I was trying to set PATH in etc/environment file, but after adding the desired path the $PATH is showing an error in terminal:

bash: /usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games: No such file or directory

Here's the content of environment file:

PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/monty/google_appengine"

I was trying to add the path to the folder google_appengine to the PATH as mentioned in this Answer, but it doesn't seem to work.