Longest Substring Without Repeating Characters LeetCode solution in Python

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class Solution:
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    def lengthOfLongestSubstring(self, s: str) -> int:
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        longest_s = ""
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        curr_s = ""
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        for i in s:
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            if i not in curr_s:
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                curr_s += i
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                if len(curr_s) >= len(longest_s):
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                    longest_s = curr_s
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            else:
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                curr_s = curr_s[curr_s.index(i) + 1 :] + i
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        return len(longest_s)