unreasonably effective

class Solution:
    def largestOddNumber(self, num: str) -> str:
        odd_digits = {"1", "3", "5", "7", "9"}
        lsb = len(num)-1
        while lsb >= 0:
            if num[lsb] in odd_digits:
                break
            lsb -= 1
        return num[:lsb+1]