如何在Python中更新嵌套字典：添加quantity键值对

通过输入选择字典的键，为对应的嵌套字典添加一个quantity键值对。

尝试代码：

menu = {
    1: {"item": "Green Beret Omelette", "price": "$12.99"},
    2: {"item": "Get to the Chopped Salad", "price": "$14.99"},
    3: {"item": "Pump You Up Protein Shake", "price": "$9.99"},
    4: {"item": "I'll Be Baby Back Ribs", "price": "$22.99"},
    5: {"item": "Let Off Some Steamed Vegetables", "price": "$4.99"},
    6: {"item": "The Ice Cream Cometh", "price": "$15.99"}
}

selection = int(input("Please select your item:\n"))
if int(selection) < 1 or int(selection) > 6:
    print("Invalid selection. Please try again. \n")

count = int(input("Enter quantity: \n"))

# This is the line I'd like help with
menu[selection].update["quantity": count]

需要修改menu[selection].update["quantity": count]，使menu更新为包含选中条目quantity键值对的形式。

修改方案 #

问题出在update方法的调用方式上，Python字典的update()是方法，需传入字典参数并通过括号调用，而非方括号。有两种简洁的修改方式：

1. 直接赋值（最推荐）
   直接通过键访问嵌套字典，为quantity键赋值：

menu[selection]["quantity"] = count

2. 正确使用update()方法
   若要使用update，需传入包含目标键值对的字典，并用括号调用方法：

menu[selection].update({"quantity": count})

优化后的完整代码 #

原代码存在输入无效时仍会执行后续操作的问题，可能引发KeyError，这里调整验证逻辑：

menu = {
    1: {"item": "Green Beret Omelette", "price": "$12.99"},
    2: {"item": "Get to the Chopped Salad", "price": "$14.99"},
    3: {"item": "Pump You Up Protein Shake", "price": "$9.99"},
    4: {"item": "I'll Be Baby Back Ribs", "price": "$22.99"},
    5: {"item": "Let Off Some Steamed Vegetables", "price": "$4.99"},
    6: {"item": "The Ice Cream Cometh", "price": "$15.99"}
}

selection = int(input("Please select your item:\n"))
if 1 <= selection <= 6:
    count = int(input("Enter quantity: \n"))
    # 使用直接赋值方式添加quantity
    menu[selection]["quantity"] = count
else:
    print("Invalid selection. Please try again. \n")

# 打印验证结果
print(menu)

执行后选中条目会新增quantity键值对，符合预期格式。

内容的提问来源于stack exchange，提问作者Jamie.Sgro