def get_edit_distance(s1, s2):
    """Calculate the Levenshtein distance between two normalised strings
    Adopted from example in https://stackoverflow.com/questions/2460177/edit-distance-in-python
    See https://en.wikipedia.org/wiki/Edit_distance
    @param s1: the first string to compare
    @param s2: the second string to compare
    @returns: an integer giving the edit distance
    """
    if len(s1) > len(s2):
        s1, s2 = s2, s1
    distances = range(len(s1) + 1)
    for i2, c2 in enumerate(s2):
        distances_ = [i2 + 1]
        for i1, c1 in enumerate(s1):
            if c1 == c2:
                distances_.append(distances[i1])
            else:
                distances_.append(1 + min((distances[i1], distances[i1 + 1],
                    distances_[-1])))
        distances = distances_
    return distances[-1]
