scram-venv

#!/bin/bash -e

# check for CMSSW environment
if [ -z "$CMSSW_BASE" ]; then
	echo '$CMSSW_BASE not set'
	exit 1
fi

# check for python3 in actual CMSSW area
if ! (cd $CMSSW_BASE && scram tool info python3 >& /dev/null); then
	echo "$CMSSW_VERSION does not provide python3"
	exit 1
fi

# get info from existing python
PYPATH=$(which python3)
PYHOME=$(dirname $PYPATH)
PYVERSION=$(python3 --version | cut -d' ' -f2)
PYVERSHORT=$(echo $PYVERSION | cut -d'.' -f1-2)
PYVERSHORTER=$(echo $PYVERSION | cut -d'.' -f1)
PYNAME=python$PYVERSHORT

# create venv directories
VENVDIR=$CMSSW_BASE/venv/$SCRAM_ARCH
DIRS=(
$VENVDIR \
$VENVDIR/bin \
$VENVDIR/include \
$VENVDIR/lib/$PYNAME/site-packages \
)
for DIR in ${DIRS[@]}; do
	mkdir -p $DIR
done
(cd $VENVDIR; ln -s lib lib64)

# create venv config
cat << EOF > $VENVDIR/pyvenv.cfg
home = $PYHOME
include-system-site-packages = true
version = $PYVERSION
EOF

# link venv executables
EXES=(
python$PYVERSHORTER \
python$PYVERSHORT \
)
for EXE in ${EXES[@]}; do
	ln -s $PYPATH $VENVDIR/bin/$EXE
done

# set up scram hook infrastructure if missing
HOOKDIR=$CMSSW_BASE/config/SCRAM/hooks/runtime
HOOKFILE=${HOOKDIR}-hook
if [ ! -f "$HOOKFILE" ]; then
	mkdir -p $HOOKDIR
	cat << 'EOF' > $HOOKFILE
#!/bin/bash
SCRIPT_DIR=$(dirname $0)
if [ -e ${SCRIPT_DIR}/runtime ] ; then
  for tool in $(find ${SCRIPT_DIR}/runtime -type f | sort) ; do
    [ -x $tool ] && $tool
  done
fi
EOF
	chmod +x $HOOKFILE
fi

# install hook for venv
HOOK=${HOOKDIR}/py3-venv
cat << 'EOF' > $HOOK
#!/bin/bash
echo "RUNTIME:path:prepend:PATH=${LOCALTOP}/venv/$SCRAM_ARCH/bin"
EOF
chmod +x $HOOK

# instructions to activate venv hook and update environment
echo "scram-venv succeeded! please call 'cmsenv' now"

PR opened at cms-sw/cms-common#6

@kpedro88 @smuzaffar This is great! Would be good to have some documentation on how to use it, e.g. somewhere at https://cms-sw.github.io/, now that it's merged.

agree @clelange . @kpedro88 can you please open a PR for https://github.com/cms-sw/cms-sw.github.io/tree/code ?

Will do - after my CHEP plenary today...