Import Errors and Undefined Symbols

[benjamin-havens]

I've got a C++ class called MotorInterface stored in MotorInterface.h and MotorInterface.cpp. It is intended to control a group of Maxon EPOS4 motors, which I want to do in some Python code running in ROS. I wrote some binding code and compile it using CMake, and it compiles fine. This is the relevant bits of the CMakeLists.txt:

find_package(pybind11 REQUIRED)
set(PYBIND11_PYTHON_VERSION "3.6.9")
pybind11_add_module(motor_interface src/MotorInterface.cpp src/createPybindings.cpp)

where createPybindings.cpp has the relevant pybind11 code. As I said, this compiles fine and makes a motor_interface.so file.

The problem is, when I try to import, I get several different errors. Using python3 (3.6.9), I get

> python3 -c "import motor_interface"
Segmentation fault (core dumped)

I tried in IPython (version 7.16.3 with python 3.6.9) and I get:

In [1]: import motor_interface
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-1-070d76b3d185> in <module>
----> 1 import motor_interface

ImportError: path_to_folder/motor_interface.so: undefined symbol: _Py_ZeroStruct

For the heck of it I tried in Python 2 (2.7.17) and got

python2 -c "import motor_interface"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: ./motor_interface.so: undefined symbol: _ZN3ros7console13g_initializedE

These errors, based on my search for a fix, sound like a problem with mismatched python versions; however, since I set PYBIND11_PYTHON_VERSION to 3.6.9 and then use 3.6.9, I don't think that should be the problem.

It sounds like it could be a missing library? I link against the only ones I know I use, though. What do you all think?