`emplaceAndPop(): incompatible function arguments` with Python 3.10 and `PyEval_InitThreads()` warning

[reinethernal]

I am encountering an issue when trying to build and use OpenPose's Python bindings with Python 3.10. The pyopenpose module compiles, but when trying to run a Python script that uses openpose_wrapper.emplaceAndPop(), it fails with an incompatible function arguments error. Additionally, during compilation, a PyEval_InitThreads() deprecation warning is observed, originating from OpenPose's bundled pybind11.
Problem:
When calling openpose_wrapper.emplaceAndPop() from Python, I get the following error:

TypeError: emplaceAndPop(): incompatible function arguments. The following argument types are supported:

1. emplaceAndPop(self: openpose.pyopenpose.WrapperPython, datum_vector: List[openpose.pyopenpose.Datum]) -> None
   Invoked with: <openpose.pyopenpose.WrapperPython object at 0x...>, None

(Note: The None in "Invoked with: ... None" is likely a symptom, not the root cause, as the object is initialized.)

During make compilation, I also see this warning, pointing to an outdated pybind11 being used:

In file included from /root/tryroom/openpose/3rdparty/pybind11/include/pybind11/cast.h:16,
from /root/tryroom/openpose/3rdparty/pybind11/include/pybind11/attr.h:13,
from /root/tryroom/openpose/3rdparty/pybind11/include/pybind11/pybind11.h:44,
from /root/tryroom/openpose/python/openpose/openpose_python.cpp:8:
/root/tryroom/openpose/3rdparty/pybind11/include/pybind11/detail/internals.h: In function ‘pybind11::detail::internals& pybind11::detail::get_internals()’:
/root/tryroom/openpose/3rdparty/pybind11/include/pybind11/detail/internals.h:200:27: warning: ‘void PyEval_InitThreads()’ is deprecated [-Wdeprecated-declarations]
200 | PyEval_InitThreads();
| ~~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/python3.10/Python.h:130,
from /root/tryroom/openpose/3rdparty/pybind11/include/pybind11/detail/common.h:112,
...
/usr/include/python3.10/ceval.h:122:37: note: declared here
122 | Py_DEPRECATED(3.9) PyAPI_FUNC(void) PyEval_InitThreads(void);

Environment:

• OpenPose Version: (Specify the version you are using, e.g., the commit hash if cloned from git, or the release version if downloaded)
• Operating System: Ubuntu 22.04 LTS
• Python Version: 3.10
• CUDA Version: 12.6
• cuDNN Version: 9.7.1
• GCC Version: 11.4.0
• OpenCV Version: 4.5.4 (as reported by CMake)

Steps Taken (and their outcomes):

1. Clean build of OpenPose.
2. Explicitly set Python paths during CMake configuration:

   cmake .. \
       -DBUILD_PYTHON=ON \
       -DPYTHON_EXECUTABLE=/root/tryroom/venv/bin/python3 \
       -DPYTHON_INCLUDE_DIR=/root/tryroom/venv/include/python3.10 \
       -DPYTHON_LIBRARY=/root/tryroom/venv/lib/libpython3.10.so \
       -DUSE_CUDA=ON \
       -DBUILD_CAFFE=ON \
       -DOpenCV_DIR=/usr/local/opencv/build \
       -DCUDNN_INCLUDE_DIR=/usr/local/cuda/include \
       -DCUDNN_LIBRARY=/usr/local/cuda/lib64

   Result: CMake proceeds, but warns "Manually-specified variables were not used by the project: ... PYTHON_EXECUTABLE, PYTHON_INCLUDE_DIR, PYTHON_LIBRARY".
3. Attempted to force system pybind11 using USE_SYSTEM_PYBIND11=ON flag:
   Result: This flag was also ignored by CMake.
4. Modified openpose/python/openpose/CMakeLists.txt to add find_package(pybind11 CONFIG REQUIRED) before pybind11_add_module.
   Result: CMake did not report finding pybind11 explicitly, and Python-related variables were still warned as unused. The PyEval_InitThreads() warning persists during make.

Observation:
The compilation warning explicitly points to openpose/3rdparty/pybind11/, indicating that OpenPose is using its bundled, likely outdated, pybind11 which is incompatible with Python 3.10's API (specifically PyEval_InitThreads deprecation). The CMake configuration seems to override attempts to use an external pybind11 or explicitly specified Python paths.

Expected behavior:
OpenPose Python bindings should compile and run correctly with Python 3.10, utilizing a compatible pybind11 version.

Any guidance or known workarounds for this compatibility issue would be greatly appreciated.