When you create a set from wordList
it stores the string '"the'
as the only element,
>>> set(wordList)
set(['"the'])
So using set difference will return the same set,
>>> set(wordList) - set(string.punctuation)
set(['"the'])
If you want to just remove punctuation you probably want something like,
>>> [word.translate(None, string.punctuation) for word in wordList]
['the']
Here I'm using the translate
method of strings, only passing in a second argument specifying which characters to remove.
You can then perform the lemmatization on the new list.