CS50P Jar类练习报错：构造函数传负容量未抛ValueError

你的代码核心问题是未对capacity的合法性做校验，同时部分方法的逻辑顺序错误，导致Check50检测失败。以下是具体修复点：

1. 给capacity添加合法性校验 #

当前的capacity setter直接赋值，没有判断传入值是否在0-12范围内。需要在setter中加入校验逻辑，确保构造函数传入负容量时抛出ValueError：

@capacity.setter
def capacity(self, capacity):
    if not isinstance(capacity, int) or capacity < 0 or capacity > 12:
        raise ValueError("Capacity must be an integer between 0 and 12")
    self._capacity = capacity

2. 修正deposit方法的逻辑 #

你当前是先修改size再判断是否超限，会导致size先变成非法值再抛错，且硬编码12而非使用self.capacity，不符合类的封装设计。正确逻辑是先判断再修改：

def deposit(self, n):
    if not isinstance(n, int) or n < 0:
        raise ValueError("Deposit amount must be a non-negative integer")
    if self.size + n > self.capacity:
        raise ValueError("Too many cookies to deposit")
    self.size += n

3. 修正withdraw方法的逻辑 #

同理，你当前先减size再判断是否为负，会导致size先变成负数再抛错。正确逻辑是先判断再修改：

def withdraw(self, n):
    if not isinstance(n, int) or n < 0:
        raise ValueError("Withdraw amount must be a non-negative integer")
    if self.size - n < 0:
        raise ValueError("Not enough cookies to withdraw")
    self.size -= n

4. 给size添加合法性校验 #

为防止直接设置self.size时出现非法值，需在size的setter中加入校验：

@size.setter
def size(self, size):
    if not isinstance(size, int) or size < 0 or size > self._capacity:
        raise ValueError("Size must be an integer between 0 and capacity")
    self._size = size

修复后的完整代码 #

class Jar:
    def __init__(self, capacity=12):
        self.capacity = capacity
        self.size = 0

    def __str__(self):
        return '🍪' * self.size

    def deposit(self, n):
        if not isinstance(n, int) or n < 0:
            raise ValueError("Deposit amount must be a non-negative integer")
        if self.size + n > self.capacity:
            raise ValueError("Too many cookies to deposit")
        self.size += n

    def withdraw(self, n):
        if not isinstance(n, int) or n < 0:
            raise ValueError("Withdraw amount must be a non-negative integer")
        if self.size - n < 0:
            raise ValueError("Not enough cookies to withdraw")
        self.size -= n

    @property
    def capacity(self):
        return self._capacity

    @property
    def size(self):
        return self._size

    @capacity.setter
    def capacity(self, capacity):
        if not isinstance(capacity, int) or capacity < 0 or capacity > 12:
            raise ValueError("Capacity must be an integer between 0 and 12")
        self._capacity = capacity

    @size.setter
    def size(self, size):
        if not isinstance(size, int) or size < 0 or size > self._capacity:
            raise ValueError("Size must be an integer between 0 and capacity")
        self._size = size

关键说明 #

• 构造函数传入负容量时，会触发capacity setter的校验，抛出ValueError，满足Check50检测要求。
• 所有状态修改操作先做合法性判断，再修改值，避免对象处于非法状态。
• 不再硬编码12，而是使用self.capacity，符合类的封装特性。

内容的提问来源于stack exchange，提问作者J Scott