Set PYTHON_INSTALL_DIR based on Python3_SITEARCH

Python3_SIETARCH is relative, but PYTHON_INSTALL_DIR is absolute. So
strip the Python3_PREFIS from Python3_SITEARCH to form a relative path.

This is preferable to the current hardcoded path, but is also
preferable to using an absolute path, as suggested in AcademySoftwareFoundation#523.

Signed-off-by: Cary Phillips <cary@ilm.com>

Author: fundawang

src/pybind11/PyBindImath/CMakeLists.txt

@@ -127,8 +127,21 @@ if (IMATH_INSTALL)
     # Set the PYTHON_INSTALL_DIR but only if it's not already set,
     # which allows an externally-set value to take effect.
     #
-  
-    set(PYTHON_INSTALL_DIR "lib/python${Python3_VERSION_MAJOR}.${Python3_VERSION_MINOR}/site-packages")
+    # PYTHON_INSTALL_DIR should be a relative path underneath the 
+    # INSTALL_DIR. Set it to Python3_SITEARCH, relative to the python
+    # system installation.
+    #
+    
+    if (NOT Python3_PREFIX)
+      # if Python3_PREFIX is not set, use the location of the python executable
+      get_filename_component(Python3_PREFIX "${Python3_EXECUTABLE}" DIRECTORY)
+      get_filename_component(Python3_PREFIX "${Python3_PREFIX}" DIRECTORY)
+    endif()
+
+    file(RELATIVE_PATH PYTHON_INSTALL_DIR
+      "${Python3_PREFIX}"
+      "${Python3_SITEARCH}")
+
     message(STATUS "installing ${PYBINDIMATH_MODULE_NAME} to ${PYTHON_INSTALL_DIR}")
 
   else()

src/python/PyImath/CMakeLists.txt

@@ -212,8 +212,21 @@ if (IMATH_INSTALL)
     # Set the PYTHON_INSTALL_DIR but only if it's not already set,
     # which allows an externally-set value to take effect.
     #
-  
-    set(PYTHON_INSTALL_DIR "lib/python${Python3_VERSION_MAJOR}.${Python3_VERSION_MINOR}/site-packages")
+    # PYTHON_INSTALL_DIR should be a relative path underneath the 
+    # INSTALL_DIR. Set it to Python3_SITEARCH, relative to the python
+    # system installation.
+    #
+    
+    if (NOT Python3_PREFIX)
+      # if Python3_PREFIX is not set, use the location of the python executable
+      get_filename_component(Python3_PREFIX "${Python3_EXECUTABLE}" DIRECTORY)
+      get_filename_component(Python3_PREFIX "${Python3_PREFIX}" DIRECTORY)
+    endif()
+
+    file(RELATIVE_PATH PYTHON_INSTALL_DIR
+      "${Python3_PREFIX}"
+      "${Python3_SITEARCH}")
+
     message(STATUS "installing ${PYIMATH_MODULE_NAME} module to ${PYTHON_INSTALL_DIR}")
 
   else()

src/python/PyImathNumpy/CMakeLists.txt

@@ -50,14 +50,27 @@ target_link_libraries(${PYIMATHNUMPY_MODULE}
 
 if (IMATH_INSTALL)
 
-  #
-  # Set the PYTHON_INSTALL_DIR but only if it's not already set,
-  # which allows an externally-set value to take effect.
-  #
-  
   if (NOT DEFINED PYTHON_INSTALL_DIR)
 
-    set(PYTHON_INSTALL_DIR "lib/python${Python3_VERSION_MAJOR}.${Python3_VERSION_MINOR}/site-packages")
+    #
+    # Set the PYTHON_INSTALL_DIR but only if it's not already set,
+    # which allows an externally-set value to take effect.
+    #
+    # PYTHON_INSTALL_DIR should be a relative path underneath the 
+    # INSTALL_DIR. Set it to Python3_SITEARCH, relative to the python
+    # system installation.
+    #
+    
+    if (NOT Python3_PREFIX)
+      # if Python3_PREFIX is not set, use the location of the python executable
+      get_filename_component(Python3_PREFIX "${Python3_EXECUTABLE}" DIRECTORY)
+      get_filename_component(Python3_PREFIX "${Python3_PREFIX}" DIRECTORY)
+    endif()
+
+    file(RELATIVE_PATH PYTHON_INSTALL_DIR
+      "${Python3_PREFIX}"
+      "${Python3_SITEARCH}")
+
     message(STATUS "installing ${PYIMATHNUMPY_MODULE} module to ${PYTHON_INSTALL_DIR}")
 
   else()