我不知道“最长共同的[[chain？substring？]]”与“ percent
Difference”有什么关系，尤其是在评论中看到您期望两个字符串中的一个字符相差很小时，％差异很小。中间（因此它们最长的公共子字符串大约是字符串长度的一半）。

忽略“最长共同点”的陌生性，并将“百分比差异”定义为字符串之间的编辑距离除以最大长度（当然是100倍；-），那么：

def levenshtein_distance(first, second):
    """Find the Levenshtein distance between two strings."""
    if len(first) > len(second):
        first, second = second, first
    if len(second) == 0:
        return len(first)
    first_length = len(first) + 1
    second_length = len(second) + 1
    distance_matrix = [[0] * second_length for x in range(first_length)]
    for i in range(first_length):
       distance_matrix[i][0] = i
    for j in range(second_length):
       distance_matrix[0][j]=j
    for i in xrange(1, first_length):
        for j in range(1, second_length):
            deletion = distance_matrix[i-1][j] + 1
            insertion = distance_matrix[i][j-1] + 1
            substitution = distance_matrix[i-1][j-1]
            if first[i-1] != second[j-1]:
                substitution += 1
            distance_matrix[i][j] = min(insertion, deletion, substitution)
    return distance_matrix[first_length-1][second_length-1]

def percent_diff(first, second):
    return 100*levenshtein_distance(a, b) / float(max(len(a), len(b)))

a = "the quick brown fox"
b = "the quick vrown fox"
print '%.2f' % percent_diff(a, b)

Levenshtein函数来自Stavros的博客。在这种情况下，结果将是5.26（差异百分比）。