Python-Dev May 2003

python-dev@python.org

108 participants
140 discussions

RE: [Python-Dev] Those import related syntax errors again...

by Samuele Pedroni

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.

15 years, 8 months

2.3b1 release

by Guido van Rossum

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

17 years, 2 months

doctest extensions

by Jim Fulton

I've written some doctest extensions to: - Generate a unitest (pyunit) test suite from a module with doctest tests. Each doc string containing one or more doctest tests becomes a test case. If a test fails, an error message is included in the unittest output that has the module file name and the approximate line number of the docstring containing the failed test formatted in a way understood by emacs error parsing. This is important. ;) - Debug doctest tests. Normally, doctest tests can't be debugged with pdb because, while they are running, doctest has taken over standard output. This tool extracts the tests in a doc string into a separate script and runs pdb on it. - Extract a doctest doc string into a script file. I think that these would be good additions to doctest and propose to add them, The current source can be found here: http://cvs.zope.org/Zope3/src/zope/testing/doctestunit.py?rev=HEAD&content-… I ended up using a slightly different (and simpler) strategy for finding docstrings than doctest uses. This might be an issue. Jim -- Jim Fulton mailto:jim@zope.com Python Powered! CTO (703) 361-1714 http://www.python.org Zope Corporation http://www.zope.com http://www.zope.org

17 years, 3 months

Change to ossaudiodev setparameters() method

by Greg Ward

Currently, oss_audio_device objects have a setparameters() method with a rather silly interface: oss.setparameters(sample_rate, sample_size, num_channels, format [, emulate]) This is silly because 1) 'sample_size' is implicit in 'format', and 2) the implementation doesn't actually *use* sample_size for anything -- it just checks that you have passed in the correct sample size, ie. if you specify an 8-bit format, you must pass sample_size=8. (This is code inherited from linuxaudiodev that I never got around to cleaning up.) In addition to being silly, this is not the documented interface. The docs don't mention the 'sample_size' argument at all. Presumably the doc writer realized the silliness and was going to pester me to remove 'sample_size', but never got around to it. (Lot of that going around.) So, even though we're in a beta cycle, am I allowed to change the code so it's 1) sensible and 2) consistent with the documentation? Greg -- Greg Ward <gward(a)python.net> http://www.gerg.ca/ Sure, I'm paranoid... but am I paranoid ENOUGH?

17 years, 4 months

Algoritmic Complexity Attack on Python

by Scott A Crosby

Hello. We have analyzed this software to determine its vulnerability to a new class of DoS attacks that related to a recent paper. ''Denial of Service via Algorithmic Complexity Attacks.'' This paper discusses a new class of denial of service attacks that work by exploiting the difference between average case performance and worst-case performance. In an adversarial environment, the data structures used by an application may be forced to experience their worst case performance. For instance, hash tables are usually thought of as being constant time operations, but with large numbers of collisions will degrade to a linked list and may lead to a 100-10,000 times performance degradation. Because of the widespread use of hash tables, the potential for attack is extremely widespread. Fortunately, in many cases, other limits on the system limit the impact of these attacks. To be attackable, an application must have a deterministic or predictable hash function and accept untrusted input. In general, for the attack to be signifigant, the applications must be willing and able to accept hundreds to tens of thousands of 'attack inputs'. Because of that requirement, it is difficult to judge the impact of these attack without knowing the source code extremely well, and knowing all ways in which a program is used. As part of this project, I have examined python 2.3b1, and the hash function 'string_hash' is deterministic. Thus any script that may hash untrusted input may vulnerable to our attack. Furthermore, the structure of the hash functions allows our fast collision generation algorithm to work. This means that any script written in python that hashes a large number of keys from an untrusted source is potentially subject to a severe performance degradation. Depending on the application or script, this could be a critical DoS. The solution for these attacks on hash tables is to make the hash function unpredictable via a technique known as universal hashing. Universal hashing is a keyed hash function where, based on the key, one of a large set hash functions is chosen. When benchmarking, we observe that for short or medium length inputs, it is comparable in performance to simple predictable hash functions such as the ones in Python or Perl. Our paper has graphs and charts of our benchmarked performance. I highly advise using a universal hashing library, either our own or someone elses. As is historically seen, it is very easy to make silly mistakes when attempting to implement your own 'secure' algorithm. The abstract, paper, and a library implementing universal hashing is available at http://www.cs.rice.edu/~scrosby/hash/. Scott

17 years, 4 months

Introduction

by Terence Way

I've been lurking for a bit, and now seems like a good time to introduce myself. * I build messaging systems for banks, earlier I was CTO of a dot-com. * I started programming on the TRS-80 and the RCA COSMAC VIP, later on the Apple ][. * I am a Java refugee (well, I might still code in Java for pay). * I'm into formal methods. Translation: I like *talking* about formal methods, but I never use them myself :-) I read somewhere that the best way to build big Python callouses was to write a PEP. Here goes: http://www.wayforward.net/pycontract/pep-0999.html Programming by Contract for Python... pre-conditions, post-conditions, invariants, with all the Eiffel goodness like weakening pre-conditions and strengthening invariants and post-conditions on inheritance, and access to old values. All from docstrings, like doctest. I'm also into handling insane numbers of incoming connections on cheap boxes: compare Jef Poskanzer's thttpd to Apache. 10000 simultaneous HTTP connections on a $400 computer just gets me giggling. Stackless Python intrigues me greatly for the same reason. I guess that's it for now... Cheers!

17 years, 4 months

more-precise instructions for "Python.h first"?

by David Abrahams

Boost.Python is now trying hard to accomodate the "Python.h before system headers rule". Unfortunately, we still need a wrapper around Python.h, at least for some versions of Python, so that we can work around some issues like: // // Python's LongObject.h helpfully #defines ULONGLONG_MAX for us // even when it's not defined by the system which confuses Boost's // config // To cope with that correctly, we need to see <limits.h> (a system header) before longobject.h. Currently, we're including <limits.h>, then <patchlevel.h>, well, and then the wrapper gets a little complicated adjusting for various compilers. Anyway, the point is that I'd like to have the rule changed to "You have to include Python.h or xxxx.h before any system header" where xxxx.h is one of the other existing headers #included in Python.h that is responsible for setting up whatever macros cause this inclusion-order requirement in the first place (preferably not LongObject.h!) That way I might be able to get those configuration issues sorted out without violating the #inclusion order rule. What I have now seems to work, but I'd rather do the right thing (TM). -- Dave Abrahams Boost Consulting www.boost-consulting.com

17 years, 4 months

RELEASED Python 2.2.3 (final)

by Barry Warsaw

I'm happy to announce the release of Python 2.2.3 (final). This is a bug fix release for the stable Python 2.2 code line. It contains more than 40 bug fixes and memory leak patches since Python 2.2.2, and all Python 2.2 users are encouraged to upgrade. The new release is available here: http://www.python.org/2.2.3/ For full details, see the release notes at http://www.python.org/2.2.3/NEWS.txt There are a small number of minor incompatibilities with Python 2.2.2; for details see: http://www.python.org/2.2.3/bugs.html Perhaps the most important is that the Bastion.py and rexec.py modules have been disabled, since we do not deem them to be safe. As usual, a Windows installer and a Unix/Linux source tarball are made available. The documentation has been updated as well, and is available both on-line and in many different formats. At the moment, no Mac version or Linux RPMs are available, although I expect them to appear soon. On behalf of Guido, I'd like to thank everyone who contributed to this release, and who continue to ensure Python's success. Enjoy, -Barry

17 years, 4 months

KeyboardInterrupt on Windows

by Guido van Rossum

I received this problem report (Kurt is the IDLEFORK developer). Does anybody know what could be the matter here? What changed recently??? --Guido van Rossum (home page: http://www.python.org/~guido/) ------- Forwarded Message Date: Fri, 30 May 2003 15:50:15 -0400 From: kbk(a)shore.net (Kurt B. Kaiser) To: Guido van Rossum <guido(a)python.org> Subject: KeyboardInterrupt I find that while 1: pass doesn't respond to a KeyboardInterrupt on Python2.3b1 on either WinXP or W2K. Is this generally known? I couldn't find any mention of it. while 1: a = 0 is fine on 2.3b1, and both work on Python2.2. - -- KBK ------- End of Forwarded Message

17 years, 4 months

I'm tagging the Python 2.2.3 tree

by Barry Warsaw

No more changes please. -Barry

17 years, 4 months

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Python-Dev May 2003