使用Stack Pop回溯Python

I'm using backtracking to get permutations of non-duplicates nums list. E.g nums = [1, 2, 3], the output should be '[[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]. I'm stuck on pop elements out from recursively stack. Anyone can help me what's the problem of my code. Thanks.I'm using backtracking to get permutations of n