From 75c8fb12e48058966fff59795d0d11020604ca41 Mon Sep 17 00:00:00 2001
From: Julian Oes <julian@oes.ch>
Date: Wed, 15 Jan 2020 15:03:18 +0100
Subject: [PATCH] cmake: add custom error messsage about Python 3

This should be helpful as developers need to migrate to Python 3.
---
 CMakeLists.txt | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6a9fba14e6..cd2df2db54 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -267,7 +267,13 @@ endif()
 # If using catkin, Python 2 is found since it points
 # to the Python libs installed with the ROS distro
 if (NOT CATKIN_DEVEL_PREFIX)
-	find_package(PythonInterp 3 REQUIRED)
+	find_package(PythonInterp 3)
+	# We have a custom error message to tell users how to install python3.
+	if (NOT PYTHONINTERP_FOUND)
+		message(FATAL_ERROR "Python 3 not found. Please install Python 3:\n"
+			"    Ubuntu: sudo apt install python3 python3-devel python3-pip\n"
+			"    macOS: brew install python")
+	endif()
 else()
 	find_package(PythonInterp REQUIRED)
 endif()