Folks:
I have a recurring problem with distutils/setuptools/Distribute,
which is that I don't know how to extend the functionality of
setup.py and make the new functionality be testable and modular.
Here's one specific example that I currently have a lot of experience
with: I'd like to generate a version number from revision control
history. Don't get hung up on the desired functionality though -- if
you think that generating version numbers is best done a different
way, or if you don't care about generating version numbers, then
please just mentally insert some other extension of your build
functionality that you do care about.
I'm familiar with three different ways to implement an extension like
this.
The first is what Nevow does [1], which is to write in setup.py "from
nevow import __version__". Well, this works in the case that
setup.py is being executed as the command-line script in a fresh,
empty Python interpreter, but it fails in the case that the Python
interpreter has already been running for a while, has already
imported nevow (a *different* nevow from a different location on the
local filesystem), and is now importing *this* nevow's setup module
in order to build this nevow. This happens with setuptools and
py2exe. Distribute v0.6 includes a patch [2] to fix this, but I'm
not sure the patch is right (it involves 'for m in various_modules:
del sys.modules[m]' and it doesn't seem to fix all cases). PJE says
"Thou shalt not import yourself when trying to build yourself" [3].
Glyph says "Then how do I test this code?" [4]. I say "Ugh, I don't
know. Let's look at the other two ways to do it."
The second is what I do in some of my packages such as pycryptopp
[5]. Just take that functionality that you want to add to all of your
packages and cut and paste the code into each of your setup.py's,
then edit it a little to reflect the correct name of the current
package. This sucks because you're cutting and pasting code, because
your setup.py gets bigger and hairier the more functionality your
build system has, and because, again, you can't test it.
The third is what I do in Tahoe-LAFS [6]. I moved the functionality
in question into a separate Python package, in this case named
"darcsver" [7], and used setuptools's plugin system to add a command
named "darcsver" which initializes the distribution.metadata.version
attribute correctly. Then I had to add a bunch of aliases to my
setup.cfg [8] saying "If you're going to build, first darcsver, and
if you're going to install, first darcsver, and ...". This sort of
works, except that yesterday my programming partner Brian Warner
informed me [9] that he expected the "python ./setup.py --version"
command-line to output the version number. Argh! There is no way to
configure in my setup.cfg "If you're going to --version, first
darcsver.".
So it appears to me that none of these techniques are both modular/
testable and compatible with distutils/setuptools/Distribute. What
are we to do?
Regards,
Zooko
[1] http://www.divmod.org/trac/browser/trunk/Nevow/setup.py?rev=17531
[2] http://bugs.python.org/setuptools/issue20
[3] http://bugs.python.org/setuptools/msg139
[4] http://www.divmod.org/trac/ticket/2699#comment:20
[5] http://allmydata.org/trac/pycryptopp/browser/setup.py?rev=661#L181
[6] http://allmydata.org/trac/tahoe/browser/setup.py?rev=4036#L97
[7] http://allmydata.org/trac/darcsver
[8] http://allmydata.org/trac/tahoe/browser/setup.cfg?rev=3996#L46
[9] http://allmydata.org/trac/darcsver/ticket/6
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