Mailman 3 August 2010 - 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

http://www.pythonlabs.com/logos.html is gone
by Georg Brandl 08 Feb '11

08 Feb '11

Which I noticed since it's cited in the BeOpen license we still refer to in LICENSE. Since pythonlabs.com itself is still up, it probably isn't much work to make the logos.html URI work again, but I don't know who maintains that page. cheer, Georg -- Thus spake the Lord: Thou shalt indent with four spaces. No more, no less. Four shall be the number of spaces thou shalt indent, and the number of thy indenting shall be four. Eight shalt thou not indent, nor either indent thou two, excepting that thou then proceed to four. Tabs are right out.

2 3

Add aware local time support to datetime module
by Alexander Belopolsky 13 Oct '10

13 Oct '10

[I've got no response from python-ideas, so I am forwarding to python-dev.] With addition of fixed offset timezone class and the timezone.utc instance [0], it is easy to get UTC time as an aware datetime instance: >>> datetime.now(timezone.utc) datetime.datetime(2010, 8, 3, 14, 16, 10, 670308, tzinfo=datetime.timezone.utc) However, if you want to keep time in your local timezone, getting an aware datetime is almost a catch 22. If you know your timezone UTC offset, you can do >>> EDT = timezone(timedelta(hours=-4)) >>> datetime.now(EDT) datetime.datetime(2010, 8, 3, 10, 20, 23, 769537, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000))) but the problem is that there is no obvious or even correct way to find local timezone UTC offset. [1] In a comment on issue #5094 ("datetime lacks concrete tzinfo implementation for UTC"), I proposed to address this problem in a localtime([t]) function that would return current time (or time corresponding to the optional datetime argument) as an aware datetime object carrying local timezone information in a tzinfo set to an appropriate timezone instance. This solution is attractive by its simplicity, but there are several problems: 1. An aware datetime cannot carry all information that system localtime() supplies in a time tuple. Specifically, the is_dst flag is lost. This is not a problem for most applications as long as timezone UTC offset and timezone name are available, but may be an issue when interoperability with the time module is required. 2. Datetime's tzinfo interface was designed with the idea that <2010-11-06 12:00 EDT> + <1 day> = <2010-11-07 12:00 EST>, not <2010-11-07 12:00 EDT>. It other words, if I have lunch with someone at noon (12:00 EDT) on Saturday the day before first Sunday in November, and want to meet again "at the same time tomorrow", I mean 12:00 EST, not 24 hours later. With localtime() returning datetime with tzinfo set to fixed offset timezone, however, localtime() + timedelta(1) will mean exactly 24 hours later and the result will be expressed in an unusual for the given location timezone. An alternative approach is the one recommended in the python manual. [3] One could implement a LocalTimezone class with utcoffset(), tzname() and dst() extracting information from system mktime and localtime calls. This approach has its own shortcomings: 1. While adding integral number of days to datetimes in business setting, it is natural to expect automatic timezone adjustments, it is not as clearcut when adding hours or minutes. 2. The tzinfo.utcoffset() interface that expects *standard* local time as an argument is confusing to many users. Even the "official" example in the python manual gets it wrong. [4] 3. datetime(..., tzinfo=LocalTimezone()) is ambiguous during the "repeated hour" when local clock is set back in DST to standard time transition. As far as I can tell, the only way to resolve the last problem is to add is_dst flag to the datetime object, which would also be the only way to achieve full interoperability between datetime objects and time tuples. [5] The traditional answer to call for improvement of timezone support in datetime module has been: "this is upto 3rd parties to implement." Unfortunately, stdlib is asking 3rd parties to implement an impossible interface without giving access to the necessary data. The impossibility comes from the requirement that dst() method should find out whether local time represents DST or standard time while there is an hour each year when the same local time can be either. The missing data is the system UTC offset when it changes historically. The time module only gives access to the current UTC offset. My preference is to implement the first alternative - localtime([t]) returning aware datetime with fixed offset timezone. This will solve the problem of python's lack of access to the universally available system facilities that are necessary to implement any kind of aware local time support. [0] http://docs.python.org/dev/library/datetime.html#timezone-objects [1] http://bugs.python.org/issue1647654 [2] http://bugs.python.org/issue5094#msg106997 [3] http://docs.python.org/library/datetime.html#tzinfo-objects [4] http://bugs.python.org/issue9063 [5] http://bugs.python.org/issue9004

2 2

Problems with hex-conversion functions
by Ender Wiggin 02 Oct '10

02 Oct '10

Hello everyone. I see several problems with the two hex-conversion function pairs that Python offers: 1. binascii.hexlify and binascii.unhexlify 2. bytes.fromhex and bytes.hex Problem #1: bytes.hex is not implemented, although it was specified in PEP 358. This means there is no symmetrical function to accompany bytes.fromhex. Problem #2: Both pairs perform the same function, although The Zen Of Python suggests that "There should be one-- and preferably only one --obvious way to do it." I do not understand why PEP 358 specified the bytes function pair although it mentioned the binascii pair... Problem #3: bytes.fromhex may receive spaces in the input string, although binascii.unhexlify may not. I see no good reason for these two functions to have different features. Problem #4: binascii.unhexlify may receive both input types: strings or bytes, whereas bytes.fromhex raises an exception when given a bytes parameter. Again there is no reason for these functions to be different. Problem #5: binascii.hexlify returns a bytes type - although ideally, converting to hex should always return string types and converting from hex should always return bytes. IMO there is no meaning of bytes as an output of hexlify, since the output is a representation of other bytes. This is also the suggested behavior of bytes.hex in PEP 358 Problems #4 and #5 call for a decision about the input and output of the functions being discussed: Option A : Strict input and output unhexlify (and bytes.fromhex) may only receives string and may only return bytes hexlify (and bytes.hex) may only receives bytes and may only return strings Option B : Robust input and strict output unhexlify (and bytes.fromhex) may receive bytes and strings and may only return bytes hexlify (and bytes.hex) may receive bytes or strings and may only return strings Of course we may also consider a third option, which will allow the return type of all functions to be robust (perhaps specified in a keyword argument), but as I wrote in the description of problem #5, I see no sense in that. Note that PEP 3137 describes: "... the more strict definitions of encoding and decoding in Python 3000: encoding always takes a Unicode string and returns a bytes sequence, and decoding always takes a bytes sequence and returns a Unicode string." - suggesting option A. To repeat problems #4 and #5, the current behavior does not match any option: * The return type of binascii.hexlify should be string, and this is not the current behavior. As for the input: * Option A is not the current behavior because binascii.unhexlify may receive both input types. * Option B is not the current behavior because bytes.fromhex does not allow bytes as input. To fix these issues, three changes should be applied: 1. Deprecate bytes.fromhex. This fixes the following problems: #4 (go with option B and remove the function that does not allow bytes input) #2 (the binascii functions will be the only way to "do it") #1 (bytes.hex should not be implemented) 2. In order to keep the functionality that bytes.fromhex has over unhexlify, the latter function should be able to handle spaces in its input (fix #3) 3. binascii.hexlify should return string as its return type (fix #5)

5 7

PEP 384 status
by "Martin v. Löwis" 12 Sep '10

12 Sep '10

I have now started an initial patch for PEP 384, in the pep-0384 branch. This has the following features: - modules can be compiled under Py_LIMITED_API - Tools/scripts/abitype.py converts C code containing static PyTypeObject definitions to use the new API for type definitions. The following aspects are still missing: - there is no support for generating python3.dll on Windows yet - there has been no validation whether the API is actually feasible to use in extension modules. I started looking into porting the sqlite extension, and ran into these issues: - certain fields of PyTypeObject are called directly: pysqlite_NodeType.tp_alloc Py_TYPE(self)->tp_free - PyObject_Print is used, but can't be supported, as it uses a FILE* parameter For the first issue, it would be possible to provide a generic accessor function that fetches fields from a type object. Alternatively, each case could be considered, suggesting an alternative code for the desired effect. I'll be off the net for the next two weeks most of the time, so I might not be able to respond quickly. Anybody interested in advancing that patch, feel free to commit changes into the branch. Regards, Martin

15 60

versioned .so files for Python 3.2
by Barry Warsaw 12 Sep '10

12 Sep '10

This is a follow up to PEP 3147. That PEP, already implemented in Python 3.2, allows for Python source files from different Python versions to live together in the same directory. It does this by putting a magic tag in the .pyc file name and placing the .pyc file in a __pycache__ directory. Distros such as Debian and Ubuntu will use this to greatly simplifying deploying Python, and Python applications and libraries. Debian and Ubuntu usually ship more than one version of Python, and currently have to play complex games with symlinks to make this work. PEP 3147 will go a long way to eliminating the need for extra directories and symlinks. One more thing I've found we need though, is a way to handled shared libraries for extension modules. Just as we can get name collisions on foo.pyc, we can get collisions on foo.so. We obviously cannot install foo.so built for Python 3.2 and foo.so built for Python 3.3 in the same location. So symlink nightmare's mini-me is back. I have a fairly simple fix for this. I'd actually be surprised if this hasn't been discussed before, but teh Googles hasn't turned up anything. The idea is to put the Python version number in the shared library file name, and extend .so lookup to find these extended file names. So for example, we'd see foo.3.2.so instead, and Python would know how to dynload both that and the traditional foo.so file too (for backward compatibility). (On file naming: the original patch used foo.so.3.2 and that works just as well, but I thought there might be tools that expect exactly a '.so' suffix, so I changed it to put the Major.Minor version number to the left of the extension. The exact naming scheme is of course open to debate.) This is a much simpler patch than PEP 3147, though I'm not 100% sure it's the right approach. The way this works is by modifying the configure and Makefile.pre.in to put the version number in the $SO make variable. Python parses its (generated) Makefile to find $SO and it uses this deep in the bowels of distutils to decide what suffix to use when writing shared libraries built by 'python setup.py build_ext'. This means the patched Python only writes versioned .so files by default. I personally don't see that as a problem, and it does not affect the test suite, with the exception of one easily tweaked test. I don't know if third party tools will care. The fact that traditional foo.so shared libraries will still satisfy the import should be enough, I think. The patch is currently Linux only, since I need this for Debian and Ubuntu and wanted to keep the change narrow. Other possible approaches: * Extend the distutils API so that the .so file extension can be passed in, instead of being essentially hardcoded to what Python's Makefile contains. * Keep the dynload_shlib.c change, but modify the Debian/Ubuntu build environment to pass in $SO to make (though the configure.in warning and sleep is a little annoying). * Add a ./configure option to enable this, which Debuntu's build would use. The patch is available here: http://pastebin.ubuntu.com/454512/ and my working branch is here: https://code.edge.launchpad.net/~barry/python/sovers Please let me know what you think. I'm happy to just commit this to the py3k branch if there are no objections <wink>. I don't think a new PEP is in order, but an update to PEP 3147 might make sense. Cheers, -Barry

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Thoughts fresh after EuroPython
by Guido van Rossum 08 Sep '10

08 Sep '10

While the EuroPython sprints are still going on, I am back home, and after a somewhat restful night of sleep, I have some thoughts I'd like to share before I get distracted. Note, I am jumping wildly between topics. - Commit privileges: Maybe we've been too careful with only giving commit privileges to to experienced and trusted new developers. I spoke to Ezio Melotti and from his experience with getting commit privileges, it seems to be a case of "the lion is much more afraid of you than you are afraid of the lion". I.e. having got privileges he was very concerned about doing something wrong, worried about the complexity of SVN, and so on. Since we've got lots of people watching the commit stream, I think that there really shouldn't need to be a worry at all about a new committer doing something malicious, and there shouldn't be much worry about honest beginners' mistakes either -- the main worry remains that new committers don't use their privileges enough. So, my recommendation (which surely is a turn-around of my *own* attitude in the past) is to give out more commit privileges sooner. - Concurrency and parallelism: Russel Winder and Sarah Mount pushed the idea of CSP (http://en.wikipedia.org/wiki/Communicating_sequential_processes) in several talks at the conference. They (at least Russell) emphasized the difference between concurrency (interleaved event streams) and parallelism (using many processors to speed things up). Their prediction is that as machines with many processing cores become more prevalent, the relevant architecture will change from cores sharing a single coherent memory (the model on which threads are based) to one where each core has a limited amount of private memory, and communication is done via message passing between the cores. This gives them (and me :-) hope that the GIL won't be a problem as long as we adopt a parallel processing model. Two competing models are the Actor model, which is based on asynchronous communication, and CSP, which is synchronous (when a writer writes to a channel, it blocks until a reader reads that value -- a rendezvous). At least Sarah suggested that both models are important. She also mentioned that a merger is under consideration between the two major CSP-for-Python packages, Py-CSP and Python-CSP. I also believe that the merger will be based on the stdlib multiprocessing package, but I'm not sure. I do expect that we may get some suggestions from that corner to make some minor changes to details of multiprocessing (and perhaps threading), and I think we should be open to those (I expect these will be good suggestions for small tweaks, not major overhauls). - After seeing Raymond's talk about monocle (search for it on PyPI) I am getting excited again about PEP 380 (yield from, return values from generators). Having read the PEP on the plane back home I didn't see anything wrong with it, so it could just be accepted in its current form. Implementation will still have to wait for Python 3.3 because of the moratorium. (Although I wouldn't mind making an exception to get it into 3.2.) - This made me think of how the PEP process should evolve so as to not require my personal approval for every PEP. I think the model for future PEPs should be the one we used for PEP 3148 (futures, which was just approved by Jesse): the discussion is led and moderated by one designated "PEP handler" (a different one for each PEP) and the PEP handler, after reviewing the discussion, decides when the PEP is approved. A PEP handler should be selected for each PEP as soon as possible; without a PEP handler, discussing a PEP is not all that useful. The PEP handler should be someone respected by the community with an interest in the subject of the PEP but at an arms' length (at least) from the PEP author. The PEP handler will have to moderate feedback, separating useful comments from (too much) bikeshedding, repetitious lines of questioning, and other forms of obstruction. The PEP handler should also set and try to maintain a schedule for the discussion. Note that a schedule should not be used to break a tie -- it should be used to stop bikeshedding and repeat discussions, while giving all interested parties a chance to comment. (I should say that this is probably similar to the role of an IETF working group director with respect to RFCs.) - Specifically, if Raymond is interested, I wouldn't mind seeing him as the PEP handler for PEP 380. For some of Martin von Löwis's PEPs (382, 384) I think a PEP handler is sorely lacking -- from the language summit it appeared as if nobody besides Martin understands these PEPs. - A lot of things seem to be happening to make PyPI better. Is this being summarized somewhere? Based on some questions I received during my keynote Q&A (http://bit.ly/bdflqa) I think not enough people are aware of what we are already doing in this area. Frankly, I'm not sure I do, either: I think I've heard of a GSOC student and of plans to take over pypi.appspot.com (with the original developer's permission) to become a full and up-to-date mirror. Mirroring apparently also requires some client changes. Oh, and there's a proposed solution for the "register user" problem where apparently the clients had been broken by a unilateral change to the server to require a certain "yes I agree" checkbox. For a hopefully eventually exhaustive overview of what was accomplished at EuroPython, go to http://wiki.europython.eu/After -- and if you know some blog about EuroPython not yet listed, please add it there. -- --Guido van Rossum (python.org/~guido)

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Two small PEP ideas
by Barry Warsaw 03 Sep '10

03 Sep '10

I have two somewhat unrelated thoughts about PEPs. * Accepted: header When PEP 3147 was accepted, I had a few folks ask that this be recorded in the PEP by including a link to the BDFL pronouncement email. I realized that there's no formal way to express this in a PEP, and many PEPs in fact don't record more than the fact that it was accepted. I'd like to propose officially adding an Accepted: header which should include a URL to the email or other web resource where the PEP is accepted. I've come as close as possible to this (without modifying the supporting scripts or PEP 1) in PEP 3147: http://www.python.org/dev/peps/pep-3147/ I'd be willing to update things if there are no objections. * EOL schedule for older releases. We have semi-formal policies for the lifetimes of Python releases, though I'm not sure this policy is written down in any of the existing informational PEPs. However, we have release schedule PEPs going back to Python 1.6. It seems reasonable to me that we include end-of-life information in those PEPs. For example, we could state that Python 2.4 is no longer even being maintained for security, and we could state the projected date that Python 2.6 will go into security-only maintenance mode. I would not mandate that we go back and update all previous PEPs for either of these ideas. We'd adopt them moving forward and allow anyone who's motivated to backfill information opportunistically. Thoughts? -Barry

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