Linux Keyboard Injector (Python or shell)

I'm wondering if it's possible (and if so, how) to simulate keystrokes on a keyboard using a python or shell script. I'd prefer to not have to download anything or install anything, and just want to have it as a "pure" script. I also would like to avoid ruing the script as the superuser or use 'sudo', but if need be, sudo commands are fine. In addition to injecting text, I would also like to do it in another window (specifically skype, but a general form would be also be appreciated). Sorry if this is too much or nearly impossible with all of my restrictions. Anyways, thanks for any and all feedback.