direct execution of python scripts Code Answer

I have noticed that sometimes python scripts are not being started directly, ie /foo/bar.py, but rather from a shell script, which does nothing else than /usr/bin/python -O /foo/bar.py $@

One such example is wicd network manager. /usr/bin/wicd-gtk is a shell script, which starts the wicd-client.py:

$ cat /usr/bin/wicd-gtk

exec /usr/bin/python -O /usr/share/wicd/gtk/wicd-client.py $@

What is the purpose of this extra step?

What would be the difference if I started /usr/share/wicd/gtk/wicd-client.py directly (provided it is executable) ?

Answer

You didn’t post the full script — the script does other things before running wicd-client.py. It first ensures that a certain directory and a certain symbolic link exist:

# check_firstrun()
if [ ! -d "$HOME/.wicd" ]; then
    mkdir -p "$HOME/.wicd"
fi
# Make sure the user knows WHEREAREMYFILES ;-)
if [ -e "/var/lib/wicd/WHEREAREMYFILES" ] && [ ! -L "$HOME/.wicd/WHEREAREMYFILES" ]; then
    ln -s "/var/lib/wicd/WHEREAREMYFILES" "$HOME/.wicd/WHEREAREMYFILES"
fi

Then it runs Python with the -O option, which causes it to optimize the bytecode. I don’t know how useful that is.

The wrapper script also forces /usr/bin/python to be used, whereas /usr/share/wicd/gtk/wicd-client.py starts with #!/usr/bin/env python, so it picks up whichever python comes first in the command search path. On most systems this won’t make any difference.

Note that there’s a bug in this script: $@ should be "$@". The wrapper script will fail if any argument contains whitespace or wildcard characters [*?.

You could safely run /usr/share/wicd/gtk/wicd-client.py manually, as long as ~/.wicd exists. The Debian package doesn’t make it executable, though; maybe other distributions do.