Most of the time, code should be written in such a way that it is easy to understand on its own. However, if you want to include a piece of information to explain a part of your code, you can use the # sign. A line of text preceded by a # is called a comment. The machine does not run this code — it is only for humans to read. When you look back at your code later, comments may help you figure out what it was intended to do.

# this variable counts how many rows of the spreadsheet we have:
row_count = 13