python can compile in two modes, normal and optimized. in optimized 
mode, the read-only builtin variable __debug__ will be set to 0, and 
thus code fragments like this:

if __debug__:
     print "there are %d eggs in the basket now." % (eggs)

will be optimized away.

is there similar thing in ruby? or do i have to use a preprocessor?

-- 
dave