Replace All ?'s to Avoid Consecutive Repeating Characters LeetCode solution in Python

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class Solution:
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    def modifyString(self, s: str) -> str:
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        s = list(s)
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        abc = set(["a", "b", "c"])
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        for i, c in enumerate(s):
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            if c == "?":
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                neib = set()
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                if i != 0:
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                    neib.add(s[i - 1])
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                if i != len(s) - 1:
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                    neib.add(s[i + 1])
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                s[i] = (abc - neib).pop()
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        return "".join(s)