We will keep account.cpp unchanged with respect to the previous two recipes and only modify account.hpp:

#pragma once

#include <pybind11/pybind11.h>

class Account {
public:
  Account();
  ~Account();

  void deposit(const double amount);
  void withdraw(const double amount);
  double get_balance() const;

private:
  double balance;
};

namespace py = pybind11;

PYBIND11_MODULE(account, m) {
  py::class_<Account>(m, "Account")
      .def(py::init())
      .def("deposit", &Account::deposit)
      .def("withdraw", &Account::withdraw)
      .def("get_balance", &Account::get_balance);
}

We will follow the pybind11 documentation "Building with CMake" (https://pybind11.readthedocs.io/en/stable/compiling.html#building-with-cmake) and introduce the pybind11 CMake code using add_subdirectory. However, we will not place the pybind11 source code explicitly into our project directory, but rather demonstrate how to fetch pybind11 sources at configure time using FetchContent (https://cmake.org/cmake/help/v3.11/module/FetchContent.html).

For better code reuse in the next recipe, we will also place all sources into a subdirectory and use the following project layout:

.
├── account
│   ├── account.cpp
│   ├── account.hpp
│   ├── CMakeLists.txt
│   └── test.py
└── CMakeLists.txt