Returning A Numpy Matrix?

So what I'm trying to do is create a function that'll throw 2 dice n times. For every throw, if at least one dice number is odd, we'll return the sum of the pair's values, if not w

Solution 1:

As you are creating a numpy array of the correct size you don't need to append values to it. Instead you need to fill the array with values. For example:

rolls = np.zeros(shape=(2, 3))
# [[ 0.  0.  0.]
#  [ 0.  0.  0.]]

rolls[1,:] = 1,2,3
# [[ 0.  0.  0.]
#  [ 1.  2.  3.]]

Another thing to note is that your if statements are not doing what you think they are. See this question for a good explanation.

So, for your example you would want to do

defdice(n):
    rolls = np.empty(shape=(n, 3))

    for i inrange(n):
        x = random.randint(1,6)
        y = random.randint(1,6)

        if {x, y} & {1, 3, 5}:  # Suggested by Elazar in the comments  # if x in [1,3,5] or y in [1,3,5]:  # Another way to do it      
            sum_2_dice = x + y
            rolls[i,:] = x, y, sum_2_dice

        else:
            sum_2_dice = 0
            rolls[i,:] = x, y, sum_2_dice

    return rolls

If you have to return a matrix (I don't think there is any benefit) you can simply convert it when you return the value:

return np.matrix(rolls)

You can check the type of the output by doing:

result = dice(2)

print (type(result))
# <class 'numpy.matrixlib.defmatrix.matrix'>