Mailman 3 July 2004 - 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:

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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.

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mimetypes and _winreg
by Mike Brown 02 Feb '05

02 Feb '05

I thought it would be nice to try to improve the mimetypes module by having it, on Windows, query the Registry to get the mapping of filename extensions to media types, since the mimetypes code currently just blindly checks posix-specific paths for httpd-style mapping files. However, it seems that the way to get mappings from the Windows registry is excessively slow in Python. I'm told that the reason has to do with the limited subset of APIs that are exposed in the _winreg module. I think it is that EnumKey(key, index) is querying for the entire list of subkeys for the given key every time you call it. Or something. Whatever the situation is, the code I tried below is way slower than I think it ought to be. Does anyone have any suggestions (besides "write it in C")? Could _winreg possibly be improved to provide an iterator or better interface to get the subkeys? (or certain ones? There are a lot of keys under HKEY_CLASSES_ROOT, and I only need the ones that start with a period). Should I file this as a feature request? Thanks -Mike from _winreg import HKEY_CLASSES_ROOT, OpenKey, EnumKey, QueryValueEx i = 0 typemap = {} try: while 1: subkeyname = EnumKey(HKEY_CLASSES_ROOT, i) try: subkey = OpenKey(HKEY_CLASSES_ROOT, subkeyname) if subkeyname[:1] == '.': data = QueryValueEx(subkey, 'Content Type')[0] print subkeyname, '=', data typemap[subkeyname] = data # data will be unicode except EnvironmentError, WindowsError: pass i += 1 except WindowsError: pass

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Decoding incomplete unicode
by Walter Dörwald 26 Aug '04

26 Aug '04

Pythons unicode machinery currently has problems when decoding incomplete input. When codecs.StreamReader.read() encounters a decoding error it reads more bytes from the input stream and retries decoding. This is broken for two reasons: 1) The error might be due to a malformed byte sequence in the input, a problem that can't be fixed by reading more bytes. 2) There may be no more bytes available at this time. Once more data is available decoding can't continue because bytes from the input stream have already been read and thrown away. (sio.DecodingInputFilter has the same problems) I've uploaded a patch that fixes these problems to SF: http://www.python.org/sf/998993 The patch implements a few additional features: - read() has an additional argument chars that can be used to specify the number of characters that should be returned. - readline() is supported on all readers derived from codecs.StreamReader(). - readline() and readlines() have an additional option for dropping the u"\n". The patch is still missing changes to the escape codecs ("unicode_escape" and "raw_unicode_escape") and I haven't touched the CJK codecs, but it has test cases that check the new functionality for all affected codecs (UTF-7, UTF-8, UTF-16, UTF-16-LE, UTF-16-BE). Could someone take a look at the patch? Bye, Walter Dörwald

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New Subscriber
by Dave Hastings 12 Aug '04

12 Aug '04

Hello fellow developers. My name is David Hastings and I am a new subscriber to the python-dev list. I'm also a little new to python but I can get around in it. I have been learning how to use the language for about a year now. First, some information about myself. I am a senior attending the University of Minnesota. Today was the last day of classes for the spring semester and also the last day of my college career. I am receiving a Bachelor of Science in Computer Science degree. Man it feels good to be done ! This last semester a friend (Michael Sampson) and I took an independent study class where we sign up with a Professor and decide on a project and work on it until the end of the semester. The project that was decided upon, with the advice of the Professor, was to make a CGIpm python module that reflected CGI.pm for perl. We noticed that there is a current cgi module for python and even a cgipm module. These modules are very useful, but did not include all the functions that CGI.pm for perl provides. It turns out that my Professor really likes python and would have loved to see a CGIpm python module for python that was like the CGI.pm module for perl. (I think he is a bit turned off by perl, more because it is a language that is not that easy to pick up unless you are familiar with unix, namely sed and awk.) We decided to take the oportunity and wrote CGIpm.py. I'm not going to go into a lot of details in this e-mail since it is an introductory e-mail, but the first version of CGIpm.py is complete. I feel that this e-mail is a bit long winded as is, so I think I will end it. I can not wait to start reading about all the new ideas, development, and contributions that this list will provide. Dave

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Would like to add Edward Loper as a Python developer
by Tim Peters 06 Aug '04

06 Aug '04

Edward Loper runs the Natural Language Toolkit project on SF: http://nltk.sourceforge.net/ and the Epydoc project: http://epydoc.sourceforge.net/ More importantly <wink>, he's a heavy doctest user and has lots of ideas for improving it. doctest's implementation has grown unwieldy, and is in need of refactoring. Jim (Fulton), Edward and I intend to do a lot there over the coming two weeks, and giving Edward commit privileges would simplify and speed the process. This is intended to be limited to doctest changes. Are there objections? If anyone else is interested in contributing to doctest surgery, let me know. A Wiki area might be a decent way to coordinate. Ideas already on the table include restructuring for plugability (e.g., there's no sane way for you to take over doctest error reporting now, but restructuring to do much more via (overridable) class methods is a sane alternative); new gimmicks like notation for "there's a blank line here in this expected output"; a sane way to get into the debugger upon a doctest failure (right now, if you try, doctest is still swallowing stdout, so you can't see what you're doing! Jeremy did some quick hacks around that for Zope3 already); better support for writing "whole file" doctests (tutorial narratives liberally illustrated with Python examples -- Zope3 is finding these very helpful); and documenting all the additions that snuck into Python 2.3.

5 5

Fix import errors to have data
by Jim Fulton 04 Aug '04

04 Aug '04

A common idiom to optionally support some module if it is present is to use ImportError handlers: try: import foo except ImportError: # Configure for absense of foo ... else: # Configure for presense of foo ... Unfortunately, this is a bug trap. The module foo might be present and yet it's import could fail with an import error. This can happen if one of *its* imports fails. Code like that above will hide such bugs. Unfortunately, it's hard to do this correctly, because ImportErrors don't have the module name as data. When the import error is raised, it is raised with an error message rather than data. This is because most standard exception classes share a common __str__ that simply prints their initialization arguments. At present, to conditionally support a module, you have to use code like: try: import foo except ImportError, v: if not str(v).endsswith(' foo'): raise # Configure for absense of foo ... else: # Configure for presense of foo ... which is ugly and brittle. I'd like to get this fixed. I propose to: - Provide ImportError with an __init__ that takes a module name and sets a module_name attribute - Provide ImportError with an __str__ that produces the message we have now - Change standard code that raises import errors to provide just the module name. With this change, one could write careful conditional import code like this: try: import foo except ImportError, v: if v.module_name != 'foo': raise # Configure for absense of foo ... else: # Configure for presense of foo ... which is much cleaner IMO. Jim -- Jim Fulton mailto:jim@zope.com Python Powered! CTO (540) 361-1714 http://www.python.org Zope Corporation http://www.zope.com http://www.zope.org

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RE: [Python-Dev] Fix import errors to have data
by Delaney, Timothy C (Timothy) 03 Aug '04

03 Aug '04

Tim Peters wrote: > [Delaney, Timothy C (Timothy)] >> OK - the problem as I see it is that a given module that exists, but >> raises ImportError, only raises ImportError *once*, whereas it really >> should raise ImportError every time > > Jim's after something different, while the problem you're thinking > about is more general than just ImportError. When an import of an > existing module fails for *any* reason, subsequent attempts to import > the same module succeed. For example, Good point. This is the same as not wanting modules in an insane state in sys.modules. I've just gone back over Jim's original email, and it is a different case being talked about there - specifically, determining if an ImportError was thrown by the module that was specifically being imported, rather than something it imports. However, I don't see the utility of that. I definitely can't think of a use case for it. OTOH, ensuring that if *any* exception is thrown when importing a module, it will not appear in sys.modules (and the exception is raised each time you try to import) is IMO a very useful property, and I think would solve what I think is Jim's issue at the root. Tim Delaney

7 21

Optik 1.5 in Python 2.4
by Greg Ward 02 Aug '04

02 Aug '04

Hope I'm not too late to get Optik 1.5 into Python 2.4. I release Optik 1.5a1 last weekend and so far haven't heard a peep of complaint. Sneaking it into Python 2.4a2 would help ferret out any compatibility bugs. (The changes are pretty small; the only reason I called it Optik 1.5 instead of 1.4.2 is because there are a bunch of small changes, and it's over a year since 1.4.1. ;-) The only catch is that I've updated the Optik reStructuredText docs, and haven't yet devised a clever way to convert them to LaTeX-for-the- Python-manual format (talking about optparse rather than Optik). (Code donations welcome. ;-) So: I'd like to checkin Optik 1.5a1 as optparse.py right now, and worry about the docs later. Hopefully before Python 2.4a2 goes out the door, but no promises. Objections? If I don't hear any soon, I'll do the deed tomorrow morning. Greg -- Greg Ward <gward(a)python.net> http://www.gerg.ca/ Everybody is going somewhere!! It's probably a garage sale or a disaster Movie!!

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RE: [Python-Dev] Fix import errors to have data
by Delaney, Timothy C (Timothy) 01 Aug '04

01 Aug '04

Guido van Rossum wrote: >> Then you're proposing a way for a highly knowledgable user to >> anticipate, and partially worm around, that Python leaves behind >> insane module objects in sys.modules. Wouldn't it be better to >> change Python to stop leaving insane module objects in sys.modules >> to begin with? That's harder, but seems to me it would do a lot >> more good for a lot more people. > > +1 OK - the problem as I see it is that a given module that exists, but raises ImportError, only raises ImportError *once*, whereas it really should raise ImportError every time i.e. currently doing the following: # a.py raise ImportError # b.py try: import a except ImportError: import a print 'OK' prints when it really should raise ImportError. Additionally, a module could have messed with sys.modules directly, so just putting None in for the broken module wouldn't be sufficient (you could possibly get the broken module via another name). Perhaps the import machinery could keep a (weak?) mapping from module *object* to the ImportError it raised. If the module that would be returned by the import is in the mapping, raise the corresponding ImportError instead. The appropriate line, etc in the module would thus be shown each time the module was imported. I believe this would work properly for reload() as well. Tim Delaney

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Python-Dev July 2004