[pkg-boost-devel] Boost.Python: providing libs for both Python 2.4 and 2.5.

[Steve M. Robbins]

Hello,

I wrote about three weeks ago [1] that I'm trying to get Boost's
Python extension helper library building with multiple Python
versions.  Several very helpful suggestions were made, for which I am
grateful.

I have been plugging away, very slowly, ever since.  I'm hoping to
upload it later today and I'd appreciate have some second opinions on
what I've done.

I settled on creating libraries with suffix "-py24" and "-py25" using
the available Boost mechanism of "--buildid" since that ensures the
SONAME also has "-py24" or "-py25".  The shared library files thus
coexist peacefully.

For the link libraries, I chose to retain both the fully-decorated
forms including the "-pyXY" suffix, as well as create symlinks (with
no suffix) for those who just want the default python version.  These
symlinks are maintained by an "rtupdate" script as suggested by a
couple of people.

Focusing only on the simpler, Debian-specific, library names,
the intent is that the following link libraries are availble:

    libboost_python-py24.a -> libboost_python-gcc42-1_34_1-py24.a
    libboost_python-py24.so -> libboost_python-gcc42-1_34_1-py24.so
    libboost_python-py25.a -> libboost_python-gcc42-1_34_1-py25.a
    libboost_python-py25.so -> libboost_python-gcc42-1_34_1-py25.so
    libboost_python.a -> libboost_python-py24.a
    libboost_python.so -> libboost_python-py24.so

The rtupdate script (attached) will replace the last two libraries
with

    libboost_python.a -> libboost_python-py25.a
    libboost_python.so -> libboost_python-py25.so

This allows extension builders to select either the default Python
version, or a specific version, without knowing the Boost
and GCC versions [2].

I'd appreciate any feedback on the above, and especially on what
follows.

I'd love some folks to look over the attached rtupdate script.  My
understanding is that this gets run when the Python default version
changes.  If so, I guess that a bug in the script will cause the
Python package install to fail.  I'd like to avoid the hate mail
generated if that happened; so if you've got a moment, have a look at
the script.

I'd like to ask about intended behaviour if a bad action is supplied.
Or if an unsupported python version is given.  I chose to exit with an
error message and status 1.  Now I'm a little worried that will break
some Python installs and generate the hate mail.  What's the
recommended behaviour here?

Note that my libboost-python-dev postinst script calls it
to populate the symlinks initially:

    /usr/share/python/runtime.d/libboost-python-dev.rtupdate \
    	rtupdate none $(pyversions -d)

I also use it in the prerm to remove all the symlinks:

    /usr/share/python/runtime.d/libboost-python-dev.rtupdate \
    	remove

Thanks,
-Steve


[1] http://lists.debian.org/debian-python/2008/02/msg00033.html
[2] http://lists.debian.org/debian-python/2008/02/msg00045.html
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#! /bin/sh
#
# Update link-library symlinks after a Python default runtime change

set -e

version=1_34_1

die() {
    echo "$@" >&2
    exit 1
}

update_linklibs() {
    py=$1
    suf=$2

    cd /usr/lib
    for thread in "" -mt; do
	for gcc in gcc41 gcc42; do
	    ln -s -f libboost_python-${gcc}${thread}${debug}-${version}-${py}.${suf} \
	             libboost_python-${gcc}${thread}${debug}-${version}.${suf}
        done
	ln -s -f libboost_python${thread}${debug}-${py}.${suf} \
	         libboost_python${thread}${debug}.${suf} 
    done
}

remove_linklibs() {
    suf=$1

    cd /usr/lib
    for thread in "" -mt; do
	for gcc in gcc41 gcc42; do
	    rm -f libboost_python-${gcc}${thread}${debug}-${version}.${suf}
        done
	rm -f libboost_python${thread}${debug}.${suf} 
    done
}

rtupdate() {
    case "$1" in
	python2.4)  py=py24 ;;
	python2.5)  py=py25 ;;
	*)          die $0 unknown python version $1 ;;
    esac

    update_linklibs $py a
    update_linklibs $py so
}

remove() {
    remove_linklibs a
    remove_linklibs so
}


if [ "$1" = "-d" ]; then
    debug=-d
    shift
fi

action="$1"
shift

case "$action" in
    pre-rtupdate)  ;;
    post-rtupdate) ;;
    rtupdate)      rtupdate $1 ;;
    remove)        remove ;;
    *)             die "$0 called with unknown argument '$action'" ;;
esac

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