附加列表与附加列表之间的区别[:]

Question

I am trying to traverse into a string using DFS and appending it to result in the line highlighted. However if I use result.append(currlist) vs result.append(currlist[:]) , the result is totally different. The former doesn't work, why is that?

class Solution: 
       
    def dfs(self, start, s, currlist, result):
        if start >= len(s):
            result.append(currlist[:])  # <--
            return
        
        for end in range(start, len(s)):
            currlist.append(s[start:end+1])
            self.dfs(end+1, s, currlist, result)
            currlist.pop()
        
    def partition(self, s: str) -> List[List[str]]:
        result = []
        self.dfs(0, s, [], result)
        return result

Answer 1

list[:] creates a copy of the object

Example:

x = []
y = [0, 1]

x.append(y)
print(x)

y[0] = 2

print(x)

Output:

 [[0, 1]] [[2, 1]]

x = []
y = [0, 1]

x.append(y[:])
print(x)

y[0] = 2

print(x)

Output:

 [[0, 1]] [[0, 1]]