Answer of Probabilistic Robotics Exercise 2-2

2_2.py

#!/usr/local/bin/python
import random
import collections

(
  Sunny,
  Cloudy,
  Rainy,
) = range(0, 3)

Weather = ["Sunny", "Cloudy", "Rainy"]

def genWeather(today):
  tomorrow = 0
  rnd = random.random()
  if today == Sunny:
    if rnd < 0.8:
      tomorrow = Sunny
    else:
      tomorrow = Cloudy
  elif today == Cloudy:
    if rnd < 0.4:
      tomorrow = Sunny
    elif rnd < 0.8:
      tomorrow = Cloudy
    else:
      tomorrow = Rainy
  else: # today == Rainy
    if rnd < 0.2:
      tomorrow = Sunny
    elif rnd < 0.8:
      tomorrow = Cloudy
    else:
      tomorrow = Rainy
  return tomorrow

if __name__ == '__main__':
  aryWeather = []

  today = Sunny
  for i in range(0, 100000):
    tomorrow = genWeather(today)
    aryWeather.append(tomorrow)
    today = tomorrow

  cnt = collections.Counter(aryWeather)
  for k, v in cnt.items():
    print Weather[k], v, v/100000.