If ROS (melodic) needs to support python3 we may have to recompile ROS source code using python3 which is not practical. So what we can do is to run python3 programs, separately and connect using ROS bridge. (if we use custom messages (ROS msg) However, if we are not using any custom rosmsg and using only built-in rosmsg, we can do the following steps to run python3 codes in ROS (without using a ROS bridge.) Install ROS (here I install Melodic) apt install ros-melodic-desktop-full. After installing ROS, install rospkg for python3. apt install python3-pip python3-all-dev python3-rospkg. This will prompt to install python3-rospkg and to remove ROS packages (already installed). Select Yes for that prompt. This will remove ROS packages and we will have to re-install them. apt install ros-melodic-desktop-full --fix-missing. This will complete the installation part