st.petersburg paradox in python

manpreet Best Answer 3 years ago

I have been trying to do the St.Petersburg paradox( the player wins 2 dollars if tail appears on the first toss, 4 dollars if heads appear on the first toss and tails on the second, 8 dollars if heads appear on the first two tosses and tails on the third, and so on.) in python.

But I cannot do it correctly. I want to know if we flip the coin 100 times, how much money we will get.

import random

def St(number):

    l=[]

    money=0

    signs=["head","tail"]

    for i in range(number):

        choices=random.choice(signs)

        while choices=="head":

            l.append(2)

        if choices=="tail":

            money=money+sum(l)+2

            del l[:]

    result=round(money/number,3)

    return(money,result)

print(St(100)) 

but it doesnt give any results or just 2 i tried in another way but its the same: import random

def St(number):

    l=[]

    money=0

    signs=["head","tail"]

    for i in range(number):

        choices=random.choice(signs)

        while choices=="head":

            l.append(choices)

        if choices=="tail":

            money=money+2**(len(l)+1)

            del l[:]

        result=round(money/number,3)

        return(money,result)

print(St(100)) 

Can you help me?

manpreet 3 years ago

In Python, there's usually an easy way. Here's what you could do, using the U(0,1)-sampling numpy.random.random:

from numpy.random import random

def St(number):

  result = 2

  for i in range(number):

    if random() < 0.5: return result

    result *= 2

  return result