How to detect successful login?

I am making a automation script on python to read a dump of accounts from a .txt file and trying each of them onto the application. The script works so far but after a log in is successful the program keeps running. How could I detect if the login is successful. The application is the Minecraft Launcher if anyone finds it helpful.

If you use the Minecraft website to log in, what you could do is use beautiful soup and selenium together. Selenium is a really useful tool that allows you to run a browser in headless mode; essentially this gives you unlimited automation access to a browser of your choice. You can use selenium to enter the details into the login input fields by gathering tags for the input fields, then you can execute the function that is assigned to the submit button. After this, you can use beautiful soup to search for an HTML element that ONLY appears on successful logins. FOr instance, when you log in successfully here on MPGH it shows you a message that says "You have successfully logged in", if you searched for that element but it returned None, then you didn't log in, however more often then not, you would find that element if it was a successful login.