为什么我的2-d dp表不能正确更新？

Question

我正在做leetcode 5，我在下面写了解决方案。

class Solution:
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        res = (0,None)
        dp = [[0]* len(s)]*len(s)   # initialize dp table as all substring not palindrome
        # print(dp)
        # find odd palindrome
        for i in range(len(s)):
            # print('a')
            print(dp[i][i])
            dp[i][i]= 1 

            print(dp)
            if 1>res[0]:           # every element is palindrome
                res = (1,s[0])        # if this loop run, we know not empty and res at least 1
            iter = 0
            while i-iter >= 1 and i+iter <= len(s)-1 -1:
                if dp[i-iter][i+iter] == 1 and s[i-iter-1] == s[i+iter+1]:
                    dp[i-iter-1][i+iter+1] = 1
                    iter += 1
                else:
                    if 2*iter+1 > res[0]:
                        # print(i-iter,i+iter)
                        res = (2*iter+1, s[i-iter:i+iter+1])

                    break

        # find odd palindrome

        for start in range(len(s)-1):
            if s[start] == s[start+1]:
                dp[start][start+1] = 1
                if 2>res[0]:

                    res = (2,s[start:start+1 +1])
            iter = 0
            while start-iter >= 1 and (start+1)+iter <= (len(s)-1) -1:
                if dp[start-iter][(start+1)+iter] == 1 and s[start-iter-1] == s[(start+1)+iter+1]:
                    dp[start-iter-1][(start+1)+iter+1] =1
                    iter += 1
                else:
                    if 2*iter+2 > res[0]:

                        res = (2*iter+2,s[start-iter : (start+1)+iter +1])

                    break
                    # res = max(res, 2*iter+2)

        # print(dp)
        return res

当我打印dp时显示

0
[[1, 0, 0], [1, 0, 0], [1, 0, 0]]
0
[[1, 1, 0], [1, 1, 0], [1, 1, 0]]
0
[[1, 1, 1], [1, 1, 1], [1, 1, 1]]
(1, 'a')

当我只尝试更新dp时，为什么dp[i][i]会一次更新所有行？