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python-dev Summary for 2006-04-16 through 2006-04-30

Contents

[The HTML version of this Summary is available at http://www.python.org/dev/summary/2006-04-16_2006-04-30]

Announcements

Python 2.5 alpha 2 released

Python 2.5 alpha 2 was released on April 27th. If you haven't tried it out yet, now's the time! PEP 356 has more details and the full schedule.

Contributing threads:

QOTF: Quote of the Fortnight

Phillip J. Eby, on the social behavior of package distributors (and why setuptools goes to such efforts to guess what package distributors were really trying to do):

The problem isn't fundamentally a technical one, but a social one. You can effect social change through technology, but not by being some random guy with a nagging 'bot.

(And yes, Phillip, you can nominate yourself for QOTF.) ;-)

Contributing thread:

Summaries

Adding setuptools to the stdlib

Phillip J. Eby started checking in some of the setuptools modules for Python 2.5. People started to get nervous about some of the modules because:

  • Setuptools changes the distutils "install" command to install everything as zipfile eggs
  • Setuptools changes the distutils "sdist" command to automate generation of MANIFEST.in and MANIFEST.
  • Setuptools adds 'site.py' files so that .pth files are processed in PYTHONPATH directories.
  • Setuptools monkey-patches three classes from distutils: Distribution, Command, and Extension.

While most people recognized the need for the features that setuptools provides, a number of them objected to introducing setuptools as a new package and instead argued for merging setuptools into distutils. Phillip said that such a merge might be possible, but that there were a fair number of backwards compatibility concerns (e.g. its redefinition of the "install" and "sdist" commands) and that it would make it much harder for him to maintain external versions of setuptools compatible with Python 2.3 and 2.4.

In the end, Phillip suggested withdrawing setuptools from Python 2.5, and figuring out how to merge setuptools into distutils for the 2.6 release. In particular, he asked for help with the mostly trivial porting of the "alias", "rotate", "saveopts" and "setopt" commands. Additionally, he made available some information about the setuptools internals for anyone who wanted to see better what was going on behind the scenes.

Contributing threads:

PEP 343: The "with" Statement

A.M. Kuchling asked about some terminology in the PEP 343 documentation. Originally, the objects with __enter__ and __exit__ methods which were used in the with-statement were called "context managers". When the additional __context__ method was introduced, the term "manageable context" was given to objects that provided it. At PyCon, the PEP was changed to switch the terms, though the names of decimal.Context and contextlib.contextmanager were not changed correspondingly. This all led to a rather confusing discussion where people argued over the terminology, appropriately summarized in this quote by Phillip J. Eby:

...everybody has been perfectly clear, we just haven't really gotten on the same page about which words mean what.

People then played around with a variety of alternative terms ("context factory", "context specifier", etc.) but in the end, Guido decided that it was much clearer to just drop the __context__ method entirely -- most use-cases at the time just had __context__ returning self, and the few use-cases that didn't could be accomodated with an appropriately named method or function. And dropping the __context__ method meant that only the term "context manager" was necessary, removing most of the earlier terminological confusion.

Contributing threads:

Dropping __init__.py requirement for subpackages

After some pressure from other Googlers, Guido suggested that Python drop the requirement that subpackages have an __init__.py file (though top-level packages would still require one). People were concerned that a number of non-subpackage directories would suddenly become packages, e.g. "test" in the Python distribution. There was also some concern about tools that depended on the current requirement -- any tool that currently searches directories for __init__.py files would have to be updated to work with the new semantics. In the end, Thomas Wouters provided a patch that makes Python now issue a warning when it would have imported a module but failed to because __init__.py was missing.

Contributing threads:

Python and Visual Studio 2005 Express

Guido noticed that Microsoft had announced that Visual Studio 2005 express will be free forever, and asked if Python should try to accomodate this. People seemed to think that switching to Visual Studio 2005 for Python 2.5 was too soon but that 2.6 might be a reasonable candidate, particularly since Microsoft no longer provides downloads for the Visual Studio 2003 compiler.

Contributing thread:

Adding wsgiref to the stdlib

Guido suggested adding Phillip J. Eby's reference implementation of PEP 333 (the Web Server Gateway Interface) to the standard library. People were generally in favor, though there was some brief discussion about adding a few extras including Ian Bicking's paste.lint validator and a simple dispatch mechanism. It looked like wsgiref would be added in time for Python 2.5.

Contributing threads:

Buildbots on Windows

Some of the Windows buildbots were hanging when the buildbot slave terminated the run early, but failed to terminate python_d.exe, thus making it impossible to recompile anything (since python_d.exe cannot be deleted while running on Windows). No one was certain what was causing the problems (though it seemed like it might be some sort of indexing service running in the background) but Martin v. Löwis was able to unstick the machines by creating a kill_python.exe application which looks for python_d.exe and kills it.

Contributing thread:

Externally maintained packages PEP

Following up on work from the last fortnight, Brett Cannon put together information on all the packages like sqlite and elementtree that are part of the Python standard library, but have their central repository somewhere else. It looked like a PEP would soon be forthcoming.

Contributing threads:

PEP 359: The "make" statement

Discussion continued on PEP 359's "make" statement continued, looking in particular at ways that breaking the parallel with the class statement might make the "make" statement easier to use. In the end Guido asked me to kill the discussion, so I withdrew the PEP.

Contributing threads:

PEP 3102: Keyword-only arguments

Talin introduced PEP 3102 which proposes support for "keyword-only" arguments, that is, arguments that must be specified with the name=value keyword syntax, not as positional arguments. The proposal came in two parts:

  • Allowing keyword arguments after varargs, e.g.:

    def add_option(*opts, action='store', type='string', ...)

  • Allowing keyword arguments with no varargs, e.g.:

    def compare(a, b, *, key=None):

There was widespread support for the first part of the PEP, particularly since such signatures exist in functions like the builtin min and max already (which gained key= arguments in Python 2.5). The latter part people were unsure of, and suggested a variety of other syntaxes, though Guido had already decided on the "*" syntax. Discussion continued on this issue into the next fortnight.

Contributing thread:

String formatting for size_t objects

Brett Cannon ran into some problems with the formatting of size_t objects. What was really needed was the C99 "z" printf modifier, but since Python aims for C89 conformance, that can't be used unconditionally. In the end, Brett Cannon modified Python's config to test if the "z" modifier is supported and then used that whenever possible.

Contributing threads:

The Grammar file and SyntaxErrors

In working on a parser for a subset of the Python language, Michael Foord ran into some troubles using the Grammar/Grammar file in the Python distribution. In particular, the problem he was having was the entry:

list_for: 'for' exprlist 'in' testlist_safe [list_iter]

which indicates that any expression list can be used as the assignment expression in a list comprehension, so that code like the following is valid by the Grammar file:

[1 for 1 in n]

Of course Python doesn't allow this, but as Guido explained, the expression that Python really wants is not LL1, so Python fudges it in the parser, and then issues a SyntaxError later by checking that the nodes in the parse tree actually match the restricted type of nodes required.

Contributing thread:

Pybench now in Python SVN

Marc-Andre Lemburg offered to contribute pybench to Python in response to a previous thread indicating some of the problems with pystone. It's now checked in under the Tools directory.

Contributing thread:

Adding threading.released()

Nick Coghlan asked if the released() function suggested in PEP 343 should be added for Python 2.5 to support code like:

def thread_safe():
    with sync_lock:
        # This is thread-safe
        with released(sync_lock):
            # Perform long-running or blocking operation
            # that doesn't need to hold the lock
        # We have the lock back here

While it seemed occasionally useful (e.g. in the implementation of threading._Condition), this one looked like it would be put off until folks had had more experience with context managers.

Contributing thread:

Removing the me_hash for dicts

Kirat Singh asked about removing me_hash from the dict struct to save some space. People generally seemed opposed to trading off speed for space, particularly since it would slow down classes that define their own __hash__.

Contributing thread:

PEP 3101: Advanced String Formatting

Talin introduced PEP 3101 which proposes a new formatting system through a new string.format() method. This would allow specifying items through both positional and keyword arguments, as well as allowing user-defined classes to support their own set of format specifiers, e.g.:

"The story of {0}, {1}, and {c}".format(a, b, c=d)
"Today is: {0:%x}".format(datetime.now())

There was some brief discussion about how to escape the brace characters, and some opposition to the compound name syntax (which allowed __getitem__-style access using a dotted notation) before the thread trailed off.

Contributing thread:

Replacing SourceForge

Brett Cannon asked for some things that people liked and disliked about SourceForge as the Infrastructure committee moved forward on finding a replacement tracker for SF. There weren't too many positive comments, but some of the things SF was missing are:

  • A way to flag a patch as "reviewed"; "pending" won't work -- it just sets a timeout period and then deletes the message.
  • A way to tag a tracker item by the relevant documentation section (e.g. language reference, library reference, etc.)
  • The ability to participate in a bug discussion through email instead of the web interface
  • The ability to define a filter on tracker items so that you can be emailed when a new tracker item meets your criteria
  • A way to identify relations between bugs, e.g. this bug closes another bug.
  • The ability to close a bug with a checkin.

A Call for Trackers was to be soon forthcoming.

Contributing threads:

Making decorated functions easier to introspect

Nick Coghlan offered to add a function to the new functools module to make writing introspectable decorators easier. Many decorators that return new functions look something like:

def decorator(func):
    def new_func(*args, **kwargs):
        ...
    return new_func

But the newly created function metadata (__name__, __doc__, etc.) is now inconsistent with the original function. Originally, Nick had proposed introducing a decorator function to do this, but he settled instead on a simple helper function, functools.update_wrapper, which can be called by decorator writers to update the appropriate metadata.

Contributing thread:

Tkinter hangs due to Tk bug

Thomas Wouters noticed that test_tcl locked up when Tcl and Tk were compiled with --enable-threads and he tried to refleaktest Tkinter. Seems that despite the lack of any note in the Tk documentation, Tk_Init() doesn't like being called twice even when the first call results in an error. Martin v. Löwis reported the bug to the Tk folks and added a workaround for the current behavior.

Contributing thread:

Deferred Threads

Previous Summaries

Skipped Threads

Epilogue

This is a summary of traffic on the python-dev mailing list from April 16, 2006 through April 30, 2006. It is intended to inform the wider Python community of on-going developments on the list on a semi-monthly basis. An archive of previous summaries is available online.

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