PythonExtension | Python extension for NetLogo | Machine Learning library

OK, I made a silly mistake! it seems when defining the PYBIND11_MODULE, the first name, and the name used in setup() need to be the same as the source file, i.e. PythonManager_Pybind11.cpp in my case. This why the linker was complaining about the actual object which was the main source file.
Making these changes, now everything builds just fine.

This is how it looks after these minor changes:

There are two problems here.

First, as far as I can tell, despite being documented, the pip install method really isn't supported, or even expected to work. Kyle Gorman (who I assume is one of the main authors) has commented on multiple forum threads with replies like:

"Using pip for this doesn't make much sense, and that's out of date anyways."

"There's no reason to call pip. The version up there is not compatible with arbitrary OpenFst versions. If you do --enable-python then make and make install, you have already installed pywrapfst for whatever version of OpenFst you're building."

Second, despite saying that it works with "any Python 2.7 or later", it actually only works only with Python 2.7 exactly:

"Before submitting you may want to test Python 3 with the Python extension. We still develop on Python 2.7, exclusively, unfortunately, and it's not tested on Python 3."

And, in fact, that's exactly why your attempt at using --enable-python failed:

I think that you have misunderstood the aim of webservices. We need webservices to make their calls (clients) a platform independent interface which means that once you have created your webservice using any technology (java for your case here) now anyone can call this service by creating a client using any language like python, C#, C++, Ruby, ........... in that case a service which was built by Java will be consumed or called by an application or client created using python and vice versa.