import random

weeks = 10000 # hardware running time
days_in_week = 7
non_failure_periods = []

#variables to keep track of current hardware state
can_fail = False
error_free_count = 0
days_since_last_failure = 0

for i in range(0, weeks):
	for i in range(0, days_in_week):
		if not can_fail:
			error_free_count += 1
			days_since_last_failure += 1
		if error_free_count > days_in_week: # if error free days have passed, hardware can fail
			error_free_count = 0
			can_fail = True
		if can_fail:
			rand = random.randint(0,6) # Assume 1/7 prob. of failure per day
			if rand == 0: # hardware failure
				non_failure_periods.append(days_since_last_failure)
				days_since_last_failure = 0
				can_fail = False # reboot
			else: # if it didn't fail today, just continue and count
				days_since_last_failure += 1

average = 0
for a in non_failure_periods:
	average += float(a) / float(len(non_failure_periods))

print "Average non-failure period:", average