Mailman 3 June 2000 - Python-Dev

Text about cycle GC
by A.M. Kuchling June 29, 2000

June 29, 2000

I've written some text for the What's New article on the GCing of cycles, but it wasn't a topic I paid close attention to at the time, so I'd like corrections. Here's what I've got; please send me comments privately. 6. Optional Collection of Cycles The C implementation of Python uses reference counting to implement garbage collection. Every Python object maintains a count of the number of references pointing to itself, and adjusts the count as references … [View More]are created or destroyed. Once the reference count reaches zero, the object is no longer accessible, since you need to have a reference to an object to access it, and if the count is zero, no references exist any longer. Reference counting has some pleasant properties: it's easy to understand and implement, and the resulting implementation is portable, fairly fast, and reacts well with other libraries that implement their own memory handling schemes. The major problem with reference counting is that it sometimes doesn't realise that objects are no longer accessible, resulting in a memory leak. This happens when there are cycles of references. Consider the simplest possible cycle, a class instance which has a reference to itself: instance = SomeClass() instance.myself = instance After the above two lines of code have been executed, the reference count of instance is 2; one reference is from the variable named "'instance'", and the other is from the "myself"attribute of the instance. If the next line of code is del instance, what happens? The reference count of instance is decreased by 1, so it has a reference count of 1; the reference in the "myself" attribute still exists. Yet the instance is no longer accessible through Python code, and it could be deleted. Several objects can participate in a cycle if they have references to each other, causing all of the objects to be leaked. An experimental step has been made toward fixing this problem. When compiling Python, the -with-cycle-gc (XXX correct option flag?) option can be specified. This causes a cycle detection algorithm to be periodically executed, which looks for inaccessible cycles and deletes the objects involved. Why isn't this enabled by default? Running the cycle detection algorithm takes some time, and some tuning will be required to minimize the overhead cost. It's not yet obvious how much performance is lost, because benchmarking this is tricky and depends sensitively on how often the program creates and destroys objects. XXX is this actually the correct reason? Or is it fear of breaking software that runs happily while leaving garbage? Several people worked on this problem. Early versions were written by XXX1, XXX2. (I vaguely remember several people writing first cuts at this. Anyone recall who?) The implementation that's in Python 1.6 is a rewritten version, this time done by Neil Schemenauer. Lots of other people offered suggestions along the way, such as (in alphabetical order) Marc-André Lemburg, Tim Peters, Greg Stein, Eric Tiedemann. (XXX other names? If you feel you should be added, e-mail me). The March 2000 archives of the python-dev mailing list contain most of the relevant discussion, especially in the threads titled ``Reference cycle collection for Python'' and ``Finalization again''. [View Less]

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how do I build pyexpat?
by Jeremy Hylton June 29, 2000

June 29, 2000

Setup.in contains the following comment: # (Note: the expat build process doesn't yet build a libexpat.a; you can # do this manually while we try convince the author to add it.) I've got expat, and I've built it, but I don't have any idea how to build libexpat.a. It may be possible to do it manually, but it would help a lot if the comments could say how to build it or contain a link to instructions on how to build it. Jeremy

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re: ucnhash
by Bill Tutt June 29, 2000

June 29, 2000

Re: ucnhash and where the stuff gets tested Doesn't matter to me where the test goes. WRT how big it is, thats why its dynamically loaded at run time. If you don't compile it at all, then the \N{...} syntax just won't owrk. Re: static vs. staticforward I can actually do a patch for that, and regen ucnhash.c for you. Re: "" vs. <> Whats wrong with what I'm currently doing? All of the .h files I'm including are on the include file path. "" usage just means stick "." before everything … [View More]

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add Demo/imputil/importers.py ?
by Greg Stein June 29, 2000

June 29, 2000

A while back, I pulled the "demo" importers out of imputil.py. I think those should be added into Demo/imputil/. It would also be Goodness to include JimA's zipimporter. Where would that go? Cheers, -g -- Greg Stein, http://www.lyra.org/

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ucnhash module
by Jack Jansen June 29, 2000

June 29, 2000

I'm a bit worried about the ucnhash module and its huge size. I didn't follow the discussion closely at the time, because I thought I could always exclude it from the Pythons without dynamic linking, but now it seems that if i don't include it test_unicode doesn't run anymore. Is this a problem with test_unicode, or should I consider ucnhash a mandatory module? (BTW: there were also a couple of bugs in the module, include <> in stead of include "", and static in stead of staticforward … [View More]

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Re: [Python-checkins] CVS: python/dist/src/Modules _sre.c,2.4,2.5
by Greg Stein June 29, 2000

June 29, 2000

Euh... can we get a bit more information in that checkin message. "towards 1.6b1" says zippo about what is changing or why. Cheers, -g On Thu, Jun 29, 2000 at 01:57:57AM -0700, Fredrik Lundh wrote: > Update of /cvsroot/python/python/dist/src/Modules > In directory slayer.i.sourceforge.net:/tmp/cvs-serv11206 > > Modified Files: > _sre.c > Log Message: > towards 1.6b1 > > Index: _sre.c > =================================================================== > … [View More]

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Another Python-based company makes good...
by Skip Montanaro June 29, 2000

June 29, 2000

Saw this on InfoBeat today: ** Yahoo to buy EGroups Yahoo said it would buy e-mail service provider EGroups (www.egroups.com) for $437.5 million in stock to enhance the Internet giant's communications services. Yahoo (YHOO) said it would issue 3.43 million shares of stock for all of EGroups shares, options, and warrants. The purchase will be accounted for as a pooling of interests and is expected to close in the third quarter. Yahoo said it would report a one-… [View More]

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RTFM: SourceForge access for Win32
by Greg Stein June 28, 2000

June 28, 2000

All right guys... all this banter about setting up CVS access for Win32 users has been quite silly. Did anybody even stop to look at the docs? http://sfdocs.sourceforge.net/sfdocs/ In particular: http://sfdocs.sourceforge.net/sfdocs/display_topic.php?topicid=19 http://sfdocs.sourceforge.net/sfdocs/display_topic.php?topicid=20 http://sfdocs.sourceforge.net/sfdocs/display_topic.php?topicid=46 There is also a new tool available (released today); http://sfsetup.sourceforge.net/ Cheers, -g … [View More]

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httplib doc (was: CVS: python/dist/src/Doc/lib libhttplib.tex,1.19,1.20)
by Greg Stein June 28, 2000

June 28, 2000

Please mark me for a TODO to update the httplib doc. For example, the code below is more effectively written as: h = httplib.HTTPConnection('www.musi-cal.com') h.request('POST', '/cgi-bin/query', paramstring, {'Accept': 'text/plain'}) response = h.getresponse() print response.status # should be 200 data = response.read() # get the raw HTML Note that 'Accept' is usually not a required header and can be omitted in most scenarios. I left it in the example simply to show how to fully map … [View More]between the old/new APIs. [ Content-Length and Host are sent automatically by HTTPConnection. ] Cheers, -g On Wed, Jun 28, 2000 at 02:51:46PM -0700, Fred L. Drake wrote: > Update of /cvsroot/python/python/dist/src/Doc/lib > In directory slayer.i.sourceforge.net:/tmp/cvs-serv5474/lib > > Modified Files: > libhttplib.tex > Log Message: > > Skip Montanaro <skip(a)mojam.com>: > Added an example of using an HTTP POST request. > > > Index: libhttplib.tex > =================================================================== > RCS file: /cvsroot/python/python/dist/src/Doc/lib/libhttplib.tex,v > retrieving revision 1.19 > retrieving revision 1.20 > diff -C2 -r1.19 -r1.20 > *** libhttplib.tex 1999/04/22 16:47:27 1.19 > --- libhttplib.tex 2000/06/28 21:51:43 1.20 > *************** > *** 115,119 **** > \nodename{HTTP Example} > > ! Here is an example session: > > \begin{verbatim} > --- 115,119 ---- > \nodename{HTTP Example} > > ! Here is an example session that uses the \samp{GET} method: > > \begin{verbatim} > *************** > *** 129,131 **** > --- 129,148 ---- > >>> data = f.read() # Get the raw HTML > >>> f.close() > + \end{verbatim} > + > + Here is an example session that shows how to \samp{POST} requests: > + > + \begin{verbatim} > + >>> import httplib, urllib > + >>> params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0}) > + >>> h = httplib.HTTP("www.musi-cal.com:80") > + >>> h.putrequest("POST", "/cgi-bin/query") > + >>> h.putheader("Content-length", "%d" % len(params)) > + >>> h.putheader('Accept', 'text/plain') > + >>> h.putheader('Host', 'www.musi-cal.com') > + >>> h.endheaders() > + >>> h.send(paramstring) > + >>> reply, msg, hdrs = h.getreply() > + >>> print errcode # should be 200 > + >>> data = h.getfile().read() # get the raw HTML > \end{verbatim} > > > _______________________________________________ > Python-checkins mailing list > Python-checkins(a)python.org > http://www.python.org/mailman/listinfo/python-checkins -- Greg Stein, http://www.lyra.org/ [View Less]

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exceptions trouble
by Fredrik Lundh June 28, 2000

June 28, 2000

import traceback try: raise SyntaxError, "argument" except: traceback.print_exc() prints: Traceback (most recent call last): File "test.py", line 3, in ? raise SyntaxError, "argument" Traceback (most recent call last): File "test.py", line 5, in ? traceback.print_exc() File "C:\py16\lib\traceback.py", line 182, in print_exc print_exception(etype, value, tb, limit, file) File "C:\py16\lib\traceback.py", line 110, in print_exception lines = format_exception_only(… [View More]

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