Leetcode 1323. Maximum 69 Number

class Solution:
    def maximum69Number (self, num: int) -> int:
        num=str(num)
        tmp=[]
        for i in num: tmp.append(i)
        for i in range(len(tmp)):
            if tmp[i] =='6':
                tmp[i]='9'; 
                break
        ans=''
        for i in tmp: ans+=i
        return (int(ans))