实用字符串count函数,先比较输入的字符串那个长,要计算公共子串必定长的去计算短的

while True:

try:
    string1 = input()
    string2 = input()
    n = len(string1)
    m = len(string2)
    count = 0
    lens = 0
    flag = 0
    if m >= n:  # 看那个长
        for i in range(n, 0, -1):  # 因为计算最长的,所以循环从大到小
            for j in range((n-i + 1)): **# 依次从0开始选择 如string1字符串为abcdef,i为 6  string1[j:i+j]就是本身, 当i为5时 string1[j:i+j]abcde和bcdef 当i为四时 string1[j:i+j]为abcd bcde cdef**
                count = string2.count(string1[j:i+j])
                if count:
                    flag = 1
                    break
            if flag:
                lens = i
                break
    else:
        for i in range(m, 0, -1):
            for j in range((m-i + 1)):
                count = string1.count(string2[j:i+j])
                if count:
                    flag = 1
                    break
            if flag:
                lens = i
                break
    print(lens)
except:
    break