[Distutils] Dynamic linking on Linux, Mac OS, et al

[Phillip J. Eby]

Hi folks.  I just implemented preliminary shared library build support for 
setuptools, but I ran into a bit of a snag.  I was operating under the 
assumption that you could simply put shared libraries in the directory 
alongside the extensions that use them, but in practice it turns out that 
this only works on Windows.  On Linux I found that you could only put 
shared libraries in a directory on LD_LIBRARY_PATH, and I suspect a similar 
issue will be found under OS X and other Unixes.

This seems to be a bit of a problem, in that it appears to mean there's no 
sane way to include shared libraries in an egg on any platform other than 
Windows.  It's common practice for Python extensions built for Windows to 
include shared libraries to avoid having to install them in the Windows 
system directories, but for Unix-like OSes this isn't really the normal 
practice anyway.

But, in the case where a developer wants to include a shared library as 
part of the distribution, this remains somewhat problematic.  One can of 
course install the library to a platform-appropriate location ($prefix/lib 
on most platforms), but to do it from an egg is harder.  You can't simply 
unzip the egg any more, you would have to also move the libraries to a 
standard installation location, breaking any hope of multi-version 
support.  (And this would have to be able to happen on the fly, when shared 
libraries and extensions are extracted to the cache directory, if running 
zipped.)

I don't suppose you can modify LD_LIBRARY_PATH on the fly?  Any other 
options?  Should I just give up on supporting shared libraries on anything 
but Windows, perhaps silently converting the shared libraries to static ones?