP 394 (aka Support the /usr/bin/python2 symlink upstream)
by Kerrick Staley 13 Aug '11

13 Aug '11

Hi, These are two emails I sent a short while ago about finalizing PEP 394. There was no response, so in case the messages didn't go through, I'm resending them. Thanks, Kerrick Staley ---------- Forwarded message ---------- From: Kerrick Staley <mail(a)kerrickstaley.com> Date: Sat, Jul 9, 2011 at 7:45 PM Subject: Re: [Python-Dev] [PEPs] Support the /usr/bin/python2 symlink upstream To: python-dev(a)python.org Sorry that I dropped the ball on this. I'd still like to see this get implemented, but I got distracted with school and forgot about it. Updates I have made to the PEP will be sent as a patch immediately after this email. Here's a summary of what was happenening when we left off: * The draft SVN version from March 4 was pretty much complete. * Some were concerned about addressing Windows, but it was generally agreed to leave the Windows issue to another PEP. PEP 397 was started on March 15 to address the Windows side of the issue. PEP 397 recommends that the Windows Python launcher read the shebang and use it to determine which Python version to use; this allows one syntax for both operating systems that is compatible with the current PEP 394 recommendation. * There were concerns from Ned Deily about the naming of other binaries such as idle, pydoc, and python-config; these need to be created as idle2, pydoc2, and python2-config, with links created at the locations of the original binaries. * There were concerns from Glenn Linderman that the shebang line doesn't encode enough information to flexibly handle Windows launching (or even launching in general). ==== Here are my thoughts: * For Ned's comments, I agree. Although the issue isn't as large with these programs, there's no reason we can't handle them in the same way. I updated the PEP. * For Glenn's comments, I think the method you propose adds too much complexity. Regardless, if the #@ syntax is implemented, it can be described in PEP 397; it won't have an impact on the contents of this PEP. I think, though, that having multiple syntaxes may cause many scripts to be incompatible with multiple platforms when they don't have to be, since Unix coders will rarely add a #@ line, and Windows coders will likely forget the #! line. Also, #@ really ignores the purpose of a shebang: shebangs simply indicate an interpreter that works with the script; the shebang allows users to run arbitrary scripts without worrying about which interpreter they should specify. There's no reason that a script should use one interpreter on Unix, but be incompatible with that interpreter on Windows yet compatible with another. The name of the Unix binary is enough to determine the implementation and version of the interpreter to be used on Unix, and a Windows launcher should always invoke the same implementation/version on Windows (and this won't require hard-coding anything into the launcher if done right). If you want the script to run with a specific interpreter and version, possibly contingent on which operating system you're running the script under, then you can just invoke the interpreter by name with the script as an argument (e.g. python3 myprogram.py). TL;DR: shebangs encode a default implementation/version, and if you need something special, you can just manually run python3 myprogram.py or use a .bat file. ==== Also, I updated the PEP with the clarification that commands like python3 should be hard links (because they'll be invoked from code and are more efficient; also, hard links are just as flexible as symlinks here), while commands like python should be soft links (because this makes it clear to sysadmins that they can be "switched", and it's needed for flexibility if python3 changes). This really doesn't matter, but can we keep it this way unless there are serious objections? Regards, Kerrick Staley ---------- Forwarded message ---------- From: Kerrick Staley <mail(a)kerrickstaley.com> Date: Sat, Jul 9, 2011 at 7:46 PM Subject: Re: [Python-Dev] [PEPs] Support the /usr/bin/python2 symlink upstream To: python-dev(a)python.org $ svn diff Index: pep-0394.txt =================================================================== --- pep-0394.txt (revision 88860) +++ pep-0394.txt (working copy) @@ -1,5 +1,5 @@ PEP: 394 -Title: The "python" command on Unix-Like Systems +Title: The "python" Command on Unix-Like Systems Version: $Revision$ Last-Modified: $Date$ Author: Kerrick Staley <mail(a)kerrickstaley.com>, @@ -53,10 +53,14 @@ * When reinvoking the interpreter from a Python script, querying ``sys.executable`` to avoid hardcoded assumptions regarding the interpreter location remains the preferred approach. +* The ``idle``, ``pydoc``, and ``python-config`` binaries from Python 2.0 +should likewise be available as ``idle2``, ``pydoc2``, and ``python2-config``, +with the original commands invoking these binaries by default, but possibly +invoking the Python 3.0 versions instead. These recommendations are the outcome of the relevant python-dev discussion in -March 2011 [1] (NOTE: More accurately, they will be such once that "Draft" -status disappears from the PEP header, it has been moved into the "Other +March to July 2011 [1] (NOTE: More accurately, they will be such once that +"Draft" status disappears from the PEP header, it has been moved into the "Other Informational PEP" section in PEP 0 and this note has been deleted) @@ -144,11 +148,16 @@ While technically a new feature, the ``make install`` command and the Mac OS X installer in the 2.7 version of CPython will be adjusted to create the -new ``python2`` command in addition to the existing ``python`` and -``python2.7`` commands. This feature will first appear in CPython 2.7.2. +``python2.7``, ``idle2.7``, ``pydoc2.7``, and ``python2.7-config`` binaries, +with ``python2``, ``idle2``, ``pydoc2``, and ``python2-config`` as hard links +to the respective binaries, and ``python``, ``idle``, ``pydoc``, and +``python-config`` as symbolic links to the respective hard links. This feature +will first appear in CPython 2.7.2. -The ``make install`` command in the CPython 3.x series will continue to -install only the ``python3`` symlink for the foreseeable future. +The ``make install`` command in the CPython 3.x series will similarly install +the ``python3.x``, ``idle3.x``, ``pydoc3.x``, and ``python3.x-config`` binaries +(with appropriate ``x``), and ``python3``, ``idle3``, ``pydoc3``, and +``python3-config`` as hard links. Impact on PYTHON* Environment Variables @@ -166,27 +175,12 @@ Exclusions of MS Windows ======================== -This PEP deliberately excludes any proposals relating to Microsoft Windows. -The use of parallel installs on Windows suffers from numerous issues, -including the "last installed wins" behaviour for handling of file -associations, a lack of universal robust symlink support for easy aliasing of -commands, the fact that the Python executable is not available on ``PATH`` by -default, the fact that the ``python.exe`` and ``pythonw.exe`` names are -used for both Python 2 and Python 3 binaries and the lack of distinction -between the different Python versions when the Start menu shortcuts are -divorced from their containing folders (e.g. when they appear in the -"Recently Used" list. +This PEP deliberately excludes any proposals relating to Microsoft Windows: +devising an equivalent solution for Windows was deemed too complex to handle +here. PEP 397 and the related discussion on the python-dev mailing list address +this issue. -While these questions are well worth addressing, they do not have easy -answers. The authors of this particular PEP aren't inclined to even begin -trying to answer them, but anyone that wants to tackle them should feel free -to start working on their own PEP. -Note that, while the topic has been excluded from this PEP, there is plenty of -material in the linked python-dev discussion that may be useful in the design -and implementation of a Windows-specific solution. - - References ==========

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urllib bug in Python 3.2.1?
by MRAB 10 Aug '11

10 Aug '11

Someone over at StackOverflow has a problem with urlopen in Python 3.2.1: http://stackoverflow.com/questions/6892573/problem-with-urlopen/6892843#689… This is the code: from urllib.request import urlopen f = urlopen('http://online.wsj.com/mdc/public/page/2_3020-tips.html?mod=topnav_2_3000') page = f.read() f.close() With Python 3.1 and Python 3.2.1 it works OK, but with Python 3.2.1 the read returns an empty string (I checked it myself).

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Re: [Python-Dev] cpython (2.7): note Ellipsis syntax
by Georg Brandl 05 Aug '11

05 Aug '11

On 07/30/11 17:00, benjamin.peterson wrote: > http://hg.python.org/cpython/rev/402f94edf11b > changeset: 71637:402f94edf11b > branch: 2.7 > user: Benjamin Peterson <benjamin(a)python.org> > date: Sat Jul 30 09:59:12 2011 -0500 > summary: > note Ellipsis syntax > > files: > Doc/library/stdtypes.rst | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > > diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst > --- a/Doc/library/stdtypes.rst > +++ b/Doc/library/stdtypes.rst > @@ -2930,7 +2930,7 @@ > supports no special operations. There is exactly one ellipsis object, named > :const:`Ellipsis` (a built-in name). > > -It is written as ``Ellipsis``. > +It is written as ``Ellipsis`` or ``...``. In 2.7, this is not true; ``...`` only works in slices there. Georg

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email-6.0.0.a1
by R. David Murray 03 Aug '11

03 Aug '11

OK, so I've released the first iteration of the email6 package on pypi as email-6.0.0a1. After install you import it as email6. This will allow anyone curious and/or motivated to test it out under Python 3.2. I'm especially interested in anyone with a working program that uses email in 3.2: it should be completely backward compatible, and if it isn't I want to know ASAP.[*] I've also opened issue 12586 for review of the delta between default and the code that is in the release. I'd like to check the code in to default and continue to work on it from there. As I said in the issue comments: "When we originally planned out email6 we thought we'd be making a "compatibility break" with backward compatibility shims. As things have turned out the work is more a matter of incremental improvement of the API while maintaining the old API, and thus it seems reasonable to me to work on it directly in default rather than continue to work on it in a separate feature branch." Assuming, that is, that the general approach represented by *this* delta is accepted. What this delta adds to email is a conversion to handling all headers as full blown objects (as opposed to strings, tuples of strings, or Header objects, depending on context). The object type is a subclass of str, so the headers act like strings if you don't use their additional API. The basic additional API is that a 'source' attribute contains the text the generator read from the input source, and a 'value' attribute that contains the value with all the Content-Transfer-Encoding stuff undone so that you have a real unicode string. By changing a policy setting, you can have that value as the string value of the header. You can also assign a string with non-ASCII characters to a header, and the right thing will happen. (Well, eventually it will happen...right now it only works correctly for unstructured headers). Further, Date headers have a datetime attribute (and accept being set to a datetime), and address headers have attributes for accessing the individual addresses in the header. Other structured headers will eventually grow additional attributes as well. The general approach has been discussed with and approved by the email-sig, but all comments are welcome. I know there's room for bikeshedding on some aspects of the API; in some cases I've dome some "placeholder" stuff pending a more complete solution to certain design goals. I have a big project in the offing over the next couple months. QNX is still fully behind the funding for email6 development, but I probably won't be able to complete it until the fall. So I'd like to get this chunk (the biggest chunk of new code, considering the size of the parser) reviewed and checked in if possible. I'll keep working on the bits of functionality that aren't quite complete and the bugs that I know are there until my big project kicks off, but I wanted to release/post now so that there might be a chance of some review happening while I still have time to respond quickly to the feedback. -- R. David Murray http://www.bitdance.com [*] I believe that if you try to use an email6 Message object with the 3.2 mailbox module you will run in to some trouble, but I think it ought to be possible to make it work with the right magic :) PS: I don't have much experience writing parsers, so I'm expecting some critical comments about my parser design. It had to be a custom parser since otherwise I'd be blocked on waiting for some other software to get accepted into the stdlib, but it certainly wound up being a bigger chunk of code than I expected when I started writing it.

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