Find Lucky Integer in an Array LeetCode solution in Python

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class Solution:
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    def findLucky(self, arr: List[int]) -> int:
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        dc = {}
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        for i in range(len(arr)):
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            if arr[i] not in dc:
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                dc[arr[i]] = 1
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            else:
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                dc[arr[i]] = dc[arr[i]] + 1
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        mx = -1
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        for key, value in dc.items():
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            if key == value:
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                mx = max(key, mx)
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        return mx