Adding Spaces to a String

class Solution:
    def addSpaces(self, s: str, spaces: List[int]) -> str:
        # to make searching time constant
        spaces=set(spaces)
        # the variable to keep my answer
        answer=""
        length=len(s)
        for index in range(length):
            if index in spaces:
                answer+= " " + s[index]
                continue
            answer += s[index]
        return answer