I have seen similar questions here, but I didn't get my answer. Maybe it's because I am new to all this and just don't understand. I want my app to work mostly as an indicator. And if user would start it again it would check if it is already running, if it is then give all the input data to that process and quit. So first I need to check if it is running. I saw the answer where you can make a file witch when the program starts and then check if it exists... But what if someone would delete it? Can't I just ask the OS if there is process named "myApp" or something? The next thing I don't really get is how to communicate with the process. How do I give it the input data and what is it going to do with it? Does it work just like starting a new app, through the main() method? I am trying to create this using Quickly. So it would be nice if you can give me some python examples or link to something like that.