There are two things need to be modified when a third party tool function is used in the MATLAB Function Block:
(1) Using coder.extrinsic
In Simulink, when you have a MATLAB function block, in order to have it to be integrated with Simulink, this MATLAB function block needs to be compile to have a MEX file. This is not an issue for any in-house MATLAB command. However, for a python function, it becomes an issue since the engine does not know how to MEX the .py code. As the error message suggested, you can consider to use 'coder.extrinsic' to tell the MATLAB Function block not to MEX certain line of code with Python. In this way, that line of code will be dispatched to and executed inside the MATLAB environment, and not the Simulink environment. Here is the documentation about this function.
(2) Preinitialize the variable to which it is assigned.
Wrap the whole script to a M-function and just call it once inside the MATLAB Function Block:
This way, all the internal Python will be calculated in the MATLAB engine and only the output y is used in the Simulink simulation.
Here is a similar case using MATLAB Function block, same workflow, the only difference is the third party tool
