Mailman 3 July 2010 - Python-Dev

PEP 1, PEP Purpose and Guidelines
by barry＠zope.com May 18, 2021

May 18, 2021

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 Aug. 14, 2014

Aug. 14, 2014

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 Dec. 25, 2012

Dec. 25, 2012

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 Feb. 8, 2011

Feb. 8, 2011

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

Problems with hex-conversion functions
by Ender Wiggin Oct. 2, 2010

Oct. 2, 2010

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

versioned .so files for Python 3.2
by Barry Warsaw Sept. 12, 2010

Sept. 12, 2010

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

22 96

Thoughts fresh after EuroPython
by Guido van Rossum Sept. 8, 2010

Sept. 8, 2010

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 Sept. 3, 2010

Sept. 3, 2010

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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logging package vs unicode
by Chris Withers Aug. 3, 2010

Aug. 3, 2010

Hi All, The documentation for the logging package doesn't include any mention of unicode. What's the recommended usage in terms of passing unicode vs encoded strings? How does this differ from Python 2 to Python 3? cheers, Chris -- Simplistix - Content Management, Batch Processing & Python Consulting - http://www.simplistix.co.uk

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proto-pep: plugin proposal (for unittest)
by Michael Foord Aug. 2, 2010

Aug. 2, 2010

Hello all, My apologies in advance if email mangles whitespace in the code examples. I can reformulate as a PEP if that is deemed useful and this document can be found online at: http://hg.python.org/unittest2/file/tip/description.txt (Please excuse errors and omissions - but do feel free to point them out.) This is a description, and request for feedback, of the unittest plugin system that I am currently prototyping in the plugins branch of unittest2_. My goal is to merge the plugin system back into unittest itself in Python 3.2. .. _unittest2: http://hg.python.org/unittest2 As part of the prototype I have been implementing some example plugins (in unittest2/plugins/) so I can develop the mechanism against real rather than imagined use cases. Jason Pellerin, creator of nose, has been providing me with feedback and has been trying it out by porting some of the nose plugins to unittest [#]_. He comments on the system "it looks very flexible and clean". ;-) Example plugins available and included: * a pep8 and pyflakes checker * a debugger plugin that drops you into pdb on test fail / error * a doctest loader (looks for doctests in all text files in the project) * use a regex for matching files in test discovery instead of a glob * growl notifications on test run start and stop * filter individual *test methods* using a regex * load test functions from modules as well as TestCases * integration with the coverage module for coverage reporting In addition I intend to create a plugin that outputs junit compatible xml from a test run (for integration with tools like the hudson continuous integration server) and a test runner that runs tests in parallel using multiprocessing. Not all of these will be included in the merge to unittest. Which ones will is still an open question. I'd like feedback on the proposal, and hopefully approval to port it into unittest after discussion / amendment / completion. In particular I'd like feedback on the basic system, plus which events should be available and what information should be available in them. Note that the system is *not* complete in the prototype. Enough is implemented to get "the general idea" and to formalise the full system. It still needs extensive tests and the extra work in TestProgram makes it abundantly clear that refactoring there is well overdue... In the details below open questions and todos are noted. I *really* value feedback (but will ignore bikeshedding ;-) .. note:: Throughout this document I refer to the prototype implementation using names like ``unittest2.events.hooks``. Should this proposal be accepted then the names will live in the unittest package instead of unittest2. The core classes for the event system live in the current implementation in the ``unittest2.events`` namespace. Abstract ======== unittest lacks a standard way of extending it to provide commonly requested functionality, other than subclassing and overriding (and reimplementing) parts of its behaviour. This document describes a plugin system already partially prototyped in unittest2. Aspects of the plugin system include: * an events mechanism where handlers can be registered and called during a test run * a Plugin class built over the top of this for easy creation of plugins * a configuration system for specifying which plugins should be loaded and for configuring individual plugins * command line integration * the specific set of events and the information / actions available to them As the plugin system essentially just adds event calls to key places it has few backwards compatibility issues. Unfortunately existing extensions that override the parts of unittest that call these events will not be compatible with plugins that use them. Framework authors who re-implement parts of unittest, for example custom test runners, may want to add calling these events in appropriate places. Rationale ========= Why a plugin system for unittest? unittest is the standard library test framework for Python but in recent years has been eclipsed in functionality by frameworks like nose and py.test. Among the reasons for this is that these frameworks are easier to extend with plugins than unittest. unittest makes itself particularly difficult to extend by using subclassing as its basic extension mechanism. You subclass and override behaviour in its core classes like the loader, runner and result classes. This means that where you have more than one "extension" working in the same area it is very hard for them to work together. Whilst various extensions to unittest do exist (e.g. testtools, zope.testrunner etc) they don't tend to work well together. In contrast the plugin system makes creating extensions to unittest much simpler and less likely that extensions will clash with each other. nose itself exists as a large system built over the top of unittest. Extending unittest in this way was very painful for the creators of nose, and every release of Python breaks nose in some way due to changes in unittest. One of the goals of the extension mechanism is to allow nose2 to be a much thinner set of plugins over unittest(2) that is much simpler to maintain [#]_. The early indications are that the proposed system is a good fit for this goal. Low Level Mechanism ==================== The basic mechanism is having events fired at various points during a test run. Plugins can register event handler functions that will be called with an event object. Multiple functions may be registered to handle an event and event handlers can also be removed. Over the top of this is a ``Plugin`` class that simplifies building plugins on top of this mechanism. This is described in a separate section. The events live on the ``unittest2.events.hooks`` class. Handlers are added using ``+=`` and removed using ``-=``, a syntax borrowed from the .NET system. For example adding a handler for the ``startTestRun`` event:: from unittest2.events import hooks def startTestRun(event): print 'test run started at %s' % event.startTime hooks.startTestRun += startTestRun Handlers are called with an Event object specific to the event. Each event provides different information on its event objects as attributes. For example the attributes available on ``StartTestRunEvent`` objects are: * ``suite`` - the test suite for the full test run * ``runner`` - the test runner * ``result`` - the test result * ``startTime`` The name of events, whether any should be added or removed, and what information is available on the event objects are all valid topics for discussion. Specific events and the information available to them is covered in a section below. An example plugin using events directly is the ``doctestloader`` plugin. Framework authors who re-implement parts of unittest, for example custom test runners, may want to add calling these events in appropriate places. This is very simple. For example the ``pluginsLoaded`` event is fired with a ``PluginsLoadedEvent`` object that is instantiated without parameters:: from unittest2.events import hooks, PluginsLoadedEvent hooks.pluginsLoaded(PluginsLoadedEvent()) Why use event objects and not function parameters? -------------------------------------------------- There are several reasons to use event objects instead of function parameters. The *disadvantage* of this is that the information available to an event is not obvious from the signature of a handler. There are several compelling advantages however: * the signature of all handler functions is identical and therefore easy to remember * backwards compatibility - new attributes can be added to event objects (and parameters deprecated) without breaking existing plugins. Changing the way a function is called (unless all handlers have a ``**kw`` signature) is much harder. * several of the events have a lot of information available. This would make the signature of handlers huge. With an event object handlers only need to be aware of attributes they are interested in and ignore information they aren't interested in ("only pay for what you eat"). * some of the attributes are mutable - the event object is shared between all handlers, this would be less obvious if function parameters were used * calling multiple handlers and still returning a value (see the handled pattern below) The handled pattern -------------------- Several events can be used to *override* the default behaviour. For example the 'matchregexp' plugin uses the ``matchPath`` event to replace the default way of matching files for loading as tests during test discovery. The handler signals that it is handling this event, and the default implementation should not be run, by setting ``event.handled = True``:: def matchRegexp(event): pattern = event.pattern name = event.name event.handled = True path = event.path if matchFullPath: return re.match(pattern, path) return re.match(pattern, name) Where the default implementation returns a value, for example creating a test suite, or in the case of ``matchPath`` deciding if a path matches a file that should be loaded as a test, the handler can return a result. If an event sets handled on an event then no more handlers will be called for that event. Which events can be handled, and which not, is discussed in the events section. The Plugin Class ================ A sometimes-more-convenient way of creating plugins is to subclass the ``unittest2.events.Plugin`` class. By default subclassing ``Plugin`` will auto-instantiate the plugin and store the instance in a list of loaded plugins. Each plugin has a ``register()`` method that auto-hooks up all methods whose names correspond to events. Plugin classes may also provide ``configSection`` and ``commandLineSwitch`` class attributes which simplifies enabling the plugin through the command line and making available a section from the configuration file(s). A simple plugin using this is the 'debugger' plugin that starts ``pdb`` when the ``onTestFail`` event fires:: from unittest2.events import Plugin import pdb import sys class Debugger(Plugin): configSection = 'debugger' commandLineSwitch = ('D', 'debugger', 'Enter pdb on test fail or error') def __init__(self): self.errorsOnly = self.config.as_bool('errors-only', default=False) def onTestFail(self, event): value, tb = event.exc_info[1:] test = event.test if self.errorsOnly and isinstance(value, test.failureException): return original = sys.stdout sys.stdout = sys.__stdout__ try: pdb.post_mortem(tb) finally: sys.stdout = original A plugin that doesn't want to be auto-instantiated (for example a base class used for several plugins) can set ``autoCreate = False`` as a class attribute. (This attribute is only looked for on the class directly and so isn't inherited by subclasses.) If a plugin is auto-instantiated then the instance will be set as the ``instance`` attribute on the plugin class. ``configSection`` and ``commandLineSwitch`` are described in the `configuration system`_ and `command line integration`_ sections. Plugin instances also have an ``unregister`` method that unhooks all events. It doesn't exactly correspond to the ``register`` method (it undoes some of the work done when a plugin is instantiated) and so can only be called once. Plugins to be loaded are specified in configuration files. For frameworks not using the unittest test runner and configuration system APIs for loading plugins are available in the form of the ``loadPlugins`` function (which uses the configuration system to load plugins) and ``loadPlugin`` which loads an individual plugin by module name. Loading plugins just means importing the module containing the plugin. Configuration system ==================== By default the unittest2 test runner (triggered by the unit2 script or for unittest ``python -m unittest``) loads two configuration files to determine which plugins to load. A user configuration file, ~/unittest.cfg (alternative name and location would be possible), can specify plugins that will always be loaded. A per-project configuration file, unittest.cfg which should be located in the current directory when unit2 is launched, can specify plugins for individual projects. To support this system several command line options have been added to the test runner:: --config=CONFIGLOCATIONS Specify local config file location --no-user-config Don't use user config file --no-plugins Disable all plugins Several config files can be specified using ``--config``. If the user config is being loaded then it will be loaded first (if it exists), followed by the project config (if it exists) *or* any config files specified by ``--config``. ``--config`` can point to specific files, or to a directory containing a ``unittest.cfg``. Config files loaded later are merged into already loaded ones. Where a *key* is in both the later key overrides the earlier one. Where a section is in both but with different keys they are merged. (The exception to keys overriding is the 'plugins' key in the unittest section - these are combined to create a full list of plugins. Perhaps multiline values in config files could also be merged?) plugins to be loaded are specified in the ``plugins`` key of the ``unittest`` section:: [unittest] plugins = unittest2.plugins.checker unittest2.plugins.doctestloader unittest2.plugins.matchregexp unittest2.plugins.moduleloading unittest2.plugins.debugger unittest2.plugins.testcoverage unittest2.plugins.growl unittest2.plugins.filtertests The plugins are simply module names. They either hook themselves up manually on import or are created by virtue of subclassing ``Plugin``. A list of all loaded plugins is available as ``unittest2.events.loadedPlugins`` (a list of strings). For accessing config values there is a ``getConfig(sectionName=None)`` function. By default it returns the whole config data-structure but it an also return individual sections by name. If the section doesn't exist an empty section will be returned. The config data-structure is not read-only but there is no mechanism for persisting changes. The config is a dictionary of ``Section`` objects, where a section is a dictionary subclass with some convenience methods for accessing values:: section = getConfig(sectionName) integer = section.as_int('foo', default=3) number = section.as_float('bar', default=0.0) # as_list returns a list with empty lines and comment lines removed items = section.as_list('items', default=[]) # as_bool allows 'true', '1', 'on', 'yes' for True (matched case-insensitively) and # 'false', 'off', '0', 'no', '' for False value = section.as_bool('value', default=True) If a plugin specifies a ``configSection`` as a class attribute then that section will be fetched and set as the ``config`` attribute on instances. By convention plugins should use the 'always-on' key in their config section to specify that the plugin should be switched on by default. If 'always-on' exists and is set to 'True' then the ``register()`` method will be called on the plugin to hook up all events. If you don't want a plugin to be auto-registered you should fetch the config section yourself rather than using ``configSection``. If the plugin is configured to be 'always-on', and is auto-registered, then it doesn't need a command line switch to turn it on (although it may add other command line switches or options) and ``commandLineSwitch`` will be ignored. Command Line Interface ====================== Plugins may add command line options, either switches with a callback function or options that take values and will be added to a list. There are two functions that do this: ``unittest2.events.addOption`` and ``unittest2.events.addDiscoveryOption``. Some of the events are only applicable to test discovery (``matchPath`` is the only one currently I think), options that use these events should use ``addDiscoveryOption`` which will only be used if test discovery is invoked. Both functions have the same signature:: addDiscoveryOption(callback, opt=None, longOpt=None, help=None) addOption(plugin.method, 'X', '--extreme', 'Run tests in extreme mode') * ``callback`` is a callback function (taking no arguments) to be invoked if the option is on *or* a list indicating that this is an option that takes arguments, values passed in at the command line will be added to the list * ``opt`` is a short option for the command (or None) not including the leading '-' * ``longopt`` a long option for the command (or None) not including the leading '--' * ``help`` is optional help text for the option, to be displayed by ``unit2 -h`` Lowercase short options are reserved for use by unittest2 internally. Plugins may only add uppercase short options. If a plugin needs a simple command line switch (on/off) then it can set the ``commandLineSwitch`` class attribute to a tuple of ``(opt, longOpt, help)``. The ``register()`` method will be used as the callback function, automatically hooking the plugin up to events if it is switched on. The Events ========== This section details the events implemented so far, the order they are called in, what attributes are available on the event objects, whether the event is 'handleable' (and what that means for the event), plus the intended use case for the event. Events in rough order are: * ``pluginsLoaded`` * ``handleFile`` * ``matchPath`` * ``loadTestsFromNames`` * ``loadTestsFromName`` * ``loadTestsFromModule`` * ``loadTestsFromTestCase`` * ``getTestCaseNames`` * ``runnerCreated`` * ``startTestRun`` * ``startTest`` * ``onTestFail`` * ``stopTest`` * ``stopTestRun`` pluginsLoaded ------------- This event is useful for plugin initialisation. It is fired after all plugins have been loaded, the config file has been read and command line options processed. The ``PluginsLoadedEvent`` has one attribute: ``loadedPlugins`` which is a list of strings referring to all plugin modules that have been loaded. handleFile ---------- This event is fired when a file is looked at in test discovery or a *filename* is passed at the command line. It can be used for loading tests from non-Python files, like doctests from text files, or adding tests for a file like pep8 and pyflakes checks. A ``HandleFileEvent`` object has the following attributes: * ``extraTests`` - a list, extend this with tests to *add* tests that will be loaded from this file without preventing the default test loading * ``name`` - the name of the file * ``path`` - the full path of the file being looked at * ``loader`` - the ``TestLoader`` in use * ``pattern`` - the pattern being used to match files, or None if not called during test discovery * ``top_level_directory`` - the top level directory of the project tests are being loaded from, or the current working directory if not called during test discovery This event *can* be handled. If it is handled then the handler should return a test suite or None. Returning None means no tests will be loaded from this file. If any plugin has created any ``extraTests`` then these will be used even if a handler handles the event and returns None. If this event is not handled then it will be matched against the pattern (test discovery only) and either be rejected or go through for standard test loading. matchPath --------- ``matchPath`` is called to determine if a file should be loaded as a test module. This event only fires during test discovery. ``matchPath`` is only fired if the filename can be converted to a valid python module name, this is because tests are loaded by importing. If you want to load tests from files whose paths don't translate to valid python identifiers then you should use ``handleFile`` instead. A ``MatchPathEvent`` has the following attributes: * ``path`` - full path to the file * ``name`` - filename only * ``pattern`` - pattern being used for discovery This event *can* be handled. If it is handled then the handler should return True or False to indicate whether or not test loading should be attempted from this file. If this event is not handled then the pattern supplied to test discovery will be used as a glob pattern to match the filename. loadTestsFromNames ------------------ This event is fired when ``TestLoader.loadTestsFromNames`` is called. Attributes on the ``LoadFromNamesEvent`` object are: * ``loader`` - the test loader * ``names`` - a list of the names being loaded * ``module`` - the module passed to ``loader.loadTestsFromNames(...)`` * ``extraTests`` - a list of extra tests to be added to the suites loaded from the names This event can be handled. If it is handled then the handler should return a list of suites or None. Returning None means no tests will be loaded from these names. If any plugin has created any ``extraTests`` then these will be used even if a handler handles the event and returns None. If this event is not handled then ``loader.loadTestFromName`` will be called for each name to build up the list of suites. loadTestsFromName ----------------- This event is fired when ``TestLoader.loadTestsFromName`` is called. Attributes on the ``LoadFromNameEvent`` object are: * ``loader`` - the test loader * ``name`` - the name being loaded * ``module`` - the module passed to ``loader.loadTestsFromName(...)`` * ``extraTests`` - a suite of extra tests to be added to the suite loaded from the name This event can be handled. If it is handled then the handler should return a TestSuite or None. Returning None means no tests will be loaded from this name. If any plugin has created any ``extraTests`` then these will be used even if a handler handles the event and returns None. If the event is not handled then each name will be resolved and tests loaded from it, which may mean calling ``loader.loadTestsFromModule`` or ``loader.loadTestsFromTestCase``. loadTestsFromModule ------------------- This event is fired when ``TestLoader.loadTestsFromModule`` is called. It can be used to customise the loading of tests from a module, for example loading tests from functions as well as from TestCase classes. Attributes on the ``LoadFromModuleEvent`` object are: * ``loader`` - the test loader * ``module`` - the module object tests * ``extraTests`` - a suite of extra tests to be added to the suite loaded from the module This event can be handled. If it is handled then the handler should return a TestSuite or None. Returning None means no tests will be loaded from this module. If any plugin has created any ``extraTests`` then these will be used even if a handler handles the event and returns None. If the event is not handled then ``loader.loadTestsFromTestCase`` will be called for every TestCase in the module. Event if the event is handled, if the module defines a ``load_tests`` function then it *will* be called for the module. This removes the responsibility for implementing the ``load_tests`` protocol from plugin authors. loadTestsFromTestCase --------------------- This event is fired when ``TestLoader.loadTestsFromTestCase`` is called. It could be used to customise the loading of tests from a TestCase, for example loading tests with an alternative prefix or created generative / parameterized tests. Attributes on the ``LoadFromTestCaseEvent`` object are: * ``loader`` - the test loader * ``testCase`` - the test case class being loaded * ``extraTests`` - a suite of extra tests to be added to the suite loaded from the TestCase This event can be handled. If it is handled then the handler should return a TestSuite or None. Returning None means no tests will be loaded from this module. If any plugin has created any ``extraTests`` then these will be used even if a handler handles the event and returns None If the event is not handled then ``loader.getTestCaseNames`` will be called to get method names from the test case and a suite will be created by instantiating the TestCase class with each name it returns. getTestCaseNames ---------------- This event is fired when ``TestLoader.getTestCaseNames`` is called. It could be used to customise the method names used to load tests from a TestCase, for example loading tests with an alternative prefix from the default or filtering for specific names. Attributes on the ``GetTestCaseNamesEvent`` object are: * ``loader`` - the test loader * ``testCase`` - the test case class that tests are being loaded from * ``testMethodPrefix`` - set to None, modify this attribute to *change* the prefix being used for this class * ``extraNames`` - a list of extra names to use for this test case as well as the default ones * ``excludedNames`` - a list of names to exclude from loading from this class This event can be handled. If it is handled it should return a list of strings. Note that if this event returns an empty list (or None which will be replaced with an empty list then ``loadTestsFromTestCase`` will still check to see if the TestCase has a ``runTest`` method. Even if the event is handled ``extraNames`` will still be added to the list, however *excludedNames`` won't be removed as they are filtered out by the default implementation which looks for all attributes that are methods (or callable) whose name begins with ``loader.testMethodPrefix`` (or ``event.testMethodPrefix`` if that is set) and aren't in the list of excluded names (converted to a set first for efficient lookup). The list of names will also be sorted using ``loader.sortTestMethodsUsing``. runnerCreated ------------- This event is fired when the ``TextTestRunner`` is instantiated. It can be used to customize the test runner, for example replace the stream and result class, without needing to write a custom test harness. This should allow the default test runner script (``unit2`` or ``python -m untitest``) to be suitable for a greater range of projects. Projects that want to use custom test reporting should be able to do it through a plugin rather than having to rebuild the runner and result machinery, which also requires writing custom test collection too. The ``RunnerCreatedEvent`` object only has one attribute; ``runner`` which is the runner instance. startTestRun ------------ This event is fired when the test run is started. This is used, for example, by the growl notifier that displays a growl notification when a test run begins. It can also be used for filtering tests after they have all been loaded or for taking over the test run machinery altogether, for distributed testing for example. The ``StartTestRunEvent`` object has the following attributes: * ``test`` - the full suite of all tests to be run (may be modified in place) * ``result`` - the result object * ``startTime`` - the time the test run started Currently this event can be handled. This prevents the normal test run from executing, allowing an alternative implementation, but the return value is unused. Handling this event (as with handling any event) prevents other plugins from executing. This means that the it wouldn't be possible to safely combine a distributed test runner with a plugin that filters the suite. Fixing this issue is one of the open issues with the plugin system. startTest --------- This event is fired immediately before a test is executed (inside ``TestCase.run(...)``). The ``StartTestEvent`` object has the following attributes: * ``test`` - the test to be run * ``result`` - the result object * ``startTime`` - the time the test starts execution This event cannot be handled. onTestFail ---------- This event is fired when a test setUp, a test, a tearDown or a cleanUp fails or errors. It is currently used by the debugger plugin. It is *not* currently called for 'internal' unittest exceptions like ``SkipTest`` or expected failures and unexpected successes. Attributes on the ``TestFailEvent`` are: * ``test`` - the test * ``result`` - the result * ``exc_info`` - the result of ``sys.exc_info()`` after the error / fail * ``when`` - one of 'setUp', 'call', 'tearDown', or 'cleanUp' This event cannot be handled. Should this event be able to suppress raised exceptions? It should also be able to modify the traceback so that bare asserts could be used but still provide useful diagnostic information. Should this event be fired for test skips? stopTest -------- This event is fired when a test execution is completed. It includes a great deal of information about the test and could be used to completely replace test reporting, making the test result potentially obsolete. It will be used by the junit-xml plugin to generate the xml reports describing the test run. If there are errors during a tearDown or clean up functions then this event may be fired several times for a test. For each call the ``stage`` will be different, although there could be several errors during clean up functions. Attributes on the ``StopTestEvent`` are: * ``test`` - the test * ``result`` - the result * ``exc_info`` - the result of ``sys.exc_info()`` after an error / fail or None for success * ``stopTime``- time the test stopped, including tear down and clean up functions * ``timeTaken`` - total time for test execution from setUp to clean up functions * ``stage`` - one of setUp, call, tearDown, cleanUp, or None for success * ``outcome`` - one of passed, failed, error, skipped, unexpectedSuccess, expectedFailure The outcomes all correspond to an attribute that will be set to True or False depending on outcome: * ``passed`` * ``failed`` * ``error`` * ``skipped`` * ``unexpectedSuccess`` * ``expectedFailure`` In addition there is a ``skipReason`` that will be None unless the test was skipped, in which case it will be a string containing the reason. This event cannot be handled. stopTestRun ----------- This event is fired when the test run completes. It is useful for reporting tools. The ``StopTestRunEvent`` event objects have the following attributes: * ``runner`` - the test runner * ``result`` - the test result * ``stopTime`` - the time the test run completes * ``timeTaken`` - total time taken by the test run

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