[Closed] select vertices in area?

I would like to write as script that can select vertices inside a specified area. I can do it now but I have to check the position of every single vertex in the object to see if it inside that area even if only a few of them are. I need to do this operation several times and things are starting to get pretty slow. I was wondering if there is a faster way of doing this.

Also is there any way to cancel out of a button press operation without using a progress bar?

Thanks in advance,

-bnvm