Matrix times Vector

Write a Python function that takes the dot product of a matrix and a vector. return -1 if the matrix could not be dotted with the vector

Example:

Input:

a = [[1, 2],[2, 4]], b = [1, 2]

Output:

[5, 10]

Reasoning:

1*1 + 2*2 = 5; 1*2+ 2*4 = 10

Code:

import numpy as np

def matrix_dot_vector(a, b):
    a = np.array(a)
    b = np.array(b)

    if a.shape[1] != b.shape[0]:
        return -1

    return np.array(a) @ np.array(b)