[Python-Dev] Sharing expat instances

["Martin v. Löwis"]

Phillip J. Eby wrote:
> I don't know.  I can see that the split makes sense for prefix/exec-prefix 
> distinctions, but then again, the disutils will install an entire 
> distribution in exec-prefix if it contains "impure" parts, so that's 
> certainly an option here.
> 
> On the other hand, it's not clear to me *why* the lib-dynload/DLLs 
> directories exist, since it seems to me that that's what exec-prefix is 
> for.

Can you please explain? exec_prefix will point to, say,
/usr/i686; it shouldn't be that .so files are directly installed in
that location. Instead, Python searches them in
EXEC_PREFIX "/lib/python" VERSION "/lib-dynload".

> Perhaps somebody can explain why lib-dynload/ and DLLs/
> exist?

To have a directory on sys.path where native modules are found.

> Perhaps some platforms have to add these directories to some 
> godforsaken environment variables like LD_LIBRARY_PATH or something?

Not to my knowledge, no. lib-dynload was introduced in revision 8976,
where it was renamed from "/sharedmodules". This, in turn, was
introduced into getpath.c in revision 7775 (and 7776). It was added to
Modules/Setup.in in revision 6313, and to Makefile.in in 6321.
Unfortunately, the checkin message of 6321 only says

  More changes to install targets.

The notion of a separate makefile variable for shared libraries
goes back to Modules/Makefile.pre.in at 4333, which first introduced
dynamic loading (in 1994).

Regards,
Martin