Skip to content

Problem 1: Vending Machine (100pts)

Problem

Create a class called VendingMachine that represents a vending machine for some product. A VendingMachine object returns strings describing its interactions. Fill in the VendingMachine class, adding attributes and methods as appropriate, such that its behavior matches the following doctests:

创建一个名为 VendingMachine 的类，用于表示某种产品的自动售货机。VendingMachine 对象返回描述其交互的字符串。 填充 VendingMachine 类，添加适当的属性和方法，使其行为与以下 doctests 匹配：

class VendingMachine:
    """A vending machine that vends some product for some price.

    >>> v = VendingMachine('candy', 10)
    >>> v.vend()
    'Machine is out of stock.'
    >>> v.add_funds(15)
    'Machine is out of stock. Here is your $15.'
    >>> v.restock(2)
    'Current candy stock: 2'
    >>> v.vend()
    'You must add $10 more funds.'
    >>> v.add_funds(7)
    'Current balance: $7'
    >>> v.vend()
    'You must add $3 more funds.'
    >>> v.add_funds(5)
    'Current balance: $12'
    >>> v.vend()
    'Here is your candy and $2 change.'
    >>> v.add_funds(10)
    'Current balance: $10'
    >>> v.vend()
    'Here is your candy.'
    >>> v.add_funds(15)
    'Machine is out of stock. Here is your $15.'

    >>> w = VendingMachine('soda', 2)
    >>> w.restock(3)
    'Current soda stock: 3'
    >>> w.restock(3)
    'Current soda stock: 6'
    >>> w.add_funds(2)
    'Current balance: $2'
    >>> w.vend()
    'Here is your soda.'
    """

    def __init__(self, product: str, price: int):
        """Set the product and its price, as well as other instance attributes."""
        "*** YOUR CODE HERE ***"

    def restock(self, quantity: int) -> str:
        """Add quantity to the stock and return a message about the updated stock level.

        E.g., Current candy stock: 3
        """
        assert quantity > 0
        "*** YOUR CODE HERE ***"

    def add_funds(self, funds: int) -> str:
        """If the machine is out of stock, return a message informing the user to restock
        (and return their n dollars).

        E.g., Machine is out of stock. Here is your $4.

        Otherwise, add funds to the balance and return a message about the updated balance.

        E.g., Current balance: $4
        """
        "*** YOUR CODE HERE ***"

    def vend(self) -> str:
        """Dispense the product if there is sufficient stock and funds and
        return a message. Update the stock and balance accordingly.

        E.g., Here is your candy.
        E.g., Here is your candy and $2 change.

        If not, return a message suggesting how to correct the problem.

        E.g., Machine is out of stock.
        E.g., You must add $3 more funds.
        """
        "*** YOUR CODE HERE ***"

Hints

Hint1: You may find Python string formatting syntax or f-strings useful. A quick example:

>>> ten, twenty, thirty = 10, 'twenty', [30]
>>> '{0} plus {1} is {2}'.format(ten, twenty, thirty)
'10 plus twenty is [30]'

>>> feeling = 'love'
>>> course = 'SICP'
>>> year = 2025
>>> f'I {feeling} {course}-{year}!'
'I love SICP-2025!'

Hint2: Make sure to handle corner cases, such as trying to vend when the machine is out of stock.

Hint3: For the ease of understanding, we provide type hints for each parameter in every method. For example, quantity: int and product: str indicate that quantity will be an integer, while product will be a string. For functions (or methods), def vend(self) -> str indicates that vend() should return a string. You can assume that all inputs to the methods will be of the correct type. You do not need to handle invalid input types.

>>> ten, twenty, thirty = 10, 'twenty', [30]
>>> '{0} plus {1} is {2}'.format(ten, twenty, thirty)
'10 plus twenty is [30]'

>>> feeling = 'love'
>>> course = 'SICP'
>>> year = 2025
>>> f'I {feeling} {course}-{year}!'
'I love SICP-2025!'

  • 确保处理边界情况，例如机器缺货时尝试售卖。

  • 为了方便理解，我们为每个方法中的每个参数提供了 类型提示。 例如，quantity: int 和 product: str 表示 quantity 将是一个整数，而 product 将是一个字符串。 对于函数（或方法），def vend(self) -> str 表示 vend() 应该返回一个字符串。 您可以假设输入给方法的所有输入都将是正确的类型。您不需要处理无效的输入类型。