def diff_jaccard(str1, str2):
    """
    Calculates the Jaccard similarity between two strings.

    :param str1: First string.
    :param str2: Second string.
    :return: float in the [0, 1] interval
    """
    assert type(str1) == list and type(str2) == list
    assert type(str1[0]) == str and type(str2[0]) == str
    a = set(str1)
    b = set(str2)
    c = a.intersection(b)
    return float(len(c)) / (len(a) + len(b) - len(c))
