如何在Python中使用跳表算法进行查找

import random
import math

class SkipNode:
    def __init__(self, key=None, value=None):
        self.key = key
        self.value = value
        self.forward = []

class SkipList:
    def __init__(self, probability=0.5, max_level=32):
        self.head = SkipNode()
        self.probability = probability
        self.max_level = max_level

        self.head.forward = [None] * self.max_level

    def random_level(self):
        level = 1
        while random.random() < self.probability and level < self.max_level:
            level += 1
        return level

    def insert(self, key, value):
        update = [None] * self.max_level
        node = self.head

        for i in range(len(node.forward)-1, -1, -1):
            while node.forward[i] and node.forward[i].key < key:
                node = node.forward[i]

            update[i] = node

        node = node.forward[0]

        if node and node.key == key:
            node.value = value
        else:
            level = self.random_level()

            if level > len(self.head.forward):
                for i in range(len(self.head.forward), level):
                    update[i] = self.head
                    self.head.forward.append(None)

            node = SkipNode(key, value)

            for i in range(level):
                node.forward.append(None)

            for i in range(level):
                node.forward[i] = update[i].forward[i]
                update[i].forward[i] = node

    def search(self, key):
        node = self.head

        for i in range(len(node.forward)-1, -1, -1):
            while node.forward[i] and node.forward[i].key < key:
                node = node.forward[i]

        node = node.forward[0]

        if node and node.key == key:
            return node.value

        return None

    def delete(self, key):
        update = [None] * self.max_level
        node = self.head

        for i in range(len(node.forward)-1, -1, -1):
            while node.forward[i] and node.forward[i].key < key:
                node = node.forward[i]

            update[i] = node

        node = node.forward[0]

        if node and node.key == key:
            for i in range(len(node.forward)):
                update[i].forward[i] = node.forward[i]

            while len(self.head.forward) > 1 and not self.head.forward[-1]:
                self.head.forward.pop()

    def __repr__(self):
        nodes = []
        node = self.head.forward[0]

        while node:
            nodes.append((str(node.key), str(node.value)))
            node = node.forward[0]

        return str(nodes)

# Test it

list = SkipList()
keys = [3, 6, 9, 12, 15, 18, 21, 24, 27, 30]
values = ["three", "six", "nine", "twelve", "fifteen", "eighteen", "twenty-one", "twenty-four", "twenty-seven", "thirty"]

for i in range(len(keys)):
    list.insert(keys[i], values[i])

print(list.search(15))
list.delete(15)
print(list.search(15))
print(list)