Basic Calculator LeetCode solution in Python

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# Runtime: 137 ms (Top 57.95%) | Memory: 15.5 MB (Top 50.78%)
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class Solution:
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    def calculate(self, s: str) -> int:
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        curr, output, sign, stack = 0, 0, 1, []
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        for ch in s:
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            if ch.isdigit():
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                curr = curr * 10 + int(ch)
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            elif ch == "+":
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                output += sign * curr
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                sign = 1
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                curr = 0
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            elif ch == "-":
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                output += sign * curr
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                sign = -1
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                curr = 0
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            elif ch == "(":
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                # push the result and then the sign
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                stack.append(output)
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                stack.append(sign)
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                sign = 1
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                output = 0
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            elif ch == ")":
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                output += sign * curr
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                output *= stack.pop()
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                output += stack.pop()
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                curr = 0
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        return output + sign * curr