Recommendations:

1. Install graphviz package to use 'dot' functionalities. More about this : https://www.howtoinstall.co/en/ubuntu/xenial/graphviz

2. doxygen has limited functionalities for python documentation. To have more detailed documentation for Python please follow

https://github.com/Feneric/doxypypy

and install doxypypy. Also create "py_filter.sh" in the current ('documents') folder.