Decode String LeetCode solution in Python

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class Solution:
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    def decodeString(self, s: str) -> str:
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        stk = []
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        for i in range(len(s)):
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            if s[i] != "]":
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                stk.append(s[i])
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            else:
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                strr = ""
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                while stk[-1] != "[":
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                    strr = stk.pop() + strr
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                stk.pop()
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                num = ""
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                while stk and stk[-1].isdigit():
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                    num = stk.pop() + num
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                stk.append(int(num) * strr)
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        return "".join(stk)