directory structure for a project that mixes C++ and Python

Question

Say you want want to create a programming project that mixes C++ and Python. The Foo C++ project structure uses CMake, and a Python module is created by using Swig. The tree structure would look something like this:

├── CMakeLists.txt
├── FooConfig.cmake.in
├── FooConfigVersion.cmake.in
├── Makefile
├── README
├── foo
│   ├── CMakeLists.txt
│   ├── config.hpp.in
│   ├── foo.cpp
│   └── foo.hpp
└── swig
    └── foo.i

Now you would like to make use of the Foo project within a Python project, say Bar:

├── AUTHORS.rst
├── CONTRIBUTING.rst
├── HISTORY.rst
├── LICENSE
├── MANIFEST.in
├── Makefile
├── README.rst
├── docs
│   ├── Makefile
│   ├── authors.rst
│   ├── conf.py
│   ├── contributing.rst
│   ├── history.rst
│   ├── index.rst
│   ├── installation.rst
│   ├── make.bat
│   ├── readme.rst
│   └── usage.rst
├── bar
│   ├── __init__.py
│   └── bar.py
├── requirements.txt
├── setup.cfg
├── setup.py
├── tests
│   ├── __init__.py
│   └── test_bar.py
└── tox.ini

This structure was crated by using cookiecutter's pypackage template. A BoilerplatePP template is also available to generate a CMake C++ project using cookiecutter (no Swig part). So now that I have the structure of both projects, and considering that the development will take place mainly in Python and the the project will be run in different systems, I need to address the following questions:

1. What's the best way to mix them? Should I collapse both root directories? Should I have the Foo C++ project as a directory of the Bar project or the other way around? I may be inclined to put the entire C++ structure shown above in a folder at the root level of the Python project, but I would like to know a priori any pitfalls as the CMake system is quite powerful and it may be convenient to do it the other way around.
2. In case I decide to put the Foo project as a directory within Bar, is the Python setuptools package as powerful as the CMake build system? I ask this because when I take a look at the Bar project, at the top level it seems there's only a bunch of scripts, but I don't know if this is the equivalent to CMake as I'm new to Python.
3. The Bar project outlined above has a single bar directory, but I assume that whenever this project expands, instead of having many other directories at the root level, other directories containing Python code will be placed within bar. Is this correct (in the Pythonic sense)?
4. I assume that a single egg will be produced from the entire project, so that it can be installed and run in many different python systems. Is the integration of the module created by the Foo project easy? I assume that this module will be created in a different directory than bar.
5. In order for the Python code within the bar directory, the module created by Swig has to be available, so I guess the most straightforward way to do this is to modify the environmental variable PYTHONPATH using the CMake system. Is this fine or is there a better way?

Answer 1

If the C++ application has no use outside the Python package that will contain it:

You can pretty safely place the C++ code within the python package that owns it. Have the "foo" directory within the "bar" directory within your example. This will make packaging the final Python module a bit easier.

If the C++ application is reusable:

I would definitely try to think of things in terms of "packages", where independent parts are self-contained. All independent parts live on the same level. If one part depends on another, you import from its corresponding "package" from the same level. This is how dependencies typically work.

I would NOT include one within the other, because one does not strictly belong to the other. What if you started a third project that needed "foo", but did not need "bar"?

I would place both "foo" and "bar" packages into the same "project" directory (and I would probably give each package it's own code repository so each package can be easily maintained and installed).