500yearfloods.py3

#!/usr/bin/env/python3
import random
gaps = []
events = 0
current_gap = 0
for trial in range(1000000):
	if random.random() < (1/500):
		gaps.append(current_gap)
		current_gap = 0
		events += 1
	else:
		current_gap += 1
print(events, '500-year floods')
print(sum(gaps)/len(gaps), 'mean years between 500-year floods')
print(sorted(gaps)[len(gaps)//2], 'median years between 500-year floods')