如何将值添加到python字典中的现有值？

Question

I am once again seeking for your help in python where I am trying to add a value to an existing dictionary. Below I have my dictionary of items and a blank dictionary.

Dairy_goods = {1:{'item':'Milk','p':2.47,'g':0.16,'offer':'Yes','total':0},
        2:{'item':'Butter','p':4.50,'g':0.32,'offer':'No','total':0},
        3:{'item':'Egg','p':3.40,'g':0.24,'offer':'No','total':0}}

shopping_basket={}

I then set a if condition where if 'Milk' is selected it will be added into the shopping_basket{} dictionary

choose=int(input('1.Item= Milk, Price= $2.47, GST= $0.16, Offer=Yes\n'
                 '2.item= Butter, Price= $4.50, GST= $0.32, Offer=No\n'
                 '3.Item= Egg, Price= $4.50, GST= $0.32, Ofer=No\n'
                 'Enter your option: '))
qnty=int(input('How many do you want?: '))
price=(Dairy_goods[choose]['p'])
y = ((Dairy_goods[choose]['p']) * qnty)
gst = (Dairy_goods[choose]['g'])
offer = (Dairy_goods[choose]['offer'])

if choose==1:
    shopping_basket['Milk'] ={'Quantity': 0 + qnty, 'Individual price': price, 'total': y, 'GST': gst, 'offer': offer}
    # cart[Menu[choose]['item']] = cart.get(Menu[choose]['item'], 0) + qnty

But lets say I have already selected Milk once with a Quantity of 2, and if I would want to select it again to add on to the existing Quantity, it will not add on and would simply reset and give me the Value of the new keyed in quantity.

#example of output
How many Milk do you want?: 2
{'Milk': {'Quantity': 2, 'Individual price': 2.47, 'total': 2.47, 'GST': 0.16, 'offer': 'Yes'}}

#selecting Milk again

How many Milk do you want? : 3 
{'Milk': {'Quantity': 3, 'Individual price': 2.47, 'total': 2.47, 'GST': 0.16, 'offer': 'Yes'}} 
# at this point I should have a quantity for 5 but it does not add on to the existing value.

Answer 1

anyway you could do something like this using loops

Dairy_goods = {
    1: {"item": "Milk", "p": 2.47, "g": 0.16, "offer": "Yes", "total": 0},
    2: {"item": "Butter", "p": 4.50, "g": 0.32, "offer": "No", "total": 0},
    3: {"item": "Egg", "p": 3.40, "g": 0.24, "offer": "No", "total": 0},
}
shopping_basket = {}

while True:
    choose = int(
        input(
            "\n\n1.Item= Milk, Price= $2.47, GST= $0.16, Offer=Yes\n"
            "2.item= Butter, Price= $4.50, GST= $0.32, Offer=No\n"
            "3.Item= Egg, Price= $4.50, GST= $0.32, Ofer=No\n"
            "0.Exitthe program \n"
            "Enter your option: "
        )
    )

    if choose == 0:
        print("thanks!")
        break

    qnty = int(input("How many do you want?: "))
    price = Dairy_goods[choose]["p"]
    y = Dairy_goods[choose]["p"] * qnty
    gst = Dairy_goods[choose]["g"]
    offer = Dairy_goods[choose]["offer"]

    if choose == 1:
        if shopping_basket.get("Milk"):
            old_quan = shopping_basket["Milk"]["Quantity"]
        else:
            old_quan = 0
        shopping_basket["Milk"] = {
            "Quantity": old_quan + qnty,
            "Individual price": price,
            "total": y,
            "GST": gst,
            "offer": offer,
        }

    print(shopping_basket)

values will be reset on rerunning the program , to avoid this store it on file for that have look at this it may helps you more.