its Python_ROOT_DIR not PYTHON_ROOT

cmake_support/FindOPENSTRUCTURE.cmake

@@ -27,7 +27,7 @@ macro(find_OPENSTRUCTURE OST_ROOT HEADER_NAMES PYMOD_NAME)
     set(FOUND_LIB FOUND_LIB-NOTFOUND)
     find_library(FOUND_LIB 
       NAMES ost_${LIB}
-      HINTS "${Python_ROOT}"
+      HINTS "${Python_ROOT_DIR}"
       PATH ${OST_ROOT}
       PATH_SUFFIXES lib lib64
       NO_SYSTEM_ENVIRONMENT_PATH NO_DEFAULT_PATH

doc/buildsystem.rst

@@ -65,7 +65,7 @@ headers would be located in ``OST_ROOT/include/ost``).
 Similarly, one can specify folders for |boost|, |python| and |eigen3| 
 if multiple versions exist and/or they are not installed in a default location.
 These are set with the ``BOOST_ROOT`` (make sure that's the same as for |ost_s|), 
-``Python_ROOT`` and ``EIGEN3_INCLUDE_DIR``.
+``Python_ROOT_DIR`` and ``EIGEN3_INCLUDE_DIR``.
 
 Here is a list of more options used within |project|: