python中的buggy置换

我已经为排列编写了java代码,但未能翻译成python。它们都是传递值,但我不明白为什么。输出给我 [[1, 2, 3], [1, 2, 3], [1, 2, 3enter code here]]

def permutation(nums):
    nums.sort()
    ans = []
    backTrack([], ans, nums)
    return ans

def backTrack(tempList, ans, nums):
    if len(tempList) == len(nums):
        newList = tempList[:]
        ans.append(newList)
    else:
        for i in range(len(nums)):
            if nums[i] in tempList:
                continue
            tempList.append(nums[i])
            backTrack(tempList, ans, nums)
            tempList = tempList[:-1]

ans = permutation([1, 2, 3])
print(ans)