smvsuccess

I'm trying to build a script that can scrape data from a webpage andsave it in a csv file. The bot will have to visit around 5000 links, and each time it visits one, it will have to create a new row to an existing csv with new information. The bot will run multiple times, so how can i make sure it adds to the rows below and not override previous rows? The csv i'm building will have around 5000 rows and 4-5 columns each... Thank you!