How to use matplotlib to draw to an existing Axes object at C++ side?

[UUNagato]

In my project, I want to call matplotlib to draw (mainly add patches) to an existing Axes object (created from python side) at C++ side. I am wondering how to do that with pybind11?

In other words, I create an Axes object in python. This Axes object is later used as a parameter to a C++ function. And the C++ function draws something (mainly add patches) to this Axes.

I don't know how to define a C++ function that takes an Axes object as the parameter and calls matplotlib to draw to it.

Thank you for the help.

[EricCousineau-TRI]

Have you had a chance to review the docs about accessing Python object via C++ API?
https://pybind11.readthedocs.io/en/stable/advanced/pycpp/object.html

[UUNagato]

@EricCousineau-TRI Thank you. I have solved my problem. I once believed using py::module_::import and other similar functions requires an embedded intepreter but I was wrong. May I ask another question? How can I check if a py::object parameter is a matplotlib Axes object?

[EricCousineau-TRI]

Glad it helped.

To check, you can either use py::isinstance(obj, type) (docs), or you can use py::module_::import("builtins").attr("isinstance") directly.