import numpy as np
from matplotlib.pyplot import plot, show 

cash = np.zeros(10000)
cash[0] = 1000
outcome = np.random.binomial(9, 0.5, size=len(cash))

for i in range(1, len(cash)):

   if outcome[i] < 5:
      cash[i] = cash[i - 1] - 1
   elif outcome[i] < 10:
      cash[i] = cash[i - 1] + 1
   else:
      raise AssertionError("Unexpected outcome " + outcome)

print outcome.min(), outcome.max() 

plot(np.arange(len(cash)), cash)
show()