How can I calculate the Jaccard Similarity of two lists containing strings in Python?

I ended up writing my own solution after all:

def jaccard_similarity(list1, list2):
    intersection = len(list(set(list1).intersection(list2)))
    union = (len(list1) + len(list2)) - intersection
    return float(intersection) / union

For Python 3:

def jaccard_similarity(list1, list2):
    s1 = set(list1)
    s2 = set(list2)
    return float(len(s1.intersection(s2)) / len(s1.union(s2)))
list1 = ['dog', 'cat', 'cat', 'rat']
list2 = ['dog', 'cat', 'mouse']
jaccard_similarity(list1, list2)
>>> 0.5

For Python2 use return len(s1.intersection(s2)) / float(len(s1.union(s2)))

@aventinus I don't have enough reputation to add a comment to your answer, but just to make things clearer, your solution measures the jaccard_similarity but the function is misnamed as jaccard_distance, which is actually 1 - jaccard_similarity