在python中遍历列表中的树来进行计算？

def calculate_tree(tree):
    if isinstance(tree, int):
        return tree
    elif isinstance(tree, list):
        if tree[0] == '+':
            return calculate_tree(tree[1]) + calculate_tree(tree[2])
        elif tree[0] == '-':
            return calculate_tree(tree[1]) - calculate_tree(tree[2])
        elif tree[0] == '*':
            return calculate_tree(tree[1]) * calculate_tree(tree[2])
        elif tree[0] == '/':
            return calculate_tree(tree[1]) / calculate_tree(tree[2])
    else:
        raise ValueError("Invalid tree format")

# 示例用法
tree = ['+', 1, ['*', 2, 3]]
result = calculate_tree(tree)
print(result)  # 输出结果为 7