Sword finger offer II 080 Combinatorial backtracking with k elements

The finger of the sword Offer II 080. contain k A combination of elements

class Solution:
    def combine(self, n: int, k: int) -> List[List[int]]:
        temp_ans,ans=[],[]
        def BackTrack(cur_index:int):
            if len(temp_ans)==k:
                ans.append(temp_ans[:])
            elif cur_index>n:
                return
            else:
                temp_ans.append(cur_index)
                BackTrack(cur_index+1)
                temp_ans.pop()
                BackTrack(cur_index+1)
        BackTrack(1)
        return ans