array([[ a,  b,  c],
       [ 0,  d,  e],
       [ 0,  0,  f]])

def create_upper_matrix(values, size):
    upper = np.zeros((size, size))
    upper[np.triu_indices(3, 0)] = values
    return(upper)

c = create_upper_matrix([1, 2, 3, 4, 5, 6], 3)
print(c)