leetcode Combination Sum II python

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the combination.

Note:
All numbers (including target) will be positive integers.
Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
The solution set must not contain duplicate combinations.
For example, given candidate set 10,1,2,7,6,1,5 and target 8,
A solution set is:
[1, 7]
[1, 2, 5]
[2, 6]
[1, 1, 6]
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class Solution(object):
    def combinationSum2(self, candidates, target):
        """
        :type candidates: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        candidates.sort()
        self.ret=[]
        self.dfs(candidates,target,0,[])
        return self.ret
    def dfs(self,candidates,target,start,valuelist):
        intlen=len(candidates)
        if target == 0 and valuelist not in self.ret:
            self.ret.append( valuelist)
        for i in range(start,intlen):
            if target < candidates[i]:
                return
            self.dfs(candidates,target-candidates[i],i+1,valuelist+[candidates[i]])