Find All Duplicates in an Array LeetCode solution in Python

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class Solution:
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    def findDuplicates(self, nums: List[int]) -> List[int]:
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        res = []
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        hm = {}
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        # adding entries in hashmap to check frequency
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        for i, v in enumerate(nums):
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            if v not in hm:
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                hm[v] = 1
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            else:
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                hm[v] += 1
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        # checking frequency of item and adding output to an array
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        for key, value in hm.items():
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            if value > 1:
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                res.append(key)
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        return res