"RuntimeError: Make sure the Graphviz executables are on your system's path" after installing Graphviz 2.38
You should install the graphviz package in your system (not just the python package). On Ubuntu you should try:
sudo apt-get install graphviz
import os
os.environ["PATH"] += os.pathsep + 'D:/Program Files (x86)/Graphviz2.38/bin/'
In windows just add these 2 lines in the beginning, where 'D:/Program Files (x86)/Graphviz2.38/bin/' is replaced by the address of where your bin file is.
That solves the problem.
This one solved the problem for me on MAC:
brew install graphviz