ax = fig.gca(projection='3d')
ax.set_aspect('equal')
MAX = 3
for direction in (-1, 1):
    for point in np.diag(direction * MAX * np.array([1, 1, 1])):
        ax.plot([point[0]], [point[1]], [point[2]], 'w')
установить соотношение сторон 3D-графика matplotlib?