Integrate a custom .so librarie into a python project

Integrate a custom .so librarie into a python project

I want to integrate a .so librarie into my python project: Here is the
tree: myproject/
__init__.py
core/
__init__.py
mod.py
gui/
__init__.py
mod.py
lib/
test/
main.py
.git
Now I try to integrate a custom library "custom.so" into core
sub-packages. I would like a proper way to integrate it (in the future I'm
going to use a setup.py).