you forgot that counting starts at 0 so its 0-99 and not 1-100.
The 100th element is at string.printable[99]
EDIT: assuming you want to loop around, you should use the modulus operator %
so to access the 100th item in a 100 item list you would do:
string.printable[99%100]
to get the 180th item in a 100 item list you would do:
string.printable[179%100]
solved Python: How to call index 100