headtails.py

import random

def tosses_until(s):
    tosses = ''
    while not tosses.endswith(s):
        tosses += random.choice('HT')
    return len(tosses)

TRIALS = 10000

alice = sum(tosses_until('HT') for i in range(TRIALS))
bob = sum(tosses_until('HH') for i in range(TRIALS))

print("Alice: %d / %d " % (alice, TRIALS))
print("  Bob: %d / %d " % (bob, TRIALS))

"""
$ python headtails.py 
Alice: 40062 / 10000 
  Bob: 59274 / 10000 
$ python headtails.py 
Alice: 39892 / 10000 
  Bob: 60868 / 10000 
$ python headtails.py 
Alice: 40259 / 10000 
  Bob: 60975 / 10000 
$ python headtails.py 
Alice: 39743 / 10000 
  Bob: 59394 / 10000 
$ python headtails.py 
Alice: 40209 / 10000 
  Bob: 60172 / 10000 
$ python headtails.py 
Alice: 39914 / 10000 
  Bob: 59943 / 10000 

"""