winstay

Use rpsrunner.py to play unranked matches on your computer.

Source code:

import random
last = random.choice(["R","P","S"])
if input == "R":
	if last != "P":
		last = random.choice(["R","S"])
elif input == "P":
	if last != "S":
		last = random.choice(["R","P"])
	output = last
elif input == "S":
	if last != "R":
		last = random.choice(["P","S"])
output = last