Mailman 3 April 2003 - 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

RE: [Python-Dev] Those import related syntax errors again...
by Samuele Pedroni 23 Feb '05

23 Feb '05

Hi. [Mark Hammond] > The point isn't about my suffering as such. The point is more that > python-dev owns a tiny amount of the code out there, and I don't believe we > should put Python's users through this. > > Sure - I would be happy to "upgrade" all the win32all code, no problem. I > am also happy to live in the bleeding edge and take some pain that will > cause. > > The issue is simply the user base, and giving Python a reputation of not > being able to painlessly upgrade even dot revisions. I agree with all this. [As I imagined explicit syntax did not catch up and would require lot of discussions.] [GvR] > > Another way is to use special rules > > (similar to those for class defs), e.g. having > > > > <frag> > > y=3 > > def f(): > > exec "y=2" > > def g(): > > return y > > return g() > > > > print f() > > </frag> > > > > # print 3. > > > > Is that confusing for users? maybe they will more naturally expect 2 > > as outcome (given nested scopes). > > This seems the best compromise to me. It will lead to the least > broken code, because this is the behavior that we had before nested > scopes! It is also quite easy to implement given the current > implementation, I believe. > > Maybe we could introduce a warning rather than an error for this > situation though, because even if this behavior is clearly documented, > it will still be confusing to some, so it is better if we outlaw it in > some future version. > Yes this can be easy to implement but more confusing situations can arise: <frag> y=3 def f(): y=9 exec "y=2" def g(): return y return y,g() print f() </frag> What should this print? the situation leads not to a canonical solution as class def scopes. or <frag> def f(): from foo import * def g(): return y return g() print f() </frag> [Mark Hammond] > > This probably won't be a very popular suggestion, but how about pulling > > nested scopes (I assume they are at the root of the problem) > > until this can be solved cleanly? > > Agreed. While I think nested scopes are kinda cool, I have lived without > them, and really without missing them, for years. At the moment the cure > appears worse then the symptoms in at least a few cases. If nothing else, > it compromises the elegant simplicity of Python that drew me here in the > first place! > > Assuming that people really _do_ want this feature, IMO the bar should be > raised so there are _zero_ backward compatibility issues. I don't say anything about pulling nested scopes (I don't think my opinion can change things in this respect) but I should insist that without explicit syntax IMO raising the bar has a too high impl cost (both performance and complexity) or creates confusion. [Andrew Kuchling] > >Assuming that people really _do_ want this feature, IMO the bar should be > >raised so there are _zero_ backward compatibility issues. > > Even at the cost of additional implementation complexity? At the cost > of having to learn "scopes are nested, unless you do these two things > in which case they're not"? > > Let's not waffle. If nested scopes are worth doing, they're worth > breaking code. Either leave exec and from..import illegal, or back > out nested scopes, or think of some better solution, but let's not > introduce complicated backward compatibility hacks. IMO breaking code would be ok if we issue warnings today and implement nested scopes issuing errors tomorrow. But this is simply a statement about principles and raised impression. IMO import * in an inner scope should end up being an error, not sure about 'exec's. We will need a final BDFL statement. regards, Samuele Pedroni.

18 78

2.3b1 release
by Guido van Rossum 08 Aug '03

08 Aug '03

I'd like to do a 2.3b1 release someday. Maybe at the end of next week, that would be Friday April 25. If anyone has something that needs to be done before this release go out, please let me know! Assigning a SF bug or patch to me and setting the priority to 7 is a good way to get my attention. --Guido van Rossum (home page: http://www.python.org/~guido/)

14 51

[PEP] += on return of function call result
by Luke Kenneth Casson Leighton 19 May '03

19 May '03

example code: log = {} for t in range(5): for r in range(10): log.setdefault(r, '') += "test %d\n" % t pprint(log) instead, as the above is not possible, the following must be used: from operator import add ... ... ... add(log.setdefault(r, ''), "test %d\n" % t) ... ARGH! just checked - NOPE! add doesn't work. and there's no function "radd" or "__radd__" in the operator module. unless there are really good reasons, can i recommend allowing += on return result of function calls. i cannot honestly think of or believe that there is a reasonable justification for restricting the += operator. append() on the return result of setdefault works absolutely fine, which is GREAT because you have no idea how long i have been fed up of not being able to do this in one line: log = {} log.setdefault(99, []).append("test %d\n" % t) l.

8 17

os.path.walk() lacks 'depth first' option
by Noah Spurrier 12 May '03

12 May '03

Hello, Recently I realized that there is no easy way to walk a directory tree and rename each directory and file. The standard os.path.walk() function does a breadth first walk. This makes it hard to write scripts that modify directory names as they walk the tree because you need to visit subdirectories before you rename their parents. What is really needed is a depth first walk. For example this naive code would not work with breadth first walk: """Renames all directories and files to lower case.""" import os.path def visit (arg, dirname, names): for name in names: print os.path.join (dirname, name) oldname = os.path.join (dirname, name) newname = os.path.join (dirname, name.lower()) os.rename (oldname, newname) os.path.walk ('.', visit, None) The library source posixpath.py defined os.path.walk on my system. A comment in that file mentions that the visit function may modify the filenames list to impose a different order of visiting, but this is not possible as far as I can tell. Perhaps future versions of Python could include an option to do a depth first walk instead of the default breadth first. Modifying os.path.walk() to allow for optional depth first walking is simple. I have attached a patch to posixpath.py that demonstrates this. This adds an if conditional at the beginning and end of the walk() function. I have not checked to see if other platforms share the posixpath.py module this for the walk() function, but if there is interest then I'd be happy to cross reference this. Yours, Noah *** posixpath.py 2003-04-19 22:26:08.000000000 -0700 --- posixpath_walk_depthfirst.py 2003-04-19 22:12:48.000000000 -0700 *************** *** 259,265 **** # The func may modify the filenames list, to implement a filter, # or to impose a different order of visiting. ! def walk(top, func, arg): """Directory tree walk with callback function. For each directory in the directory tree rooted at top (including top --- 259,265 ---- # The func may modify the filenames list, to implement a filter, # or to impose a different order of visiting. ! def walk(top, func, arg, depthfirst=False): """Directory tree walk with callback function. For each directory in the directory tree rooted at top (including top *************** *** 272,284 **** order of visiting. No semantics are defined for, or required of, arg, beyond that arg is always passed to func. It can be used, e.g., to pass a filename pattern, or a mutable object designed to accumulate ! statistics. Passing None for arg is common.""" try: names = os.listdir(top) except os.error: return ! func(arg, top, names) for name in names: name = join(top, name) try: --- 272,287 ---- order of visiting. No semantics are defined for, or required of, arg, beyond that arg is always passed to func. It can be used, e.g., to pass a filename pattern, or a mutable object designed to accumulate ! statistics. Passing None for arg is common. The optional depthfirst ! argument may be set to True to walk the directory tree depth first. ! The default is False (walk breadth first).""" try: names = os.listdir(top) except os.error: return ! if not depthfirst: ! func(arg, top, names) for name in names: name = join(top, name) try: *************** *** 287,293 **** continue if stat.S_ISDIR(st.st_mode): walk(name, func, arg) ! # Expand paths beginning with '~' or '~user'. # '~' means $HOME; '~user' means that user's home directory. --- 290,297 ---- continue if stat.S_ISDIR(st.st_mode): walk(name, func, arg) ! if depthfirst: ! func(arg, top, names) # Expand paths beginning with '~' or '~user'. # '~' means $HOME; '~user' means that user's home directory. *************** *** 416,420 **** return filename supports_unicode_filenames = False - - --- 420,422 ----

10 18

heaps
by Agthorr 07 May '03

07 May '03

I brought up heapq last week, but there was only brief discussion before the issue got sidetracked into a discussion of FIFO queues. I'd like to revisit heapq. The two people who responded seemed to agree that the existing heapq interface was lacking, and this seemed to be the sentiment many months ago when heapq was added. I'll summarize some of the heap interfaces that have been proposed: - the heapq currently in CVS: - Provides functions to manipulate a list organized as a binary heap - Advantages: - Internal binary heap structure is transparent to user, useful for educational purposes - Low overhead - Already in CVS - My MinHeap/MaxHeap classes: - Provides a class with heap access routines, using a list internally - Advantages: - Implementation is opaque, so it can be replaced later with Fibonacci heaps or Paired heaps without breaking user programs - Provides an adjust_key() command needed by some applications (e.g. Dijkstra's Algorithm) - David Eppstein's priorityDictionary class: - Provides a class with a dictionary-style interface (ex: heap['cat'] = 5 would give 'cat' a priority of 5 in the heap) - Advantages: - Implementation is opaque, so it can be replaced later with Fibonacci heaps or Paired heaps without breaking user programs - A dictionary interface may be more intuitive for certain applications - Limitation: - Objects with the same value may only have a single instance in the heap. I'd very much like to see the current heapq replaced with a different interface in time for 2.3. I believe that an opaque object is better, since it allows more flexibility later. If the current heapq is released, user program will start to use it, and then it will be much more difficult to switch to a different heap algorithm later, should that become desirable. Also, decrease-key is an important feature that many users will expect from a heap; this operation is notably missing from heapq. I'm willing to do whatever work is necessary to get a more flexible heap interface into 2.3. If the consensus prefers my MinHeap (or something similar), I'll gladly write documentation (and have already written rather brutal tests). Somebody with authority, just tell me where to pour my energy in this matter :) -- Agthorr

5 14

New thread death in test_bsddb3
by Tim Peters 03 May '03

03 May '03

test_bsddb3.py fails quickly today under a debug build, with a thread state error, on Win2K, every time. Linux? I assume this is a bad interaction between Mark Hammond's new auto-thread-state code and _bsddb.c's custom thread-manipulation macros: C:\Code\python\PCbuild>python_d ../lib/test/test_bsddb3.py -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Sleepycat Software: Berkeley DB 4.1.25: (December 19, 2002) bsddb.db.version(): (4, 1, 25) bsddb.db.__version__: 4.1.5 bsddb.db.cvsid: $Id: _bsddb.c,v 1.11 2003/03/31 19:51:29 bwarsaw Exp $ python version: 2.3a2+ (#39, Apr 22 2003, 10:48:23) [MSC v.1200 32 bit (I ntel)] -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Fatal Python error: Invalid thread state for this thread C:\Code\python\PCbuild> It's dying in _db_associateCallback, here: static int _db_associateCallback(DB* db, const DBT* priKey, const DBT* priData, DBT* secKey) { int retval = DB_DONOTINDEX; DBObject* secondaryDB = (DBObject*)db->app_private; PyObject* callback = secondaryDB->associateCallback; int type = secondaryDB->primaryDBType; PyObject* key; PyObject* data; PyObject* args; PyObject* result; if (callback != NULL) { MYDB_BEGIN_BLOCK_THREADS; ************ HERE ************* The macro is defined like so: #define MYDB_BEGIN_BLOCK_THREADS { \ PyThreadState* prevState; \ PyThreadState* newState; \ PyEval_AcquireLock(); \ newState = PyThreadState_New(_db_interpreterState); \ prevState = PyThreadState_Swap(newState); PyThreadState_Swap is complaining here: #if defined(Py_DEBUG) if (new) { PyThreadState *check = PyGILState_GetThisThreadState(); if (check && check != new) Py_FatalError("Invalid thread state for this thread"); } #endif This is a new check, I believe it's an intentional check, and I doubt _bsddb.c *should* pass it as-is.

7 12

_socket efficiencies ideas
by Marcus Mendenhall 02 May '03

02 May '03

I have been in discussion recently with Martin v. Loewis about an idea I have been thinking about for a while to improve the efficiency of the connect method in the _socket module. I posted the original suggestion to the python suggestions tracker on sourceforge as item 706392. A bit of history and justification: I am doing a lot of work using python to develop almost-real-time distributed data acquisition and control systems from running laboratory apparatus. In this environment, I do a lot of sun-rpc calls as part of the vxi-11 protocol to allow TCP/IP access to gpib-like devices. As a part of this, I do a lot sock socket.connect() calls, often with the connections being quite transient. The problem is that the current python _socket module makes a DNS call to try to resolve each address before connect is called, which if I am connecting/disconnecting many times a second results in pathological and gratuitous network activity. Incidentally, I am in the process of creating a sourceforge project, pythonlabtools (just approved this morning), in which I will start maintaining a repository of the tools I have been working on. My first solution to this, for which I submitted a patch to the tracker system (with guidance from Martin), was to create a wrapper for the sockaddr object, which one can create in advance, and when _socket.connect() is called (actually when getsockaddrarg() is called by connect), results in an immediate connection without any DNS activity. This solution solves part of the problem, but may not be the right final one. After writing this patch and verifying its functionality, I tried it in the real world. Then, I realized that for sun-rpc work, it wasn't quite what I needed, since the socket number may be changing each time the rpc request is made, resulting in a new address wrapper being needed, and thus DNS activity again. After thinking about what I have done with this patch, I would also like to suggest another change (for which I am also willing to submit the patch, which is quite simple): Consistent with some of the already extant glue in _socket to handle addresses like <broadcast>, would there be any reason no to modify setipaddr() and getaddrinfo() so that if an address is prefixed with <numeric> (e.g. <numeric>127.0.0.1) that the PASSIVE and NUMERIC flags are always set so these routines reject any non-numeric address, but handle numeric ones very efficiently? I have already implemented a predecessor to this which I am experimentally running at home in python 2.2.2, in which I made it so that prefixing the address with an exclamation point provided this functionality. Given the somewhat more legible approach the team has already chosen for special addresses, I see no reason why using a <numeric> (or some such) prefix isn't reasonable. Do any members of the development team have commentary on this? Would such a change be likely to be accepted into the system? Any reasons which it might break something? The actual patch would be only about 10 lines of code, (plus some documentation), a few in each of the routines mentioned above. Thanks for any suggestions. Marcus Mendenhall

14 43

Re: Python-Dev digest, Vol 1 #3221 - 4 msgs
by Glyph Lefkowitz 01 May '03

01 May '03

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Monday, April 28, 2003, at 11:00 AM, python-dev-request(a)python.org wrote: > Itamar> If this slowdown is confirmed, it is really not acceptable, > Itamar> since the change seems to have been made only to support > making > Itamar> timeout sockets slightly easier to use. > > It was done to support making timeout sockets work properly. As they > existed previously, timeout sockets wouldn't work with protocols which > would > most likely use them: higher level modules such as httplib, which call > sock.makefile(), then call readlines?() on the resulting file object. Clearly this is a flaw in httplib's design. Perhaps one should be able to pass in a socket or file factory? That would allow speaking HTTP over non-TCP transports or through something like a SOCKS proxy, which is arguably a good thing. Do you want to add SOCKS support by adding another wrapper around the socket module as well? How about a python software firewall? Pretty soon our "correct" socket module will have 20 performance-destroying wrappers around it in order to work around deficiencies in the interfaces of some programs which use sockets. httplib is importing a module where passing a factory function is the correct thing to do. At first it looks like you can parameterize it by hacking up a module, but you can only do that once or twice before the design problem really becomes pressing. The socket module is not a high-level interface to networking. Attempting to make it into one will harm its utility as a low-level interface that good high-level interfaces can be built on top of. > Itamar> Why should everyone have to pay a speed penalty just so a > Itamar> minority of people can skip calling a > Itamar> "socket.installtimeoutsupport()" at the beginning of their > Itamar> program? it's just one line of code they'd need to add. > > I think it would be easier for the minority of programs that care > about the > 20% performance loss to simply set I think this should be in the release notes for 2.3. "Python is 10% faster, unless you use sockets, in which case it is much, much slower. Do the following in order to regain lost performance and retain the same semantics:" I anticipate that more than just Twisted will want to monkey-patch the module. (A 20% drop in throughput is a significant issue to more than an eclectic audience.) If you're not going to fix this bug, maybe we could have a "socket.monkeypatch()" method which would prevent different systems from stepping on each other when they do it? > I don't know about you, but fast and incorrect don't help me much. Since when is the behavior of the socket module "incorrect"? If anything the interface to "timeout sockets" is incorrect, because BSD sockets do not in fact support timeouts. The interface is doing a bunch of things behind the user's back which would be better done another way, for example, with actually asynchronous networking. It's pretty likely that there is some obscure corner-case that the select() in timeout sockets doesn't catch. From a brief glance, internal_select ignores error return values, and nothing checks its errno before making another socket call. If I remember correctly, that means that if select gets an EINTR, the following call to accept() or recv() or what-have-you may very well block. Of course, since the socket is in non-blocking mode at this point, that means that Python will raise an exception on the EAGAIN EWOULDBLOCK error. This is pretty hard to write a test for. I could be wrong about this particular error, but in general if one wishes to be pedantic about "correctness", one must first check the result codes from one's C system calls. > Feel free to submit a patch which improves performance but maintains > proper behavior in the face of timeouts (that is, allows > test_urllibnet to still work correctly). Why is the Python development team introducing bugs into Python and then expecting the user community to fix things that used to work? I could understand not wanting to put a lot of effort into correcting obscure or difficult-to-find performance problems that only a few people care about, but the obvious thing to do in this case is simply to change the default behavior. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (Darwin) iD8DBQE+rZPbvVGR4uSOE2wRAhZVAKCjWkl1NSr8bC1DGcbvhKwL4GZ9+ACeO2cJ FNU17XosCZxRTVRF/wIkLys= =GJ3H -----END PGP SIGNATURE-----

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Initialization hook for extenders
by Patrick J. Miller 01 May '03

01 May '03

I work on several projects that have initialization requirements that need to grab control after Py_Initialize(), but before any user code runs (via input, script, -c, etc...). Note that these are Python clones that take advantage of an installed python (using its $prefix/lib/pythonx.x/*.py and site-packages/*) We could use PyImport_AppendInittab("sitecustomize",initsitecustomize); But if there already IS customization in sitecustomize.py, I've blown it away (and have to look it up and force an import). And if someone uses the -S flag, I'm screwed. I propose a hook styled after Py_AtExit(func) called Py_AtInit(func) which maintains a list of functions that are called in Py_Initialize right after main and site initializations. If the hook isn't used, then the cost is a single extra function call at initialization. Here's a spurious example: A customer wants a version of python that has all the math functions and his extensions to act like builtins... I would write (without refcnt or error checks ;-): #include "Python.h" static void after_init(void) { PyObject *builtin,*builtin_dict,*math,*math_dict,*user,*user_dict; builtin = PyImport_ImportModule("__builtin__"); builtin_dict = PyModule_GetDict(builtin); math = PyImport_ImportModule("math"); math_dict = PyModule_GetDict(math); user = PyImport_ImportModule("user"); user_dict = PyModule_GetDict(math); PyDict_Update(builtin_dictionary, math_dict); PyDict_Update(builtin_dictionary, user_dict); } int main(int argc, char** argv) { PyImport_AppendInittab("user",inituser); Py_AtInit(after_init); return Py_Main(argc, argv); } voila! An extended Python with new builtins. I actually want this to do some MPI initialization to setup a single user prompt with broadcast which has to run after Py_Initialize() but before the import of readline. I've attached a copy of the patch (also going to patches at sf.net) Pat -- Patrick Miller | (925) 423-0309 | http://www.llnl.gov/CASC/people/pmiller Son, when you grow up you will know who I really am. I am just a child like you who has been forced to act responsibly. -- Rod Byrnes Index: dist/src/Include/pythonrun.h =================================================================== RCS file: /cvsroot/python/python/dist/src/Include/pythonrun.h,v retrieving revision 2.62 diff -c -r2.62 pythonrun.h *** dist/src/Include/pythonrun.h 13 Feb 2003 22:07:52 -0000 2.62 --- dist/src/Include/pythonrun.h 30 Apr 2003 22:04:13 -0000 *************** *** 75,80 **** --- 75,81 ---- PyAPI_FUNC(void) PyErr_Display(PyObject *, PyObject *, PyObject *); PyAPI_FUNC(int) Py_AtExit(void (*func)(void)); + PyAPI_FUNC(int) Py_AtInit(void (*func)(void)); PyAPI_FUNC(void) Py_Exit(int); Index: dist/src/Python/pythonrun.c =================================================================== RCS file: /cvsroot/python/python/dist/src/Python/pythonrun.c,v retrieving revision 2.193 diff -c -r2.193 pythonrun.c *** dist/src/Python/pythonrun.c 22 Apr 2003 11:18:00 -0000 2.193 --- dist/src/Python/pythonrun.c 30 Apr 2003 22:04:16 -0000 *************** *** 106,111 **** --- 106,135 ---- return flag; } + #define NINITFUNCS 32 + static void (*initfuncs[NINITFUNCS])(void); + static int ninitfuncs = 0; + + int Py_AtInit(void (*func)(void)) + { + if (ninitfuncs >= NINITFUNCS) + return -1; + if (!func) + return -1; + initfuncs[ninitfuncs++] = func; + return 0; + } + + static void initinitialize(void) + { + int i; + for(i=0;i<ninitfuncs;++i) { + initfuncs[i](); + if (PyErr_Occurred()) + Py_FatalError("Py_AtInit: initialization error"); + } + } + void Py_Initialize(void) { *************** *** 182,190 **** --- 206,217 ---- initsigs(); /* Signal handling stuff, including initintr() */ initmain(); /* Module __main__ */ + if (!Py_NoSiteFlag) initsite(); /* Module site */ + initinitialize(); /* Extenstion hooks */ + /* auto-thread-state API, if available */ #ifdef WITH_THREAD _PyGILState_Init(interp, tstate); *************** *** 1418,1423 **** --- 1445,1451 ---- #endif /* MS_WINDOWS */ abort(); } + /* Clean up and exit */

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