Python 'while' with two conditions: "and" or "or"

Question

This is a very simple dice roll program that keeps rolling two dice until it gets double sixes. So my while statement is structured as:

while DieOne != 6 and DieTwo != 6:

For some reason, the program ends as soon as DieOne gets a six. DieTwo is not considered at all.

But if I change the and to an or in the while statement, the program functions perfectly. This doesn't make sense to me.

import random
print('How many times before double 6s?')
num=0
DieOne = 0
DieTwo = 0

while DieOne != 6 or DieTwo != 6:
    num = num + 1
    DieOne = random.randint(1,6)
    DieTwo = random.randint(1,6)
    print(DieOne)
    print(DieTwo)
    print()
    if (DieOne == 6) and (DieTwo == 6):
        num = str(num)
        print('You got double 6s in ' + num + ' tries!')
        print()
        break

Solution 1

TLDR at bottom.

First off, while loops run if the following condition is true, so

DieOne != 6 or DieTwo != 6:

must return true when simplified, for the while funtion to run

The and operator returns true if both conditions are true, so the while loop will only run when it is True and True.

So the following won't run if either of the dice rolled a 6 for example:

while DieOne != 6 and DieTwo != 6:

If DieOne rolled a 4 and DieTwo rolled a 6, the while loop won't run because DieOne != 6 is true, and DieTwo != 6 is false. I put this train of thought into code below.

while DieOne != 6 and DieTwo != 6:
while True and False:
while False: #So it won't run because it is false

The or operator works differently, the or operator returns true when one of the conditions is true, so the while loop will run when it is True or True, True or False, or _False or True. So

while DieOne != 6 or DieTwo != 6:

will run if only either dice rolled a six. For example:

If DieOne rolled a 4 and DieTwo rolled a 6, the while loop will run because DieOne != 6 is true, and DieTwo != 6 is false. I put this train of thought into code below.

while DieOne != 6 or DieTwo != 6:
while True or False:
while True: #So it will run because it is true

TLDR/Review:

while True: #Will run
while False: #Won't run

And:

while True and True: #Will run
while True and False: #Won't run
while False and True: #Won't run
while False and False: #Won't run

Or:

while True or True: #Will run
while True or False: #Will run
while False or True: #Will run
while False or False: #Won't run

Solution 2

What you need is Not instead of !=.

try this:

while not (DieOne == 6 or DieTwo == 6):

Comments

[nima]

While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value. You can find more information on how to write good answers in the help center: stackoverflow.com/help/how-to-answer . Good luck 🙂

[ghulseman]

Good try, but this runs into the same problem as my original code. It works if you change the Or operator to And.