Coin flip streaks from "Automate the boring stuff with Python"

Question

I am a Python beginner. I'm trying to write a simple but neat code to solve the following problem.

I've written this, but it always evaluates to ~325% somehow. What might be wrong?

import random 
numberOfStreaks = 0 
flip = []
for experimentNumber in range(10000):
# Code that creates a list of 100 'heads' or 'tails' values.

    for i in range(101):    
        flip.append(random.randint(0,1))

# Code that checks if there is a streak of 6 heads or tails in a row.
    for i in flip:
        if flip[i] == flip[i+1]:
            if flip[i] == flip[i+2]:
                if flip[i] == flip[i+3]:
                    if flip[i] == flip[i+4]:
                        if flip[i] == flip[i+5]:
                            numberOfStreaks += 1


    flip = []

print('Chance of streak: %s%%' % (numberOfStreaks / 100))

Your denominator *isn't* 100, it's the number of experiments. That would give you ~3.25%, which is close to the expected value. — jonrsharpe, Apr 07 '20 at 16:12
I've given an answer on a similar thread: https://stackoverflow.com/a/70176317/17555691 — tom_thumb_1, Nov 30 '21 at 21:59

score 0 · Answer 1 · answered Apr 07 '20 at 16:12

This is happening because you are dividing numberOfStreaks by 100 and not the size of the total population.

If you want to get the proportion of streaks that occurred in your sample, then you have to divide the number of successes by the population size.

In other words...

numberOfExperiments = 10000
print('Chance of streak: {}'.format(numberOfStreaks / numberOfExperiments))

score 0 · Answer 2 · answered Jul 01 '22 at 18:34

Solution to coin flip streaks from "Automate the boring stuff with Python"

We won't always get the same result , simply because there is a ton of different combinations for 10000 coin flips , our list will be different each time we run the code, but the percentage of streaks that we will find each time will be around the same. Even the mathematical solution finds an approximate ( won't post it here, too complex and I doubt it will help you)

from random import randint
streak = 0
expList = []
numberOfStreaks = 0
for experimentNumber in range(10000):  # Code that creates a list of 10000 'heads' or 'tails' values.
    if randint(0,1) == 0:
        coin_flip = 'H'
    else:
        coin_flip = 'T'
    expList.append(coin_flip)

for i in range(len(expList)):
        if i==0:
            pass                           # we don't do nothing when i=0 , otherwise we would get an error
        elif expList[i] == expList[i-1]:  # checks if current list item is the same as before
            streak += 1                   # best way I found so we  count 7 Head or Tails in row 
        else:                             # as 1 steak and not 2 
            streak = 0

        if streak == 6:             #checks if there is a streak of 6 heads or tails in a row.
            numberOfStreaks += 1

print (numberOfStreaks)
print('Chance of streak: %s%%' % ((numberOfStreaks / 10000)*100)) # priting and finding percentage of the coin flips that
                                                                 # contain a streak of six heads or tails in a row
                    #probability percentage = ( (no. of successful results) / (no. of all possible results) ) * 100%

Coin flip streaks from "Automate the boring stuff with Python"

2 Answers2