Using pkg_resources is probably better if it works -- zope.interface doesn't have a __version__ attribute that we can query, but pkg_resources knows zope.interface's version number, for one thing.
This code falls back to the old way -- looking at the __version__ attributes and __file__ attributes -- if the pkg_resources way doesn't answer.
Note that this patch also changes the capitalization of "Nevow", "Twisted", and "pyOpenSSL", and the spelling of "allmydata-tahoe". These changes are not frivolous: they are reflecting the fact that we are naming Python packages (technically called Python "distributions") instead of Python modules (technically and confusingly called Python "packages") here. The package ("distribution") is named "allmydata-tahoe". The module ("package") is named "allmydata".
That's the version of simplejson that comes with ubuntu feisty, and the one that we've required for most of our history. Currently the Ubuntu dapper buildslave fails (see issue #534), and setting the simplejson requirement to be >= 2.0 would fix that failure, but I don't understand why.
We'll see if this fixes the tests on all of our current buildslaves, and if it does then I'll be happy to leave it at "> 1.8.1" for now, even though I don't know exactly what versions of simplejson changed exactly what behavior that interacts with exactly what environment. See http://allmydata.org/trac/tahoe/ticket/534 for uncertainties.
In the near future we might start actually relying on setuptools's pkg_resources's "require()" function to make modules importable, so we can't just skip zope.interface.
This causes a problem on debian sid, since the pyOpenSSL v0.6 .deb doesn't come
with .egg-info, so setuptools will not know that it is already installed and
will try to install pyOpenSSL, and if it installs pyOpenSSL v0.7, then this
will trigger the bug in Twisted v8.1.0 when used with pyOpenSSL v0.7.
http://twistedmatrix.com/trac/ticket/3218
Now the comments in twisted #3218 suggest that it happens only with the select
reactor, so maybe using --reactor=poll will avoid it.
Remove docs/install-details.html and README.win32 for now (see #282).
Remove checks for pywin32 and pyopenssl in Makefile -- that is (or will be) automated by setuptools.
Remove twisted from setup_requires. This causes the problem in which Nevow doesn't declare its dependency on Twisted (#440) to yield a clear ImportError mentioning Twisted and to fail repeatedly, rather than yielding a weird ImportError and working on the second identical attempt.
Fix Makefile to set PATH so that trial and twistd can be found by "make test" after Twisted was installed into support/ during "make"
This happens to work, because all of our "distribution" (i.e. distributable packaged Python code) names to coincide with all of their "package" (i.e. a directory with a __init__.py in it, which is "import"-able) names, except, I think for Twisted on Brian's debian sid system.
But there's no reason why it should always work, and the only reason for that __import__() was to give us an explicit error message indicating missing requirements in the case that pkg_resources isn't importable or that the requirements don't have correct .egg-info metadata. So, by removing this stanza we may allow certain places to get a more ad-hoc failure message, i.e. an ImportError from somewhere, instead of an ImportError from _auto_deps.py, but that's okay.
Note that dependencies which do not have their .egg-info metadata with them are increasingly rare, since Python 2.5 distutils creates the .egg-info file by default, and Linux distributions have stopped their former practice of actively deleting the .egg-info files.
We've never heard of a version of zope.interface that *wasn't* compatible, and there is a bug in Ubuntu's packaging of zope.interface which causes it to report its version number as 0.0.0:
https://bugs.launchpad.net/zope.interface/+bug/185418
