transform 1d array to a 2d matrix (cagie coding challenge)

# import numpy as np


def make_matrix(array, row_count, column_count):
    # make sure dimensions valid
    if row_count * column_count != len(array):
        raise ValueError("Invalid matrix size: dimensions are invalid")

    ret = []
    idx = 0 
    for i in range(row_count):
        a_row = []
        for j in range(column_count):
            a_row.append(array[idx])
            idx = idx + 1

        ret.append(a_row)

    return ret

    # return array.reshape(n, m)


if __name__ == "__main__":

    # using NumPy to help transform numbers if you do maths stuff
    # arr = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12])

    # vanilla stuff
    arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

    my_matrix = make_matrix(arr, 3, 4)

    print(f"Original flat(1 dimension) matrix was: {arr}\n")
    print(
        f"Function make_matrix instructed with n and m values made this matrix:\n {my_matrix}")