Python 2.7 w/ selenium help with waiting for x

I have a python script that reads through a text file and deletes the first line after I click a button using selenium. Sometimes the page loads with a slight error, refreshing causes selenium to continue then deletes the line at the top of the file. I need either of the following: 1. selenium waits for the url to change before continuing 2. selenium waits for a specific button to be clicked before continuing, making a page refresh not continue the script 3. selenium waits until specific text is present on the page before continuing I believe either of those would work for what I need.