On Mon, 14 Sep 2009 07:13:55 -0700, Glyph Lefkowitz <glyph@twistedmatrix.com> wrote:
So you can for example define a list of dependencies that changes wether
you are under windows or linux, etc..
OK. I've never had that situation. I'm sure someone has, but it doesn't see common.
Twisted actually has this. On Windows, we need pywin32 to implement many of the features which can be implemented with just the stdlib on Posix. But this is the only thing I can imagine computing based on the execution environment.
I believe virtualenv requires pywin32. Maybe several other Python packages too.
I may be missing some context, but I did about an hour of googling around before responding here, and for the life of me I can't find a simple answer to the question: how do I currently programatically get the metadata out of a distribution?
http://pypi.python.org/pypi/pkginfo/
[...] Before adding conditional support to setup.cfg I would want to have a separate 'metadata.py' whose responsibilities were clearer: just produce the metadata, don't do any pre-build steps. Ideally that would be easy to load correctly from setup.py as well.
I double users would follow this proposed convention. Once in a while, I stumble upon Python packages that do not even succeed at the "python setup.py" stage. Even if they did, what prevents them from making metadata.py a little more sophisticated so as to introduce inadvertent bugs on other platforms? (Just today, argparse's new release broke on linux and mac, but not on Windows .. due to regex parsing behavior) I vote for static metadata anyday.
Inspecting metadata could also be made easier by having an API more like this for setup.py:
d = Distribution(... metadata ....) if d.installing: my_project.custom_prepare_for_build() d.setup()
since you can't really tell what setup() is going to do until you've already called it.
I doubt this would happen in practice even if widely suggested by distutils/setuptools.
So finally, if there's still no standard programmatic way to get at the distribution metadata after setup.cfg is modified to have conditional expressions in it, what exactly is the point?
... Conditional metadata for Python versions does not have to be very complicated in my opinion. Simply have the following in setup.cfg, and thus in PKG-INFO: install_requires = ['lxml', 'multiprocessing[pyver<(2,6)]', 'argparse', 'pywin32[platform.name=windows]']
metadata.get_install_requires(for_pyver=(2,6), platform=Platform(name='windows', arch='x86')) ['lxml', 'argparse', 'pywin32']
I don't imagine fields other than `install_requires` to vary based on the target environment. Simple, no? -srid