matrix-multiply.py

a = [[2, 3, 4], [3, 4, 5]]
b = [[4, -3, 12], [1, 1, 5], [1, 3, 2]]

def get_dimension(a):
    if not type(a) == list:
        raise ValueError('Input is not a matrix')

    dim_x = len(a)
    dim_y = len(a[0])

    # Let's check if every elements has the same length
    for x in a:
        if not type(x) == list:
            raise ValueError('Input is not a matrix')

        if not len(x) == dim_y:
            raise ValueError('Input is not a matrix')
    
    return { "x": dim_x, "y": dim_y }


def matrix_multiplication(a, b):
    dim_a = get_dimension(a)
    dim_b = get_dimension(b)

    if (dim_a["y"] != dim_b["x"]):
        raise ValueError('Invalid  matrix dimensions for multiplication')

    c = [ [0]*dim_b["y"] for i in range(dim_a["x"]) ]

    for x in range(dim_a["x"]):
        for y in range(dim_a["y"]):
            for z in range(dim_a["y"]):
                # does not do anything
                c[x][y] = c[x][y] + (a[x][z] * b[z][y])
    return c

print(matrix_multiplication(a, b))