I have written a python package that requires the following to be installed:
numpy, matplotlib, graphviz

Now I want numpy and matplotlib to be definitely available for the package to work but graphviz is not a strict requirement. It is needed only for some specific functionality.

How do I configure my requirements.txt and my setup.py to make sure that during pip installation of my package, even if installation of graphviz fails the rest of the package is installed correctly.

That is, I am ok with this one specific functionality of graphviz to not be available but I want the package to be installed definitely and serve most of its purpose.