[Python-Dev] python-dev Summary for 2003-03-16 through 2003-03-31
Tue, 1 Apr 2003 20:52:22 -0800 (PST)
You guys have 24 hours to correct my usual bunch of mistakes.
Also give me feedback on the new format for the Quickies section.
python-dev Summary for 2003-03-16 through 2003-03-31
.. _last summary:
PyCon is now over! It was a wonderful experience. Getting to meet people
from python-dev in person was great. The sprint was fun and productive
(work on the AST branch, caching where something is found in an
inheritence tree, and a new CALL_ATTR opcode were all worked on).
Definitely was worth it.
I am trying a new way of formatting the Quickies_ section. I am trying
non-inline implicit links instead of inlined ones. I am hoping this will
read better in the text version of the summary. If you have an opinion on
whether the new or old version is better let me know. And remember, the
last time I asked for an opinion Michael Chermside was the only person to
respond and thus ended up making an executive decision.
.. _PyCon: http://www.python.org/pycon/
`Re: lists v. tuples`__
- `Re: Re: lists v. tuples
This developed from a thread from covered in the `last summary`_ that
discussed the different uses of lists and tuples. By the start date for
this summary, though, it had turned into a discussion on comparisons.
This occured when sorting heterogeneous objects came up. Guido commented
that having anything beyond equality and non-equality tests for
non-related objects does not make sense. This also led Guido to comment
that "TOOWTDI makes me want to get rid of __cmp__" (TOOWTDI is "There is
Only One Way to Do It").
Now before people start screaming bloody murder over the possible future
loss of __cmp__() (which probably won't happen until Python 3), realize
that all comparisons can be done using the six other rich comparisons
(__lt__(), __eq__(), etc.). There is some possible code elegance lost if
you have to use two rich comparisons instead a single __cmp__()
comparison, but it is nothing that will prevent you from doing something
that you couldn't do before.
This all led Guido to suggest introducing the function before(). This
would be used for arbitrary ordering of objects. Alex Martelli said it
would "be very nice if before(x,y) were the same as x<y whenever the
latter doesn't raise an exception, if feasible". He also said that it
should probably "define a total ordering, i.e. the implied equivalence
`Fast access to __builtins__`__
There has been rumblings on the list as of late of disallowing shadowing
of built-ins. Specifically, the idea of someone injecting something into
a module's namespace that overrides a global (by doing something like
``socket.len = lambda x: 42`` from the socket module) is slightly nasty,
rarely done, and prevents the core from optimizing for built-ins.
Raymond Hettinger, in an effort to see how to speed up built-in access,
came up with the idea of replacing opcode calls of LOAD_GLOBAL and replace
them with LOAD_CONST after putting the built-in being called into the
constants table. This would leave shadowing of built-ins locally
unaffected but prevent shadowing at the module. Raymond suggested turning
on this behavior for when running Python -O.
The idea of turning this on when running with the -O option was shot down.
The main argument is that semantics are changed and thus is not acceptable
for the -O flag. It was mentioned that -OO can change semantics, but even
that is questionable.
So this led to some suggestions of how to turn this kind of feature on.
Someone suggested something like a pragma (think Perl) or some other
mechanism at the module level. Guido didn't like this idea since he does
not want modules to be riddled with code to turn on module-level
But all of this was partially shot down when Guido stepped in and
reiterated he just wanted to prevent outside code from shadowing built-ins
for a module. The idea is that if it can be proven that a module does not
shadow a built-in it can output an opcode specific for that built-in, e.g.
len() could output opcode for calling PyOject_Size() if the compiler can
prove that len() is not shadowed in the module at any point.
Neil Schemanauer suggested adding a warning for when this kind of
shadowing is done. Guido said fine as long as extension modules are
exempt. Now no matter how well the warning is coded, it would be
*extremely* difficult to catch something like ``import X; d = X__dict__;
d["len"] = lambda x: 42``. How do you deal with this? By Guido saying he
has not issue saying something like this "is always prohibited". He said
you could still do ``setattr(X, "len", lambda x: 42)``, though, and that
might give you a warning.
The thread that will not die (nor does it look like it will in the near
future; Guido asked to postpone discussing it until he gets back from
`Python UK`_ which will continue the discussion into the next summary. I
am ending up an expert at capabilities against my will. =)
In case you have not been following all of this, capabilities as being
discussed here is the idea that security is based on passing around
references to objects. If you have a reference you can use it with no
restrictions. Security comes in by controlling who you give references
to. So I might ask for a reference to file(), but I won't necessarily get
it. I could, instead, be handed a reference to a restrictive version of
file() that only opens files in an OSs temporary file directory. If that
is not clear, read the `last summary`_ on this thread. And now, on to the
One point made about capabilities is that they partially go against the
Pythonic grain. Since you have to pass capabilities specifically and
shouldn't allow them to be inherited, it does not go with the way you tend
to write Python code.
There were also suggestions to add arguments to import statements to give
a more fine-grained control over them. But it was pointed out that
classes fit this bill.
The idea of limiting what modules are accessible by some code by not using
a universally global scope (i.e., not using sys.modules) but by having a
specific scope for each function was suggested. As Greg Ewing put it, "it
would be dynamic scoping of the import namespace".
While trying to clarify things (which were at PyCon thanks to the Open
Space discussion held there on this subject), a good distinction between a
rexec_ world (as in the module) and a capabilities was made by Guido. In
capabilities, security is based on passing around references that have the
amount of power you are willing for it to have. In a rexec world, it is
based on what powers the built-ins give you; there is no worry about
passing around code. Also, in the rexec world, you can have the idea of a
"workspace" where __builtin__ has very specific definitions of built-ins
that are used when executing untrusted code.
Ka-Ping Yee wrote up an example of some code of what it would be like to
code with capabilities (can be found at XXX ).
.. _Python UK: http://www.python-uk.org/
.. _rexec: http://www.python.org/dev/doc/devel/lib/module-rexec.html
time.tzset() is going to be kept in Python, but only on UNIX. The
testing suite was also loosened so as to not throw as many
stdin and stdout on Windows are TTYs. You can get 3rd-party modules
to get more control over the TTY.
`Who approved PyObject_GenericGetIter()???`__
Splinter threads: `Re: [Python-checkins] python/dist/src/Modules
Raymond Hettinger wrote a function called PyObject_GenericGetIter()
that returned self for objects that were an iterator themselves. Thomas
Wouters didn't like the name and neither did Guido since it was generic at
all; it worked specifically with objects that were iterators themselves.
Thus the function was renamed to PyObject_SelfIter().
A test for posix.getlogin() was failing for Barry Warsaw under XEmacs
(that is what he gets for not using Vim_ =). Thomas Wouters pointed out
it only works when there is a utmp file somewhere. Basically it was
agreed the test that was failing should be removed.
.. _Vim: http://www.vim.org/
Raymond Hettinger reported that a change in `_tkinter.c`_ for a
function led to it returning strings or ints which broke PMW_ (although
having a function return two different things was disputed in the thread;
I think it used to return a string and now returns an int). The
suggestion of making string.atoi() more lenient on its accepted arguments
was made but shot down since it changes semantics. If you want to keep
old way of having everything in Tkinter return strings instead of more
proper object types (such as ints where appropriate), you can put teh line
``Tkinter.wantobjects = 0`` before the first creation of a tkapp object.
.. _PMW: http://pmw.sourceforge.net/
`csv package ready for prime-time?`__
Related: `csv package stitched into CVS hierarchy`__
Skip Montanaro: Okay to move csv_ package from the sandbox into the
Guido van Rossum: Yes.
.. _csv: http://www.python.org/dev/doc/devel/lib/module-csv.html
`string.strip doc vs code mismatch`__
Neal Norwitz asked for someone to look at http://python.org/sf/697220
which updates string.strip() from the string_ module to take an optional
second argument. The patch is still open.
.. _string: http://www.python.org/dev/doc/devel/lib/module-string.html
`Re: More int/long integration issues`__
The point was made that it would be nice if the statement ``if num in
range(...): ...`` could be optimized by the compiler if range() was only
the built-in by substituting it with something like xrange() and thus skip
creating a huge list. This would allow the removal of xrange() without
issue. Guido suggested a restartable iterator (generator would work
wonderfully if you could just get everything else to make what range()
returns look like the list it should be).
`socket timeouts fail w/ makefile()`__
Skip Montanaro discovered that using the makefile() method on a socket
cause the file-like object to not observe the new timeout facility
introduced in Python 2.3. He has since patched it so that it works
properly and that sockets always have a makefile() (wasn't always the case
`New Module? Tiger Hashsum`__
Tino Lange implemented a wrapper for the `Tiger hash sum`_ for Python
and asked how he could get it added to the stdlib. He was told that he
would need community backing before his module could be added in order to
make sure that there is enough demand to warrant the edition.
.. _Tiger hash sum: http://www.cs.technion.ac.il/~biham/Reports/Tiger/
`Icon for Python RSS Feed?`__
Tino Lange asked if an XML RSS feed icon could be added at
http://www.python.org/ for http://www.python.org/channews.rdf . It has
`How to suppress instance __dict__?`__
David Abrahams asked if there was an easy way to suppress an instance
__dict__'s creation from a metaclass. The answer turned out to be no.
`Weekly Python Bug/Patch Summary`__
Another summary can be found at
Skip Montanaro's weekly reminder how Python ain't perfect.
Samuele Pedroni is off relaxing is is going to be offline for two
weeks starting March 23.
Christian Tismer discovered a memory leak in a funky def statement he
came up with. The leak has since been squashed (done at PyCon_ during the
`Checkins to Attic?`__
CVS_ uses something called the Attic to put files that are only in a
branch but not the HEAD of a tree.
.. _CVS: http://www.cvshome.org/
`ossaudiodev tweak needs testing`__
Greg Ward asked people who are running Linux or FreeBSD to execute
``Lib/test/regrtest.py -uaudio test_ossaudiodev`` so as to test his latest
change to ossaudiodev_.
`cvs.python.sourceforge.net fouled up`__
Apparently when you get that nice message from SourceForge_ telling
you that recv() has aborted because of server overloading you can rest
assured that people with checkin rights get to continue to connect since
they get priority.
.. _SourceForge: http://www.sf.net/
`Doc strings for typeslots?`__
You can't add custom docstrings to things stored in typeobject slots
at the C level.
`Compiler treats None both as a constant and variable`__
As of now the compiler outputs opcode that treats None as both a
global and a constant. That will change as some point when assigning to
None becomes an error instead of a warning as it is in Python 2.3;
possibly 2.4 the change will be made.
M.A. Lemburg stated that he questioned whether the iconv codec was
ready for prime-time. There have been multiple issues with it and most
seem to stem from a platform's codec and not ones that come with Python.
This affects all u"".encode() calls when the codec does not come with
Python. Hye-Shik Chang said he would get his iconv codec NG patch up on
SF in the next few days and that would be applied.