Python - Adding/Appending Data to CSV Files

You are the man! Thank you so much! I've been struggling on a project but you've made it just that much easier for me 😃

Thank you.
One question; how about the situation that I want to add a new column using the data I have in my csv file? for example I have 2 columns in my csv file called open and close. I want to add a new column that shows (close - open)/open
I know it should be a code like follow
with open('IBM.csv', 'r')as input:
with open ('IBM.csv', 'w') as output:
writer = csv.writer(output, lineterminator='\n')
reader=csv.reader(input)
And then I need to use append. but I have no idea now to put all this together and write my final code!

How to add additional columns instead of rows

How can I do it if it is at S3 location?

Awesome. Thank you!

Thanks