python-dev summary, Dec. 1-15

Sun, 7 Jan 2001 22:37:51 -0500

Python-dev summary, December 1-15, 2000
=======================================

To comment on material in this python-dev summary, you can simply post
to comp.lang.python / <python-list@python.org>.  These summaries are
archived at <URL:http://www.amk.ca/python/dev/>.

A busy two weeks, particularly for the PEPs, where there were several
major edits and changes of status.  The deadline for PEPs for Python
2.1 is Dec. 15; after this point, no new PEPs will be added to the
list (though they may be taken off the list if implementation turns
out to be impractical or the proposed idea proves a bad one).

I expect the next two week period to be slow on python-dev, since most
people will be off on vacation, celebrating the holiday, or otherwise
distracted.

Unit testing
============

Jeremy Hylton wondered about adding a unit testing framework to
Python.  The list of suggested candidates produced by people on
python-dev is:

PyUnit:
        http://pyunit.sourceforge.net
unittest.py from Quixote:
        http://x63.deja.com/=usenet/getdoc.xp?AN=683946404 (intro)
        http://www.amk.ca/python/unittest.html (docs)
doctest:
        http://starbase.neosoft.com/~claird/comp.lang.python/doctest.html
David Goodger pointed out another unit testing implementation:
        http://www.objectmentor.com/freeware/downloads.html

If readers of this summary know of other unit testing tools for
Python, please let python-dev know about them.

Peter Funk compared doctest and Quixote's unittest.py: "After reading
Andrew's docs, I think Quixote basically offers three additional
features if compared with Tim Peters 'doctest'."
        http://mail.python.org/pipermail/python-dev/2000-December/010882.html

__findattr__
============

Barry Warsaw submitted PEP 231, suggesting a new __findattr__() hook.
"My hope is that __findattr__() would eliminate most, if not all, the
need for ExtensionClass, at least within the Zope and ZODB contexts.
I haven't tried to implement Persistent using it though."
        http://python.sourceforge.net/peps/pep-0231.html

__findattr__ would be called on every attribute access, unlike
__getattr__ which is only called when the attribute is not found in an
instance's dictionary.  __findattr__ poses a self-referential problem,
though; how would the __findattr__ access any of the contents of an
instance, since it would be recursively called on any attribute access
within the body of the __findattr__()?  Barry's PEP used a .infindattr
attribute that would be set to true inside a __findattr__ method, but
that isn't thread-safe.  Other approaches were suggested -- store this
in the thread state, compile special tricks into the bytecode compiled
for __findattr__ calls -- but nothing seemed very clean.

GvR's response to all this was "I'm unconvinced by the __findattr__
proposal as it now stands," and went on to reject the PEP.  

Iterating through dictionaries
==============================

Discussion about iterating through dictionaries without constructing a
list of keys (the .popitem() proposed in the 2 weeks covered by the
previous python-dev summary).  Christian Tismer analyzed the math for
the hash tables that underly dictionaries: "The powers of ľ reach all
these patterns. Therefore, each pattern *is* some power of ľ. By
multiplication with ľ we can reach every possible pattern exactly
once.  Since these patterns are used as distances from the primary
hash-computed slot modulo 2^n, and the distances are never zero, all
slots can be reached."  
        http://mail.python.org/pipermail/python-dev/2000-December/010913.html

Christian went on to use this to attempt to improve the hashing
algorithm used for dictionaries: "While the current algorithm is 110
times slower on a worst case dict (quadratic behavior), the new
algorithm accounts a little for the extra cycle, but is only 4 times
slower."
        http://mail.python.org/pipermail/python-dev/2000-December/011085.html

Tim thought that the GF() hashing wasn't relevant to the problem of
consuming the entire contents of a dictionary, and proposed a
different popitem() implementation:
        http://mail.python.org/pipermail/python-dev/2000-December/010916.html

PEP Progress
============

PEP 207, the Rich Comparison PEP, was updated by Guido.  Rich
comparisons would provide more flexibility, making it possible to
separately overload <, >, <=, >=, ==, != in classes, and to return
something besides a Boolean result.  The idea has been around for
years, and David Ascher wrote an earlier proposal a few years ago.
PEP 207 is mostly a re-editing of David's proposal by GvR.
        http://python.sourceforge.net/peps/pep-0207.html

Neil Schemenauer has been beavering away at PEP 208, clarifying the
semantics and the implementation of __coerce__:
        http://python.sourceforge.net/peps/pep-0208.html
The patch for Neil's reference implementation is patch #102652:
        http://sourceforge.net/patch/?func=detailpatch&patch_id=102652&group_id=5470

GvR approved PEP 217, written by Moshe Zadka: "Display Hook for
Interactive Use".  This PEP adds a sys.displayhook(obj) function which
is called to display results in the interactive interpreter, making it
easy to use str() or a fancy pretty-printing function instead of just
the default repr().
        http://python.sourceforge.net/peps/pep-0217.html

Jeremy Hylton updated PEP 227, "Statically Nested Scopes":
        http://python.sourceforge.net/peps/pep-0227.html
Jeremy's prototype implementation is available as patch #102864:
        http://sourceforge.net/patch/?func=detailpatch&patch_id=102864&group_id=5470

PEP 230, a warning framework proposal, also received GvR's final
approval during this time period.
        http://python.sourceforge.net/peps/pep-0230.html

Three new PEPS: #231 was born and died during this time period, and is
discussed in the __findattr__ section above.  #232 is Barry Warsaw's
proposal for function attributes, and 233 is Paul Prescod's proposal
for an on-line help facility in the interpreter.
        http://python.sourceforge.net/peps/pep-0232.html
        http://python.sourceforge.net/peps/pep-0233.html

Deprecating the string module?
==============================

GvR made a few checkins that replaced uses of string.* functions with
string methods.  Neil Schemenauer asked "Can you explain the logic
behind this recent interest in removing string functions from the
standard library?  It it performance?  Some unicode issue?"

Guido's response was "As a realistic test of the warnings module I
played with some warnings about the string module, and then found that
most of the std library modules use it, triggering an
extraordinary amount of warnings."
        http://mail.python.org/pipermail/python-dev/2000-December/011051.html

Tim wondered if this was really necessary: "'string' is right up there
with 'os' and 'sys' as a FIM (Frequently Imported Module), so the
required code changes will be massive.  As a user, I don't see what's
in it for me to endure that pain: the string module functions work
fine!"
        http://mail.python.org/pipermail/python-dev/2000-December/011054.html

This sparked a lengthy debate; *is* the string module going away?
Guido dislikes the duplication in having both a string module and
string methods, though it would only disappear several major releases
in the future; Barry Warsaw prefers string methods over string
functions.  While Greg Wilson also liked removing the duplication of
functionality, GvR and Barry seem to be otherwise alone on this point;
no one sees the need to remove the string module, and some people
don't like string methods that much, particularly in certain cases
such as the .join() method.

Other stuff
===========

Thomas Gellekum submitted a wrapper for the panel library that comes
with ncurses.  However, the additional code would make _cursesmodule.c
even larger (60K, 2500 lines), so instead AMK proposed splitting up
the C module.  Fred Drake pointed out a better way, using CObjects to
export an API:
        http://mail.python.org/pipermail/python-dev/2000-December/010971.html

A patch was submitted to SourceForge, and is currently waiting for
more people to look at it: 
        http://sourceforge.net/patch/?func=detailpatch&patch_id=102813&group_id=5470

Related Links
=============

Python-dev archives:
        http://www.python.org/pipermail/python-dev/

Python project page on SourceForge:
        http://sourceforge.net/projects/python

Python Enhancement Proposals (PEPs):
        http://python.sourceforge.net/peps/