New version released - fixes alot of stuff I had been meaning to fix - namely the insecurities when evaluating function returns. So right now, it can't - paren pairs are stripped from the line. This allows completion to work safely for everything except function/method calls.
I also added argument completion, which works nicely. The following completion chain is after two 'ofu' calls: import rexec x = rexec.RExec() x.c<C-x,C-o> --> x.copy_except(<C-x,C-o> ----> x.copy_except(src, exceptions)
See here: 
Try it out,
let me know what you think. Download link is here:
http://www.vim.org/scripts/script.php?script_id=1542