To use a custom Python build (e.g., if you built Python from source), run make with the appropriate CXX, CXXFLAGS, and LDFLAGS environment variables.

For example:

export PYTHON_HOME=/path/to/your/custom/python/installation
CXX="clang++ -mmacosx-version-min=14.6 -std=c++20" CXXFLAGS="-I${PYTHON_HOME}/include/python3.15d" LDFLAGS="-L${PYTHON_HOME}/lib -lpython3.15d" make

The demo currently requires a custom-built CPython 3.15 from https://github.com/itamaro/cpython/tree/gh-116146-create-builtin-initfunc

After building, you can run the executable from the project root:

./demo script.py