需要帮助理解python中的字典

Question

I'm new to coding and wrote a script. I can't understand why the total being displayed is wrong and changes each time I run the program. I know that dictionaries do not store the key and value in the same order each time but I don't understand why the totals are wrong and never the same? Can someone help? I'm looking for an explanation so I can learn from my mistake.

stock = [["mp40", 4], ["crowbar", 3], ["machete", 4], ["5_person_tent", 3],
         ["gps", 10], ["duffle_bag", 3], ["first_aid_kit", 2], ["horse", 1],
         ["military_mre", 7], ["camping_stove", 1], ["hunting_vest", 2],
         ["jogging_pants", 3], ["timberlands", 2], ["gas_generator", 3],
         ["gasoline", 500], ["gas_can", 100], ["pontiac_grand_dam", 1]]

prices = [["mp40", 390], ["crowbar", 20], ["machete",40],["5_person_tent",250],
          ["gps", 97], ["duffle_bag",20], ["first_aid_kit",15], ["horse", 3000],
          ["military_mre",15],["camping_stove",15], ["hunting_vest", 60],
          ["jogging_pants", 60], ["timberlands", 150], ["gas_generator",180],
          ["gasoline", 3],["gas_can", 20], ["pontiac_grand_dam", 2000]]


def buy():
    purchase =input("What item you want to buy?\n")
    total = 0
    for item in stock:
        if purchase in stock.keys(): 
            if stock[item] > 0:
                amount =int(input("How many would you like to purchase?\n"))
                total += (prices[item]*(amount))
                stock[item] -=(amount)
                print ('You owe'+' '+'$'+str(total))
                input('press enter to continue \n')
                return total

            if stock[item]<1:
                print ("we don't have any left\n")

        if purchase!=item:
            print ("We do not sell that.\n")

a=0
while a==0:
    buy()

Answer 1

You need to make stock and prices dictionaries, not lists. Fortunately, your current data makes this easy, as dict can take a list of key-value pairs as an argument. That is,

stock = [...]   # current definition
stock = dict(stock)

prices = [ ... ] # current definition
prices = dict(prices)

Defining the dictionary "manually" would look something like

stock = {"mp40":4,
         "crowbar":3,
         "machete":4, } # etc