Minimum Remove to Make Valid Parentheses LeetCode solution in Python

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class Solution:
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    def minRemoveToMakeValid(self, s):
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        stack = []
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        split_str = list(s)
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        for i in range(len(s)):
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            if s[i] == "(":
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                # if current char is '(' then push it to stack
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                stack.append(i)
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            elif s[i] == ")":
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                # if current char is ')' then pop top of the stack
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                if len(stack) != 0:
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                    stack.pop()
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                else:
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                    # if our stack is empty then we can't pop so make  current char as ''
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                    split_str[i] = ""
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        for i in stack:
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            split_str[i] = ""
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        return "".join(split_str)