Question

I know this question has been discussed before, and I know this is such a novice and easy question, but for some reason I can’t wrap my head around the code that would be needed to do this. Here is a practical example that I need this for:

Lets say I contain a tumblr account, and I follow 5 people, of which 3 follow me back.

iFollow = [Tom, Richard, Bob, Samantha, Kat]
followsMe = [Samantha, Kat, Bob]

Now, I want to unfollow the people that I follow, however don’t follow me back.
So in this example I would want to unfollow Tom and Richard, because even though I follow them, they don’t follow me. I would like to create a list:

unfollowThese = [Tom, Richard]

I can’t for the life of me figure out how to do this. I know there is intersect, find the common elements, that would output “Bob”, it seems like I want the opposite, I want elements that are common in both lists removed from the new list that I want to make.

I.E. I want elements common in iFollow and followsMe to be removed from unfollowThese, as I don’t want to unfollow my followers.

Thanks.

p.s. if you can think of a better title, please change it, I couldn’t think of anything to call it..

Answer 1

Using list comprehensions if order matters:

unfollowThese = [ person for person in iFollow if person not in followsMe ]

Using sets if the order of items does not matter:

import sets
s1 = sets.Set(iFollow)
unfollowThese = s1.difference(followsMe)