Adding Spaces to a String LeetCode solution in Python

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class Solution:
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    def addSpaces(self, s: str, spaces: List[int]) -> str:
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        arr = []
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        prev = 0
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        for space in spaces:
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            arr.append(s[prev:space])
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            prev = space
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        arr.append(s[space:])
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        return " ".join(arr)