The C++ program defines a set_the_answer lambda that can receive the new value and passes it as local to the input-number.py script.
The Python script creates an (PyQt) application that is showing an input dialog. If the Ok button is pressed, the set_the_answer() function passes the value to the C++ code.
One big warning: the set_the_answer() function is not visisble inside of get_the_value(): pybind11 is passing the set_the_answer() as a local to the eval (exec, in reality) Python context: we need to explicitely pass the outer local context to the get_the_value(), and visible inside of it.
(I've been told that this is becaue Python executes the code as if it was in a class environment...)
$ mkdir build
$ cd build
$ cmake ..
$ make
$ ./scripting