I have successfully installed Graphviz tool from http://graphviz.org, updated my PATH variable appropriately and can generate .PNG files using Python module Graphviz with WinPython 3.6.1. However, I cannot get anywhere using the pydot V1.2.3 module in the same environment. 

The online help suggests that there there are write & write_png members but I can find no trace of them. My sample script is attached. The error I get is:

Traceback (most recent call last):
  File "ML_ex2.py", line 109, in <module>
    graph.write(path=out_fn, format="png")
AttributeError: 'list' object has no attribute 'write'