[Python-Dev] Python Language Summit EuroPython 2010

[Tim Golden]

Before the main events of EuroPython 2010 a Python Language Summit took
place at the Conference venue in Birmingham. Present were (in the order
they sat around the table):

* Brett Cannon
* Guido van Rossum
* Holger Krekel
* Amaury Forgeot D'Arc
* Georg Brandl
* Péter Szabó
* Ezio Melotti
* Michael Foord
* Mark Dickinson
* Martin von Loewis
* Ronald Oussoren
* Tim Golden
* Marc Andre Lemburg
* Richard Jones

Michael initiated a round-up of current and prospective Python versions for
various implementations. CPython and IronPython have both just released
v2.7 with IronPython offering some Py3 compatibility via a command-line
switch. The recent/current migration of Numpy and SciPy to Py3 should
give a boost to uptake. Amaury confirmed that PyPy currently supports
2.5.2 but is looking to target 2.7.

The PyPy guys also announced a C API bridging layer which should enable
a range of Python extension modules to work directly with PyPy. This is
only a stepping stone by way of broadening support. Brett suggested that
the Unladen Swallow merge to trunk was waiting for some work to complete
on the JIT compiler and Georg, as release manager for 3.2, confirmed that
Unladen Swallow would not be merged before 3.3.

The email module needs some work in Py3. David Murray has been given some
money by the PSF but needs more from other sources to complete the work.
This is hampered by the legalities around commercial organisations making
donations to not-for-profits when those donations are earmarked. Various
suggestions were put forward with no-one sure of the legal issues. Guido
suggested that we should move forward rather than stall for want of legal
advice.

A broad discussion arose concerning the issues debated on web-sig concerning
the WSGI protocol and the bytes vs string issues. Marc Andre brought up the
cgi module which has similar issues under Py3 and other examples were given,
including ftplib, urllib and some os functions. Various solutions were put
forward including a hybrid bytes-with-encoding object. This proposal was widely
unpopular, but two proposals met with broad approval: that certain stdlib
functions might be polymorphic, returning the type of their input as output;
and that the encoding string should include its error-handling. An example
of the first would be that os.getenv ("HOME") would return "/home/tjg" while
os.getenv (b"HOME") would return b"/home/tjg". An example of the latter would
be "utf8:strict". Something of the sort already works for PYTHONIOENCODING.

The issue of a __format__ equivalent for bytes was also raised as was the
idea of object methods to render an object as string or bytes, which could
be used in the polymorphic functions above.

Martin spoke about the state of the stable ABI PEP, indicating that he was
targetting 3.2. This work would reduce the need to recompile extension
modules separately on Windows for every version of Python -- something
especially pertinent when code has been orphaned but is still useful.
The versioned .so files PEP being worked out by Barry Warsaw overlaps with
this PEP and would only be useful for extensions which don't target the
stable ABI.

A messy discussion turned on the question of garbage collection of module
objects, and the order in which finalisers are called if at all, especially
when reference cycles exist. Marc Andre was proposing a __cleanup__ magic function
for Python modules, which would enable the implementer to define the order
in which resources are released / closed down. This is quite a subtle area
and raised the issue of unfinalised objects in a reference cycle whose
memory has been freed out from under them but which still exist. Martin described
the Java approach where finalisers are called once and then flagged so
they are not called again even if their object is resurrected. This sounded
like a useful approach for Python but would break code which expected to
be able to resurrect an object during its __del__ method... which is not
expected to account for much code.

Guido pointed out that no-one can be expected to hold enough of the complexities
of this area of Python's implementation in their head, and that an implementation
of some sort would need to be written so that the corner-cases could emerge.

Ronald described the issues around the version and architecture differences
on Mac OS X and especially around Tkinter (and therefore IDLE). It was agreed that
two installers could be provided: one targetting OS 10.3 on 32-bit Intel/PPC;
the other targetting 10.6 on 32 and 64-bit Intel. This latter would then be
able to use the system's Tk 8.5. The 10.6 binary would also work for 10.5,
which would be indicated in the install docs.

The Mercurial migration should move forward once Dirkjan has finished work
on his thesis. Martin insisted that a for-real repository would have to be
set up so that people can really see how it would work. An outstanding issue
in hg-svn prevents the Python history from being imported, but it should be
fixable. Martin & Tim brought up the issue of externals which the buildbots
use on Windows to bring in and build slightly patched versions of external
libraries such as OpenSSL and sqlite3.

Brett confirmed that he would like to see the stdlib broken out into its
own repository which could then be shared between the different Python
implementations.

A discussion on the Cheeseshop / Package Index highlighted the fact that
the packaging infrastructure has become increasingly important especially
since setuptools, buildout and pip all download from it. Richard produced
graphs showing the increase in package downloads over time, and attributed
the recent slight tail-off to the fact that the toolchains are now becoming
more canny with respect to cacheing and mirroring.

Martin & Richard confirmed that mirrors are now in place and Marc Andre confirmed
that he would be putting together a proposal to have PyPI hosted in the
cloud. Guido pointed out that if an AppEngine implementation were desirable,
he was sure that AppEngine team would support it with resources as needed.
Martin didn't feel that there was a problem with loading on the box in
question; it's the uptime that's behind people's concern as it's now so
essential to installing and deploying Python applications.

Several people outlined the recent heated discussion over the addition
of a checkbox to the PyPI user-registration pages. Tarek has already
undertaken to patch PyPI to move the checkbox back one step, allowing
existing distutils users to register from the command line. At the same
time, Brett advised removing that functionality from distutils2 as
signing up on a web page is no great hardship.