Question

I want to compare the values in one list to the values in a second list and return all those that are in the first list but not in the second i.e.

list1 = ['one','two','three','four','five']
list2 = ['one','two','four']

would return ‘three’ and ‘five’.

I have only a little experience with python, so this may turn out to be a ridiculous and stupid way to attempt to solve it, but this what I have done so far:

def unusedCategories(self):
    unused = []
    for category in self.catList:
        if category != used in self.usedList:
            unused.append(category)
    return unused

However this throws an error ‘iteration over non-sequence’, which I gather to mean that one or both ‘lists’ aren’t actually lists (the raw output for both is in the same format as my first example)

Answer 1

Use sets to get the difference between the lists:

>>> list1 = ['one','two','three','four','five']
>>> list2 = ['one','two','four']
>>> set(list1) - set(list2)
set(['five', 'three'])