python - 代码追踪和逻辑错误

Question

class MyHashTable:

    def __init__(self, capacity):
        self.capacity = capacity
        self.slots = [None] * self.capacity

    def __str__(self):
        return str(self.slots )

    def __len__(self):
        count = 0
        for i in self.slots:
            if i != None:
                count += 1
        return count

    def hash_function(self, key):
        slot = key % len(self.slots)

        if key in self.slots:
            return slot

        elif (not key in self.slots) and len(self.slots) == self.capacity:
            return slot

        else:
            for i in self.slots:
                count = 0 
                if i == None:
                    return count
                count += 1

    def insert(self, key):
        print(len(self.slots)) #Why does this show an output of 2? 
        if key in self.slots:
            return -2

        elif (not key in self.slots) and (len(self.slots) != self.capacity): #Now this cant execute
            num = hash_function(key)
            self.slots[num] = key
            return num

        elif (not key in self.slots) and len(self.slots) == self.capacity:
            return -1

我想知道为什么上面的 insert(self, key) 打印语句中的注释部分给出 (2) 而不是 (0)。下面的 elif 语句不会执行，因为它给出的结果是 (2) 而不是 (0)

函数调用

x = MyHashTable(2)
print(len(x)) 

应给出:0

Answer 1

您正在初始化 self.slots = [None] * self.capacity，因此使用 capacity = 2，self.slots 为[None, None]，长度为 2。

您的 __len__ 方法未运行，因为 len(self.slot) 调用 self.slot.__len__，而不是 self .__len__。如果您想使用重写方法，则应该调用 len(self)。