How to bind C++ non-arguments function to Python constant attributes/variables ?

[linrongbin16]

Hi, I'm trying to bind C++ class static non-arguments method to python class static constant field.

Here's my sample code config.cpp:

namespace py = pybind11;

struct Env {
  static std::string env() {
    return std::getenv("MY_ENV");
  }
};

PYBIND11_MODULE(config, m) {
  m.doc() = "my config module written in C++";
  py::class_<Env>(m, "Env")
    .def_property_readonly_static("ENV", &Env::env);
}

The config module compiles successfully, but when I use it in python3 console, here's the exception it raise:

>>> import config
>>> Env.ENV
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: (): incompatible function arguments. The following argument types are supported:
    1. () -> str

Invoked with: <class 'config.Env'>

How should I fix this ?

[linrongbin16]

Or is there a way to bind C++ function to python module constant attributes/variables ?

[linrongbin16]

I found answer here: https://pybind11.readthedocs.io/en/stable/advanced/classes.html#static-properties. use def_property_readonly_static with lambda could bind C++ class static non-arguments method to Python class static constant attributes/variables.

But I still have no idea about how to bind C++ non-arguments function to Python constant attributes/variables.