[Distutils] setup_requires not caching downloaded packages?

[Zooko Wilcox-O'Hearn]

Barry:

What is the download cache?

I have a guess.  If you are installing with the setuptools "install"  
command, then the things which are "install_requires" get installed  
into some target location, but things which are build_requires get  
installed into the PWD.  (If you don't specify a target, then it is  
the system site-packages.  In my build system [1], we typically don't  
use "install" and instead use "develop" with a --prefix argument  
which specifies the target.  I assume virtualenv does something  
similar.)

Therefore, a later build will have its install_requires already  
satisfied (if it is using the same installation target), but its  
build_requirements will not be satisfied.

If that's what's going on then a solution might involve pre- 
installing setuptools_bzr onto the build system, or patching  
setuptools to specify a location for build requirements and re-using  
that location.

Regards,

Zooko

[1] http://allmydata.org/trac/tahoe/browser/setup.cfg