According to the Python developers' policy of changing PY_VERSION after a patch version freeze (commits like "Python 3.X.y" and "Post 3.X.y"), now it is not possible to build a CMake Python after the "Post" stage, because the MY_RELEASE_SERIAL variable in python_extract_version_info() becomes "+", and the following statement fails:

math(EXPR _field3 "${_patch} * 1000 + ${_level_number} * 10 + ${_serial}")

Maybe add extra fallback here?

    if("${MY_RELEASE_SERIAL}" STREQUAL "")
        set(MY_RELEASE_SERIAL 0)
    endif()