Only in patched: build
diff -ura orig/ros_workspace-release-release-ardent-ros_workspace-0.4.0-0/CMakeLists.txt patched/ros_workspace-release-release-ardent-ros_workspace-0.4.0-0/CMakeLists.txt
--- orig/ros_workspace-release-release-ardent-ros_workspace-0.4.0-0/CMakeLists.txt	2017-12-09 05:27:00.000000000 +0100
+++ patched/ros_workspace-release-release-ardent-ros_workspace-0.4.0-0/CMakeLists.txt	2017-12-20 22:15:29.467345783 +0100
@@ -3,7 +3,7 @@
 
 find_package(ament_cmake_core REQUIRED)
 
-set(PYTHON_INSTALL_DIR "lib/python3.5/site-packages")
+set(PYTHON_INSTALL_DIR "lib/python3.6/site-packages")
 set(ament_cmake_package_templates_ENVIRONMENT_HOOK_PYTHONPATH "${CMAKE_INSTALL_PREFIX}/${PYTHON_INSTALL_DIR}/ament_package/template/environment_hook/pythonpath.sh.in")
 ament_environment_hooks("${ament_cmake_package_templates_ENVIRONMENT_HOOK_PYTHONPATH}")