将单个键值对从一个字典移动到另一个字典

Question

我正在用 python 建立一个基本的商店，里面有一个项目及其价格的字典。我正在为购物车使用字典，我希望用户能够将商品添加到购物车。为此，我的目标是将产品字典中的键和值复制到购物车字典。我怎样才能做到这一点？products = {"Pencil": 1, "Notebook": 2, "Backpack": 3, "Pens": 2, "Markers": 5, "Whiteboard": 30}cart = {}def addToCart():    productToAdd = input("What would you like to add? ")    for k,v in products.items():        if productToAdd == k:            price = v            cart[productToAdd] = cart[v]            break

Answer 1

products = {"Pencil": 1, "Notebook": 2, "Backpack": 3, "Pens": 2, "Markers": 5, "Whiteboard": 30}

cart = {}

def addToCart():

    try:

        productToAdd = input("What would you like to add? ")

        cart[productToAdd]=products[productToAdd]

    except KeyError:

        print("No such product")

请注意，python 区分大小写 'pencil' 和 'Pencil' 不一样。如果您确定产品首先是大写字母，您可以使用

productToAdd = input("What would you like to add? ").title()

Answer 2

您可以使用dict.setdefault(key, default=None)

示例：

def addToCart():

    productToAdd = input("What would you like to add? ")

    cart[productToAdd]=products.setdefault(productToAdd, 'No such product')

Answer 3

假设用户将从该列表中选择项目（特别是从键），然后：

products = {"Pencil": 1, "Notebook": 2, "Backpack": 3, "Pens": 2, "Markers": 5, 

"Whiteboard": 30}

cart = {}

def addToCart():

    productToAdd = input("What would you like to add? ")

    if not productToAdd.title() in products: # for removing caps confusion

        print('No such item')

    else: cart[productToAdd] = products[productToAdd]

>>> addToCart()

What would you like to add? Pencil

>>> cart

{'Pencil': 1}