🌐 Mailman 3 December 2009 - Python-list - python.org

AIX installation can't find zlib
by Larry Whitley Nov. 3, 2011

Nov. 3, 2011

I've just installed the 1.5.2 source distribution on an AIX system and when I say "import zlib" it responds: >>> import zlib Traceback (innermost last): File "<stdin>", line 1, in ? ImportError: No module named zlib >>> I'm not sure where zlib is supposed to be. It's not in the Lib subdirectory of Python-1.5.2. In the Modules subdirectory I find zlibmodule.c. Nothing germaine in the Objects subdirectory. Looked at config.log and config.status, no mention of zlib. Looking at the sys.path I see: .../ldw/Python-1.5.2> python Python 1.5.2 (#1, Jul 26 2000, 14:21:56) [C] on aix4 Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam >>> import sys >>> sys.path ['', '/.../rchland.ibm.com/fs/u1/ldw/Projects/Programs/wtCache', '/.../rchland.ibm.com/fs/u1/ldw/Python-1.5.2/Lib/', '/.../rchland.ibm.com/fs/u1/ldw/Python-1.5.2/Lib/plat-aix4', '/.../rchland.ibm.com/fs/u1/ldw/Python-1.5.2/Lib/lib-tk', '/.../rchland.ibm.com/fs/u1/ldw/Python-1.5.2/Modules'] >>> Any suggestions? Larry

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PEP 372 -- Adding an ordered directory to collections
by Armin Ronacher Aug. 7, 2011

Aug. 7, 2011

Abstract ======== This PEP proposes an ordered dictionary as a new data structure for the ``collections`` module, called "odict" in this PEP for short. The proposed API incorporates the experiences gained from working with similar implementations that exist in various real-world applications and other programming languages. Rationale ========= In current Python versions, the widely used built-in dict type does not specify an order for the key/value pairs stored. This makes it hard to use dictionaries as data storage for some specific use cases. Some dynamic programming languages like PHP and Ruby 1.9 guarantee a certain order on iteration. In those languages, and existing Python ordered-dict implementations, the ordering of items is defined by the time of insertion of the key. New keys are appended at the end, keys that are overwritten and not moved. The following example shows the behavior for simple assignments: >>> d = odict() >>> d['parrot'] = 'dead' >>> d['penguin'] = 'exploded' >>> d.items() [('parrot', 'dead'), ('penguin', 'exploded')] That the ordering is preserved makes an odict useful for a couple of situations: - XML/HTML processing libraries currently drop the ordering of attributes, use a list instead of a dict which makes filtering cumbersome, or implement their own ordered dictionary. This affects ElementTree, html5lib, Genshi and many more libraries. - There are many ordererd dict implementations in various libraries and applications, most of them subtly incompatible with each other. Furthermore, subclassing dict is a non-trivial task and many implementations don't override all the methods properly which can lead to unexpected results. Additionally, many ordered dicts are implemented in an inefficient way, making many operations more complex then they have to be. - PEP 3115 allows metaclasses to change the mapping object used for the class body. An ordered dict could be used to create ordered member declarations similar to C structs. This could be useful, for example, for future ``ctypes`` releases as well as ORMs that define database tables as classes, like the one the Django framework ships. Django currently uses an ugly hack to restore the ordering of members in database models. - Code ported from other programming languages such as PHP often depends on a ordered dict. Having an implementation of an ordering-preserving dictionary in the standard library could ease the transition and improve the compatibility of different libraries. Ordered Dict API ================ The ordered dict API would be mostly compatible with dict and existing ordered dicts. (Note: this PEP refers to the Python 2.x dictionary API; the transfer to the 3.x API is trivial.) The constructor and ``update()`` both accept iterables of tuples as well as mappings like a dict does. The ordering however is preserved for the first case: >>> d = odict([('a', 'b'), ('c', 'd')]) >>> d.update({'foo': 'bar'}) >>> d collections.odict([('a', 'b'), ('c', 'd'), ('foo', 'bar')]) If ordered dicts are updated from regular dicts, the ordering of new keys is of course undefined again unless ``sort()`` is called. All iteration methods as well as ``keys()``, ``values()`` and ``items()`` return the values ordered by the the time the key-value pair was inserted: >>> d['spam'] = 'eggs' >>> d.keys() ['a', 'c', 'foo', 'spam'] >>> d.values() ['b', 'd', 'bar', 'eggs'] >>> d.items() [('a', 'b'), ('c', 'd'), ('foo', 'bar'), ('spam', 'eggs')] New methods not available on dict: ``odict.byindex(index)`` Index-based lookup is supported by ``byindex()`` which returns the key/value pair for an index, that is, the "position" of a key in the ordered dict. 0 is the first key/value pair, -1 the last. >>> d.byindex(2) ('foo', 'bar') ``odict.sort(cmp=None, key=None, reverse=False)`` Sorts the odict in place by cmp or key. This works exactly like ``list.sort()``, but the comparison functions are passed a key/value tuple, not only the value. >>> d = odict([(42, 1), (1, 4), (23, 7)]) >>> d.sort() >>> d collections.odict([(1, 4), (23, 7), (42, 1)]) ``odict.reverse()`` Reverses the odict in place. ``odict.__reverse__()`` Supports reverse iteration by key. Questions and Answers ===================== What happens if an existing key is reassigned? The key is not moved but assigned a new value in place. This is consistent with existing implementations and allows subclasses to change the behavior easily:: class movingcollections.odict): def __setitem__(self, key, value): self.pop(key, None) odict.__setitem__(self, key, value) What happens if keys appear multiple times in the list passed to the constructor? The same as for regular dicts: The latter item overrides the former. This has the side-effect that the position of the first key is used because the key is actually overwritten: >>> odict([('a', 1), ('b', 2), ('a', 3)]) collections.odict([('a', 3), ('b', 2)]) This behavior is consistent with existing implementations in Python, the PHP array and the hashmap in Ruby 1.9. Why is there no ``odict.insert()``? There are few situations where you really want to insert a key at an specified index. To avoid API complication, the proposed solution for this situation is creating a list of items, manipulating that and converting it back into an odict: >>> d = odict([('a', 42), ('b', 23), ('c', 19)]) >>> l = d.items() >>> l.insert(1, ('x', 0)) >>> odict(l) collections.odict([('a', 42), ('x', 0), ('b', 23), ('c', 19)]) Example Implementation ====================== A poorly performing example implementation of the odict written in Python is available: `odict.py <http://dev.pocoo.org/hg/sandbox/raw-file/tip/ odict.py>`_ The version for ``collections`` should be implemented in C and use a linked list internally. Other implementations of ordered dicts in various Python projects or standalone libraries, that inspired the API proposed here, are: - `odict in Babel`_ - `OrderedDict in Django`_ - `The odict module`_ - `ordereddict`_ (a C implementation of the odict module) - `StableDict`_ - `Armin Rigo's OrderedDict`_ .. _odict in Babel: http://babel.edgewall.org/browser/trunk/babel/util.py?rev=374#L178 .. _OrderedDict in Django: http://code.djangoproject.com/browser/django/trunk/django/utils/datastructu… .. _The odict module: http://www.voidspace.org.uk/python/odict.html .. _ordereddict: http://www.xs4all.nl/~anthon/Python/ordereddict/ .. _StableDict: http://pypi.python.org/pypi/StableDict/0.2 .. _Armin Rigo's OrderedDict: http://codespeak.net/svn/user/arigo/hack/pyfuse/OrderedDict.py Future Directions ================= With the availability of an ordered dict in the standard library, other libraries may take advantage of that. For example, ElementTree could return odicts in the future that retain the attribute ordering of the source file. Copyright ========= This document has been placed in the public domain.

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Anybody use web2py?
by AppRe Godeck March 3, 2011

March 3, 2011

Just curious if anybody prefers web2py over django, and visa versa. I know it's been discussed on a flame war level a lot. I am looking for a more intellectual reasoning behind using one or the other.

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Python 3.1 cx_Oracle 5.0.2 "ImportError: DLL load failed: The specified module could not be found."
by André Jan. 24, 2011

Jan. 24, 2011

Hello, I'm trying to get Python 3.1 and cx_Oracle 5.02 (cx_Oracle-5.0.2-10g.win32-py3.0.msi) to connect to an Oracle 11.1.0.7.0 database via OraClient10g 10.2.0.3.0 with Pydev 1.5.1.1258496115 in Eclipse 20090920-1017 on Windows XP SP 3 v2002. The import cx_Oracle line appears as an unresolved import and when I run the application I get the following error to console: Traceback (most recent call last): File "FILEPATHHERE", line 1, in <module> import cx_Oracle ImportError: DLL load failed: The specified module could not be found. Apparently the error is caused by cx_Oracle not being able to find the Oracle client DLLs (oci.dll and others). The client home path and the client home path bin directory are in the PATH System Variable and oci.dll is there. I tried getting the Oracle Instant Client (instantclient-basic- win32-11.1.0.7.0.zip from http://www.oracle.com/technology/software/tech/oci/instantclient/htdocs/win…) and installing it as directed. I added the instant client path to the PATH System Variable but that didn't work either. I have scoured the internet and have not found a solution. Please help!

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Re: parse date/time from a log entry with only strftime (and no regexen)
by andrew cooke Nov. 12, 2010

Nov. 12, 2010

> > ValueError: unconverted data remains: this is the remainder of the log > > line > > that I do not care about you could catch the ValueError and split at the ':' in the .args attribute to find the extra data. you could then find the extra data in the original string, use the index to remove it, and re-parse the time. ugly, but should work. andrew

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Re: *Advanced* Python book?
by Michele Simionato March 25, 2010

March 25, 2010

On Jan 16, 9:27 pm, mk <mrk...(a)gmail.com> wrote: > Hello everyone, > > I looked for it I swear, but just can't find it. > > Most Python books seem to focus on examples of how to call functions > from standard library. I don't need that, I have online Python > documentation for that. > > I mean really advanced mental gymnastics, like gory details of how > Python objects operate, how to exploit its dynamic capabilities, dos and > donts with particular Python objects, advanced tricks, everything from > chained decorators to metaprogramming. Dive Into Python comes closest to > this ideal from what I have found, but still not far enough. > > Anybody found such holy grail? > > Regards, > mk "Expert Python Programming" by Tarek Ziadé is quite good and I wrote a review for it: http://www.artima.com/weblogs/viewpost.jsp?thread=240415 There is plenty of info about Advanced Python on the net, much more than in book form. Come to think of it, there are my Oxford lectures (the title was exactly "Advanced Python Programming") and I could republish it on my blog, since I cannot find them on the net anymore. Michele Simionato

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web sound recording with python
by kernus March 16, 2010

March 16, 2010

I need a web-based sound recording application and upload the sound data to a web server (python cgi?). the project is web voice search, so the web cgi would be a voice search server. any idea about the whole solution(web page and the python cgi)? thanks

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Turtle graphics speed(). Seems broken
by Alexander.Oot＠gmail.com Feb. 28, 2010

Feb. 28, 2010

I think the speed function may be broken from the turtle graphics package "from turtle import * speed('fastest') forward(50)" I have tried all of the different speed settings, but I get no change in the turtle's speed.... does anyone know how to fix this?

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Combining C and Python programs
by Sortie Feb. 23, 2010

Feb. 23, 2010

I want to write a program that will use ode for the physics simulation, whose python bindings are outdated. So I'm writing the physics engine in C and want to write the drawing code in Python. What will be the best way of making those two programs work together? THe physics engine won't have to run concurrently with the drawing code. It will only return some position data so they can be drawn.

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Re: Portable way to tell if a process is still alive
by Nobody Jan. 28, 2010

Jan. 28, 2010

On Tue, 29 Dec 2009 12:35:11 +0430, Laszlo Nagy wrote: > Suppose we have a program that writes its process id into a pid file. > Usually the program deletes the pid file when it exists... But in some > cases (for example, killed with kill -9 or TerminateProcess) pid file is > left there. I would like to know if a process (given with its process > id) is still running or not. I know that this can be done with OS > specific calls. But that is not portable. It can also be done by > executing "ps -p 23423" with subprocess module, but that is not portable > either. Is there a portable way to do this? > > If not, would it be a good idea to implement this (I think very > primitive) function in the os module? Not only is there no way to do it portably, there is no way to do it reliably for the general case. The problem is that processes do not have unique identifiers. A PID only uniquely identifies a running process; once the process terminates, its PID becomes available for re-use. On Unix, it's easy enough to detect whether a given PID is in use: kill(pid, 0) will fail with ESRCH if the pid isn't in use. But if the PID *is* in use, you don't know whether it's being used for the process which wrote the PID file, or if that process died and its PID is now being re-used by another process. A more reliable approach would be for the creator to write not only its PID, but also its start time to the file. Any subsequent process which re-uses the PID is bound to have a later start time. However, the difference could conceivably be less than a second, and getting the start time of a process to better than a second isn't portable between Unices, and may not even be possible. More reliable still would be for the creator to place a lock on the PID file, then test for the presence of the lock. Ensure that testing for the lock doesn't itself lock the file in a way which could fool other processes testing for the presence of a lock; e.g. have the creator place an exclusive lock and test by attempting to place a shared lock.

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