Pybind11/Nanobind: How to return class object and use methods from Python. How can I cast the C++ object to something whose methods I can use in Py

Question

I'm not sure why I can't find any good discussion of this, I have been searching since yesterday.

How do you return a class object from C++ binding and use its methods in Python i.e.:

class A {
    ...
    void foo() {
        py::print("Hello world");
    }
}

class B {
    ...
    A bar() {
        a = A();
        // What do I return here if I want to return a and use it in Python
        // return a
    }
}

I want to then bind B and use it in Python

b_object = B()
a = b_object.bar()
a.foo()

How do I do this in Pybind, Nanobind or Boost Python (if the syntax for the latter is similar).

I can't use lambdas when creating the B binding. The use case is actually more complex than what I've shown here.