Trying to cycle through a list of charcters

[pooky2483]

When I said shorten it, I meant the whole length of uppercase, lowercase, numbers and -_
'-_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
out of all the characters above, using a length of 22, cycle through the above string.

Any better?