Numeric array and for loops problem

[Stan]

Thanks's for the replies, I'll keep in mind to check values types.
I'd like to know something more about the technique that Chad exposed
(something like load in memory only some parts of a big array),i saw a
module named arrayfrombuffer wich sould permit to read and write array
directly from files without loading them into memory, but it seems
quite slow. Could someone suggest me some examples ,readings or links!
It would be great! Thanks agian