Interoperability between C / C++ and other Python binding libraries?

Haven’t yet hit a need for this, but wanted to ask anywho:

We use pybind11 in Drake, and it’d be nice if we had the ability to get interop between rclpy and rclcpp within our own binding layer.

For some external examples, people have done this with packages like OpenCV, VTK, etc.: https://github.com/virtuald/pybind11_opencv_numpy https://github.com/EricCousineau-TRI/repro/tree/b9e02d6d5a71f6315b80759ba1628b4bb383c0b8/python/vtk_pybind (my stuff, but points to the motivating examples / questions)

Granted, VTK has a rich object model which makes it relatively easy to do the interop. OpenCV is implemented in pure C++, hence the ease of use with pybind C++.

My technical guesses:

• Interop between rcl C and rclpy should be more or less straightforward, would just require experimental / unstable APIs to be exposed (or copied + pasted) from the bindings here.
• Interop between rclpp and rclpy would be much more challenging, as the C++ API (rightly so) encapsulates the underlying C structs.
  • This may be achievable by creating C++ Python bindings that have parity with the rclpy API. It would require more overhead in terms of maintenance, compilation, size, etc; however, the unittests here look very extensive, so it should be relatively easy to confirm useful parity 😃

As an alternative, we can do what we do for LCM, where we introduce our own wrapper interface… but this has given me personally many sad faces for API interop + decoupling (heavy frameworks…), utilities, generalization, etc.: https://drake.mit.edu/pydrake/pydrake.lcm.html https://drake.mit.edu/doxygen_cxx/classdrake_1_1lcm_1_1_drake_lcm.html (doc produced at or around drake@361223416)

[sloretz]

I am currently encountering issues in doing so, I have a class whose constructor accepts a shared pointer reference to a node instance. I wish to create this node using rclpy and pass it to MoveIt as follows.

It looks like your API expects an rclcpp::Node::SharedPtr &, but your example is passing it the Python class rclpy.node.Node. Those are different types.

I was hoping that users would be able to leverage the rclpy library to create nodes which could be passed to MoveIt through the Python API.

Note that rclpy doesn’t use rclcpp, so it has no conversions to rclcpp types. It does have a way to get the rcl type rcl_node_t. If moveit has APIs using rcl types, then that’s your starting point. Otherwise you’d need rclcpp to offer a way to create an rclcpp::Node instance from a borrowed rcl_node_t *, which I don’t think exists.

[mjcarroll]

There was a proof-of-concept developed, but it’s probably quite stale at this point: https://github.com/ros2/rclpy/tree/proof_of_concept_pybind11

@sloretz (the original author of this PoC) would probably be the best person to weigh in here.