Minimum Add to Make Parentheses Valid LeetCode solution in Python

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class Solution:
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    def minAddToMakeValid(self, s: str) -> int:
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        l, r = list(), list()
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        for i in s:
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            if i == "(":
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                l.append(i)
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            else:
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                if l:
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                    l.pop()
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                else:
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                    r.append(i)
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        return len(l) + len(r)