def verifyPreorder(self, preorder):
        left_finished = None
        stk = []
        for num in preorder:
            if left_finished and num < left_finished:
                return False

            while stk and stk[-1] < num:
                left_finished = stk.pop()

            stk.append(num)

        return True
Retrieve attribute value from given message database (server).
dataset/ETHPy150Open algorhythms/LeetCode/255 Verify Preorder Sequence in Binary Search Tree.py/Solution.verifyPreorder--crossover with--dataset/ETHPy150Open byt3bl33d3r/pth-toolkit/lib/python2.7/site-packages/openchange/mailbox.py/OpenChangeDB.get_message_attribute