Evaluate Division LeetCode solution in Python

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class Solution:
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    def calcEquation(
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        self, equations: List[List[str]], values: List[float], queries: List[List[str]]
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    ) -> List[float]:
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        graph = dict()
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        for (n, d), v in zip(equations, values):
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            if n not in graph:
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                graph[n] = []
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            if d not in graph:
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                graph[d] = []
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            graph[n].append((d, v))
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            graph[d].append((n, 1 / v))
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        def dfs(node, target, product, visited):
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            if n not in graph or d not in graph:
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                return -1
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            if node == target:
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                return product
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            visited.add(node)
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            for neighbor, quotient in graph[node]:
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                if neighbor not in visited:
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                    soln = dfs(neighbor, target, product * quotient, visited)
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                    if soln != -1:
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                        return soln
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            return -1
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        solns = []
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        for n, d in queries:
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            solns.append(dfs(n, d, 1, set()))
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        return solns