I\'m using python 3.6.3 on a windows 10 machine. I installed pydot and graphviz using pip install via:
py -m pip install pydot py -m pip install grap
Complementing @Ioannis answer, you have to install GraphViz executables via conda (conda install GraphViz).
conda install GraphViz
For my case, after installing GraphViz I tried with the latest pydot (pip install pydot) and the error was resolved.
pip install pydot