ImportError: No module named mpl_toolkits
I solved this by running the following imports in the following order:
import matplotlib.pyplot as plt 
import mpl_toolkits
from mpl_toolkits.mplot3d import Axes3D
Note: This only worked for me on python3. So first, I had to install python3 and pip3. Then I did "pip3 install matplotlib" in Terminal. If you already have matplotlib then try "pip3 install --upgrade matplotlib"
I have a python program and am trying to plot something using the mplot3d from mpl toolkits,  but whenever I try to import the Axes3D from mpl_toolkits from mpl_toolkits.mplot3d import Axes3D
 I get the following error: ImportError: No module named mpl_toolkits