[Python-Dev] Issue 4195: Can't execute packages with -m in Python 2.6/3.0

Lisandro Dalcin dalcinl at gmail.com
Sat Nov 22 04:04:19 CET 2008

Unless this is considered a regression...

On Tue, Nov 18, 2008 at 12:51 PM, Guido van Rossum <guido at python.org> wrote:
> I think it crosses the line.
> On Tue, Nov 18, 2008 at 2:55 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> I need a release manager call on whether or not the proposed resolution
>> of this issue goes beyond what is acceptable for a bug fix in 2.6.1.
>> Short version:
>> - Python 2.5 allowed packages to be executed with -m, but in a broken way
>> - I disabled the broken way for 2.6, but didn't provide a replacement
>> - The patch attached to 4195 once again allows execution of packages
>> with -m, but in a clean way similar to the way directories and zipfiles
>> can now be executed
>> - I would like to commit that patch for 3.0/2.6.1, but I'm concerned
>> that it crosses the "no new features" line
>> Long version:
>> There was a bug in python 2.5 that allowed a package name to be passed
>> to the -m switch or runpy.run_module() and it would mostly work.
>> However, the 'mostly' was due to the fact that doing this put the
>> internal import machinery into a slightly inconsistent state: the
>> interpreter was running code from inside a package, but that package
>> wasn't actually present in sys.modules. This could lead to assorted hard
>> to trace import-related weirdness, similar to what you can get when
>> executing a file from inside a package by name. You would often get away
>> with it, but good luck figuring out what is happening if things go wrong
>> (and you aren't already an expert on Python import mechanics).
>> Since the ability to execute packages wasn't intentional, I added the
>> missing check to block it explicitly in 2.6 (but left it alone for 2.5).
>> It seemed like a really niche feature, so I didn't figure out a clean
>> replacement for it at the time.
>> Benjamin noticed this change earlier in the 2.6 release cycle, I pointed
>> out it was a deliberate change, and that's the way it stayed until after
>> 2.6 was released.
>> After the release, Andi Vajda (from the JCC project [1]) contacted me,
>> and together we worked out a better implementation of package support
>> for the -m switch (and runpy.run_module) [2] by extending the
>> __main__.py approach used to support direct execution of zipfiles and
>> directories [3].
>> That's what I would like to add, since it nicely complements the ability
>> to execute zipfiles and directories, while also restoring the ability to
>> pass a package name to the -m switch (but in a way that keeps the import
>> machinery in a consistent state).
>> Cheers,
>> Nick.
>> [1] http://pypi.python.org/pypi/JCC
>> [2] http://bugs.python.org/issue4195 (package execution with -m)
>> [3] http://bugs.python.org/issue1739468 (zipfile execution)
>> --
>> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>> ---------------------------------------------------------------
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> --
> --Guido van Rossum (home page: http://www.python.org/~guido/)
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Lisandro Dalcín
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594

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