Number of Wonderful Substrings LeetCode solution in Python

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class Solution:
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    def wonderfulSubstrings(self, word: str) -> int:
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        cnt, res, mask = [1] + [0] * 1023, 0, 0
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        for ch in word:
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            mask ^= 1 << (ord(ch) - ord("a"))
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            res += cnt[mask]
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            for n in range(10):
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                res += cnt[mask ^ 1 << n]
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            cnt[mask] += 1
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        return res