R28 test4. Now works with (and prefers) per user python installations. Expr has also had several big fixes (ternary operator, crashes and so on) so give it a try again. Log, pow and maybe exp is probably not working properly. Everything else should be working though so try it out.
On the positive size Expr can now have up to 26 inputs, x-z, a-w.
Expr correctness and speed comparisons welcome.