matplotlib - Plotting 3D Polygons in Python 3

Question

In my quest to somehow get 3D polygons to actually plot, I came across the following script (EDIT: modified slightly): Plotting 3D Polygons in python-matplotlib

from mpl_toolkits.mplot3d import Axes3D
from matplotlib.collections import Poly3DCollection
import matplotlib.pyplot as plt
fig = plt.figure()
ax = Axes3D(fig)
x = [0,1,1,0]
y = [0,0,1,1]
z = [0,1,0,1]
verts = [zip(x, y,z)]
ax.add_collection3d(Poly3DCollection(verts),zs=z)
plt.show()

But when I run that, I get the following error message:

TypeError: object of type 'zip' has no len()

It seems that this may be a Python 2 vs. 3 thing, as I am running in Python 3, and that post is five years old. So I changed the third-to-last line to:

verts = list(zip(x, y, z))

Now verts shows up in the variable list, but I still get an error:

TypeError: zip argument #1 must support iteration

What? How do I fix this?

Answer 1

I've had a similar problem with the zipping. I support the thesis it is a python 2.x vs 3.x thing.

However, I've found somewhere that apparently works:

from mpl_toolkits.mplot3d import Axes3D
from mpl_toolkits.mplot3d.art3d import Poly3DCollection
import matplotlib.pyplot as plt

fig = plt.figure()
ax = Axes3D(fig)
x = [0, 1, 1, 0]
y = [0, 0, 1, 1]
z = [0, 1, 0, 1]
verts = [list(zip(x, y, z))]
print(verts)
ax.add_collection3d(Poly3DCollection(verts), zs='z')
plt.show()

I've thus made two changes:

1. replaced the line: from matplotlib.collections import Poly3DCollection by: from matplotlib.mplot3.art3d import Poly3DCollection.

   I don't know where your import statement originates from, but it didn't seem to work for me

2. changed the line: verts = list(zip(x,y,z)) to verts = [list(zip(x, y, z))]

Somehow, the latter seems to work. Having just started myself with python, I cannot offer an iron-clad explanation. However, here goes nothing: the class Poly3DCollection requires as the first input parameter a "collection", hence a list of lists. In this case, only list is given, which is assumed thus missed a level. By adding another level to it (via the [...]) it worked.

I've got no idea if this explanation makes sense, however it fits intuitively to me ;)

These modifications seem to work, as this code creates the desired 3D polygon (I've noticed that since this is my first post, I'm not allowed to post a proof-of-the-pudding figure.... )

hope this was useful,

kind regards