simulating rolling 2 dice in Python

Question

I have been asked to simulate rolling two fair dice with sides 1-6. So the possible outcomes are 2-12.

my code is as follows:

def dice(n):
    x=random.randint(1,6)
    y=random.randint(1,6)
    for i in range(n):
        z=x+y
    return z

My problem is that this is only returning the outcome of rolling the dice 1 time, so the outcome is always 2-12. I want it to return the sum of rolling the dice (n) times.

Does anyone have any suggestions for me?

Answer 1

Roll the dice in the loop:

import random

def dice(n):
    total = 0
    for i in range(n):
        total += random.randint(1, 6)
    return total

The += augmented assignment operator basically comes down to the same thing as total = total + random.randint(1, 6) when summing integers (it is slightly more complicated than that, but that only matters for mutable objects like lists).

You could even use a generator expression and the sum() function:

def dice(n):
    return sum(random.randint(1, 6) for _ in range(n))

This basically does the same thing as the for loop in the first example; loop n times, summing up that many random numbers between 1 and 6 inclusive.

If instead of rolling n times, you need to produce n results of 2 dice rolls, you still need to roll in the loop, and you need to add the results to a list:

def dice(n):
    rolls = []
    for i in range(n):
        two_dice = random.randint(1, 6) + random.randint(1, 6)
        rolls.append(two_dice)
    return rolls

This too can be written out more compactly, with a list comprehension:

def dice(n):
    return [random.randint(1, 6) + random.randint(1, 6) for _ in range(n)]

You could also use random.choice() from a list of generated sums; these are automatically weighted correctly; this basically pre-computes the 36 possible dice values (11 unique), each with equal probability:

from itertools import product

two_dice_sums = [a + b for a, b in product(range(1, 7), repeat=2)]

def dice(n):
    return [random.choice(two_dice_sums) for _ in range(n)]

Either way, you'll get a list with n results:

>>> dice(5)
[10, 11, 6, 11, 4]
>>> dice(10)
[3, 7, 10, 3, 6, 6, 6, 11, 9, 3]

You could pass the list to the print() function to have these printed on one line, or on separate lines:

>>> print(*dice(5))
3 7 8 6 4
>>> print(*dice(5), sep='\n')
7
8
7
8
6