Python生成排列时添加到列表的方式不正确

在本例中,为什么会生成正确的结果:

nxt = path + [nums[i]]

但不是:

nxt = path ; nxt += [nums[i]]

nxt = path ; nxt.append(nums[i])

def permute(nums):
    def dfs(nums, path):
      if not nums: # empty, done with path
          all_perms.append(path)
          return

      for i in range(len(nums)):
        nxt = path + [nums[i]]
        # nxt = path ; nxt += [nums[i]]
        # nxt = path ; nxt.append(nums[i])
        print(nxt)
        dfs(nums[:i] + nums[i+1:], nxt)

    all_perms = []
    dfs(nums, [])
    return all_perms