[Distutils] setuptools' "Feature" feature
pje at telecommunity.com
Sat Jul 3 00:18:14 CEST 2010
At 02:29 PM 7/2/2010 -0400, Tres Seaver wrote:
>I haven't found any docs (outside the code) for the
That's because it's essentially deprecated - an experimental thing
that turned out to be, well, a failed experiment.
The problem is that there really needed to be better ways to store
the build state with respect to features, not to mention
distribution-level information about them. So, they only work
correctly if you pass them to *every* setup.py command, while never
changing them. To really work right, there'd need to be a
"configure" command, and some sort of option storage.
And, since most of the *other* use cases for the original features
design were supplanted by "extras" and install_requires, it was
pretty much left to optional C extensions, which might as well be
handled by, well, optional C extensions. ;-)
So, I haven't done anything with features in ages, and didn't
document them because (AFAIK), they were only used by some ancient
packages of my own, such as the original PEAK mega-distribution,
PyProtocols, and RuleDispatch -- mostly to enable or disable various
>- - Feature instances represent optionally-included bits of the
>- - Normally, features are disabled by default, and can be enabled
> by passing '--with-<featurename>' to setup.py.
>- - Features declared as 'standard' are enabled by default, and can be
> disabled by passing '--without-<featurename>' to setup.py.
>- - Features have an 'available' attribute, which can be set to False
> in setup.py to disable a feature based on runtime introspection
> (e.g., using sys.version_info or os.name).
>- - It appears that it should be possible to pass an instance with
> a '__nonzero__' method as the 'available': the code seems only
> to use it in boolean tests.
>- - Features may depend on (force inclusion of) other features.
>- - Enabled features do their actual work by adding **kwargs to
> the args passed directly to setup.py
>- - Distributions created via an invocation to setup.py are not labeled
> in any way to indicate any '--with-<featurename>' (or '--without')
> passed to setup.py during their creation.
>- - There is no way to enable / disable a feature when installing a
> distribution via easy_install.
>The particular use case which led me to investigate Features was easing
>packaging of projects with optional C extensions, such that they could
>be installable on Jython, IronPython, Windows, or GAE. It doesn't seem
>possible to figure out whether a compiler actually exists: jython's
>distutils lies and creates a compiler which raises exceptions, for instance.
Yeah, that's another reason why Features don't even do the optional
compile thing that well. Not Jython specifically, but rather, I
never decided on a good way to handle optional C extensions, that
doesn't involve trapping compilation errors. (I hope distutils2
allows you to declare extensions optional; it's such a common use case.)
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