Added exercise 8

ex_08.py

@@ -0,0 +1,38 @@
+#!/usr/bin/python3
+
+from itertools import count
+import random
+
+from util.io import readvalue
+
+def peter_coin_series(randf = random.randint):
+	result = 0
+
+	for k in count(1):
+		if(randf(0, 1) < 0.5):
+			return (result, k)
+		result += 2**k
+
+
+
+if( __name__ == "__main__"):
+	
+	def positive_int(s):
+		i = int(s)
+		if(i <= 0):
+			raise ValueError("{} is negative".format(i))
+		return i
+
+	print("I am going to toss a coin many times.\n" 
+		"You are going to win 2**k if no head appears afer k throws.\n")
+
+	bet = readvalue("How many ducats do you want to bet? ", positive_int)
+	result, throws = peter_coin_series()
+
+	win = bet - result
+
+	if(win < 0):
+		print("Bad, A head came out on throw #{}. You lost {} ducats.".format(throws, -win))
+	else:
+		print("You won {} ducats.".format(win))
+