//script.sh
function run_ffmpeg() {
    url=$1
    duration=`ffprobe $url | grep "Duration"`
    $out=_$duration"_`echo $url | sed "s/.*\///g" | sed "s/\.mp4.*/.jpg/g`

    ffmpeg -i $url -vf "select='eq(n,LAST_FRAME_INDEX)'" -vframes 1 $out
}

run_ffmpeg $1

=================

// script.py
res = subprocess.run("bash script.sh %s" % url, shell=True, stdout=subprocess.PIPE)