from mpl_toolkits.mplot3d import proj3d
import pylab as plt
import numpy as np
import itertools
import math

# the following code snippet should plot a 3D cube, with apparent equal edge lengths
kw_3d = dict(proj_type='ortho', projection='3d', aspect='equal')

_, ax = plt.subplots(subplot_kw=kw_3d)
ax.grid(1)

# draw cube (stackoverflow.com/a/11156353)
r = (-1, 1)
for s, e in itertools.combinations(np.array(list(itertools.product(r, r, r))), 2):
    if abs(s - e).sum() == r[1] - r[0]:
        ax.plot3D(*zip(s, e), c='C0')

# isometric projection (en.wikipedia.org/wiki/Isometric_projection)
ax.view_init(elev=math.degrees(math.atan(1 / math.sqrt(2))), azim=-45)

# annotation
px, py, pz = 1, -1, 1
ax.plot([px], [py], [pz], 'o', ms=10, mfc='none', c='C1')

x, y, _ = proj3d.proj_transform(px, py, pz, ax.get_proj())
xt, yt, _ = proj3d.proj_transform(px, py + .6, pz + .6, ax.get_proj())

ax.annotate('Isometric', (x, y), xytext=(xt, yt), arrowprops=dict(arrowstyle='->'))

plt.savefig('cube.png', dpi=300)