python: update install paths

- don't require "OPENCV_PYTHON{2,3}_INSTALL_PATH" if OPENCV_SKIP_PYTHON_LOADER=ON
- avoid unnecessary relative paths in generated config-X.Y.py

CMakeLists.txt

@@ -1494,7 +1494,7 @@ if(BUILD_opencv_python2)
     status("    Libraries:"   HAVE_opencv_python2  THEN  "${PYTHON2_LIBRARIES}"                                      ELSE NO)
   endif()
   status("    numpy:"         PYTHON2_NUMPY_INCLUDE_DIRS THEN "${PYTHON2_NUMPY_INCLUDE_DIRS} (ver ${PYTHON2_NUMPY_VERSION})" ELSE "NO (Python wrappers can not be generated)")
-  status("    packages path:" PYTHON2_EXECUTABLE         THEN "${PYTHON2_PACKAGES_PATH}"                                    ELSE "-")
+  status("    install path:"  HAVE_opencv_python2  THEN "${__INSTALL_PATH_PYTHON2}"                            ELSE "-")
 endif()
 
 if(BUILD_opencv_python3)
@@ -1507,7 +1507,7 @@ if(BUILD_opencv_python3)
     status("    Libraries:"   HAVE_opencv_python3  THEN  "${PYTHON3_LIBRARIES}"                                      ELSE NO)
   endif()
   status("    numpy:"         PYTHON3_NUMPY_INCLUDE_DIRS THEN "${PYTHON3_NUMPY_INCLUDE_DIRS} (ver ${PYTHON3_NUMPY_VERSION})" ELSE "NO (Python3 wrappers can not be generated)")
-  status("    packages path:" PYTHON3_EXECUTABLE         THEN "${PYTHON3_PACKAGES_PATH}"                                    ELSE "-")
+  status("    install path:"  HAVE_opencv_python3  THEN "${__INSTALL_PATH_PYTHON3}"                            ELSE "-")
 endif()
 
 status("")

modules/python/common.cmake

@@ -122,6 +122,8 @@ endif()
 
 if(NOT " ${PYTHON}" STREQUAL " PYTHON" AND DEFINED OPENCV_${PYTHON}_INSTALL_PATH)
   set(__python_binary_install_path "${OPENCV_${PYTHON}_INSTALL_PATH}")
+elseif(OPENCV_SKIP_PYTHON_LOADER AND DEFINED ${PYTHON}_PACKAGES_PATH)
+  set(__python_binary_install_path "${${PYTHON}_PACKAGES_PATH}")
 else()
   ocv_assert(DEFINED OPENCV_PYTHON_INSTALL_PATH)
   set(__python_binary_install_path "${OPENCV_PYTHON_INSTALL_PATH}/${__python_loader_subdir}python-${${PYTHON}_VERSION_MAJOR}.${${PYTHON}_VERSION_MINOR}")
@@ -134,6 +136,8 @@ install(TARGETS ${the_module}
         ${PYTHON_INSTALL_ARCHIVE}
         )
 
+set(__INSTALL_PATH_${PYTHON} "${__python_binary_install_path}" CACHE INTERNAL "")  # CMake status
+
 if(NOT OPENCV_SKIP_PYTHON_LOADER)
   ocv_assert(DEFINED OPENCV_PYTHON_INSTALL_PATH)
   if(OpenCV_FOUND)
@@ -143,12 +147,11 @@ if(NOT OPENCV_SKIP_PYTHON_LOADER)
   endif()
 
   set(__python_loader_install_tmp_path "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/install/python_loader/")
+  set(OpenCV_PYTHON_LOADER_FULL_INSTALL_PATH "${CMAKE_INSTALL_PREFIX}/${OPENCV_PYTHON_INSTALL_PATH}/cv2")
   if(IS_ABSOLUTE "${OPENCV_PYTHON_INSTALL_PATH}")
-    set(OpenCV_PYTHON_INSTALL_PATH_RELATIVE_CONFIGCMAKE "${CMAKE_INSTALL_PREFIX}/")
-    set(CMAKE_PYTHON_EXTENSION_INSTALL_PATH_BASE "'${CMAKE_INSTALL_PREFIX}'")
+    set(CMAKE_PYTHON_EXTENSION_INSTALL_PATH_BASE "'${OPENCV_PYTHON_INSTALL_PATH}/cv2'")
   else()
-    file(RELATIVE_PATH OpenCV_PYTHON_INSTALL_PATH_RELATIVE_CONFIGCMAKE "${CMAKE_INSTALL_PREFIX}/${OPENCV_PYTHON_INSTALL_PATH}/cv2" ${CMAKE_INSTALL_PREFIX})
-    set(CMAKE_PYTHON_EXTENSION_INSTALL_PATH_BASE "os.path.join(LOADER_DIR, '${OpenCV_PYTHON_INSTALL_PATH_RELATIVE_CONFIGCMAKE}')")
+    set(CMAKE_PYTHON_EXTENSION_INSTALL_PATH_BASE "LOADER_DIR")
   endif()
 
   if(DEFINED ${PYTHON}_VERSION_MINOR)
@@ -167,7 +170,8 @@ if(NOT OPENCV_SKIP_PYTHON_LOADER)
   if(IS_ABSOLUTE __python_binary_install_path)
     set(CMAKE_PYTHON_EXTENSION_PATH "'${__python_binary_install_path}'")
   else()
-    set(CMAKE_PYTHON_EXTENSION_PATH "os.path.join(${CMAKE_PYTHON_EXTENSION_INSTALL_PATH_BASE}, '${__python_binary_install_path}')")
+    file(RELATIVE_PATH OpenCV_PYTHON_BINARY_RELATIVE_INSTALL_PATH "${OpenCV_PYTHON_LOADER_FULL_INSTALL_PATH}" "${CMAKE_INSTALL_PREFIX}/${__python_binary_install_path}")
+    set(CMAKE_PYTHON_EXTENSION_PATH "os.path.join(${CMAKE_PYTHON_EXTENSION_INSTALL_PATH_BASE}, '${OpenCV_PYTHON_BINARY_RELATIVE_INSTALL_PATH}')")
   endif()
   configure_file("${PYTHON_SOURCE_DIR}/package/template/config-x.y.py.in" "${__python_loader_install_tmp_path}/cv2/${__target_config}" @ONLY)
   install(FILES "${__python_loader_install_tmp_path}/cv2/${__target_config}" DESTINATION "${OPENCV_PYTHON_INSTALL_PATH}/cv2/" COMPONENT python)