How to break out of while loop in Python?

Question

I have to make this game for my comp class, and I can't figure out how how break out of this loop.

I have to play against the "computer," by rolling bigger numbers, and seeing who has the bigger score. But I can't figure out how to "break" from my turn, and transition to the computers turn. I need "Q" (quit) to signal the beginning of the computers turn, but I don't know how to do it.

ans = 'R'
while True:
    print('Your score is so far ' + str(myScore) + '.')
    print("Would you like to roll or quit?")
    ans = input("Roll...")
    if ans == 'R':
        R = random.randint(1, 8)
        print("You rolled a " + str(R) + ".")
        myScore = R + myScore
    if ans == 'Q':
        print("Now I'll see if I can break your score...")
        break

Using break the way you are is fine, but you have to type exactly Q. q won't work for example. Is the first line supposed to say ans=('R')? you don't need it anyway — John La Rooy
– John La Rooy, Commented Jan 30, 2013 at 0:28

SabreWolfy · Accepted Answer · 2017-12-02 14:46:08Z

31

A couple of changes mean that only an R or r will roll. Any other character will quit

import random

while True:
    print('Your score so far is {}.'.format(myScore))
    print("Would you like to roll or quit?")
    ans = input("Roll...")
    if ans.lower() == 'r':
        R = np.random.randint(1, 8)
        print("You rolled a {}.".format(R))
        myScore = R + myScore
    else:
        print("Now I'll see if I can break your score...")
        break

edited Dec 2, 2017 at 14:46

SabreWolfy

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answered Jan 30, 2013 at 0:30

John La Rooy

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2 Comments

Learner Over a year ago

Please correct me if needed- break sends a False signal to stop the while loop?

Westcroft_to_Apse Over a year ago

@SIslam Kind of. break stops the while loop, but there isn't a 'False signal': while means 'loop while the expression following the while statement evaluates as True', so if what comes after while is True itself, while will loop forever; break means 'stop looping right now' and works any loop, including both while and for loops.

mkrieger1 · Accepted Answer · 2024-11-11 15:19:42Z

13

I would run the loop until ans is 'Q' like this:

ans = 'R'
while not ans == 'Q':
    print('Your score is so far ' + str(myScore) + '.')
    print("Would you like to roll or quit?")
    ans = input("Roll...")
    if ans == 'R':
        R = random.randint(1, 8)
        print("You rolled a " + str(R) + ".")
        myScore = R + myScore

edited Nov 11, 2024 at 15:19

mkrieger1

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answered Jan 30, 2013 at 0:21

Phil

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Comments

mkrieger1 · Accepted Answer · 2024-11-11 15:22:03Z

9

Don't use while True and break statements. It's bad programming.

Imagine you come to debug someone else's code and you see a while True on line 1 and then have to trawl your way through another 200 lines of code with 15 break statements in it, having to read umpteen lines of code for each one to work out what actually causes it to get to the break. You'd want to kill them...a lot.

The condition that causes a while loop to stop iterating should always be clear from the while loop line of code itself without having to look elsewhere.

Phil has the "correct" solution, as it has a clear end condition right there in the while loop statement itself.

edited Nov 11, 2024 at 15:22

mkrieger1

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answered Jan 30, 2019 at 12:51

Steve Todd

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6 Comments

Missing User Over a year ago

Unless you were using a short example...

stritch000 Over a year ago

Consider rephrasing "Don't use while True and break statements. It's bad programming." While I try to avoid them as a general rule, many times I have simplified logic structures in a while loop simply by using a single break statement. While I agree that 15 break statements scattered through a while loop isn't great, I would posit that neither is 200 lines of code.

Ribo Over a year ago

There are cases where ''while True:' and 'break' are the right thing to do. Sometimes you can't/shouldn't do the 'while' test in the while statement but need to do it within the loop, therefore you need a 'break'

mkrieger1 Over a year ago

@Ribo You can write your own answer. See meta.stackoverflow.com/a/362673

Ribo Over a year ago

I was trying to improve the answer by indicating that there are appropriate cases to use 'while True / break' I think that saying that it is flatly 'bad' is oversimplifying and incorrect. -- expression assignment was an example, there are other operations like '.pop()' that have side effects.

|

mkrieger1 · Accepted Answer · 2024-11-11 15:27:34Z

3

ans = 'R'
while True:
    print('Your score is so far ' + str(myScore) + '.')
    print("Would you like to roll or quit?")
    ans = input("Roll...")
    if ans == 'R':
        R = random.randint(1, 8)
        print("You rolled a " + str(R) + ".")
        myScore = R + myScore
    else:
        print("Now I'll see if I can break your score...")
        ans = False
        break

edited Nov 11, 2024 at 15:27

mkrieger1

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answered Jan 30, 2013 at 0:21

aug2uag

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Comments

DRPK · Accepted Answer · 2021-01-22 05:07:52Z

1

Walrus operator (assignment expressions added to python 3.8) and while-loop-else-clause can do it more pythonic:

myScore = 0
while ans := input("Roll...").lower() == "r":
    # ... do something
else:
    print("Now I'll see if I can break your score...")

answered Jan 22, 2021 at 5:07

DRPK

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