I think Gretl is ignoring the path to Python executable in OS X (El
Capitan). I trying to use a different version of Python (2.7.11) and
Gretl is running the old one (2.7.10) that is supplied by Apple.
I tried three different paths (under GUI "Tools -> Preferences General
(1) "/Applications/Python 2.7/IDLE.app/Contents/MacOS/Python"
(3) "" (empty!)
And executed the following commands: