generate-parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

[
  "((()))",
  "(()())",
  "(())()",
  "()(())",
  "()()()"
]

My code:
class Solution:
    def generateParenthesis(self, n):
        """
        :type n: int
        :rtype: List[str]
        """
        result=[]
        result=self.generateset(result,n)
        return result
    def generateset(self,result,n):
        if n==0:
            return
        if n==1: 
            result.append('()')
            return result
        result=self.generateset(result,n-1)
        #print('executing %d'%n)
        new_result=[]
        for i in range(len(result)):
            item=result[i]
            for j in range(len(item)):
                tmp_item=item[0:j]+'()'+item[j:]
                #print(tmp_item)
                if tmp_item not in new_result:
                    new_result.append(tmp_item)
        result=new_result
        return result
            
Solution:
https://leetcode.com/problems/generate-parentheses/