Python | Maintaining Grocery list

Problem Statement : 
Make a Grocery List for super market shopping with name, price and quantity; if the list already contains an item then only update the price and quantity it should not append the item name again. Ask user his/her budget initially 
and minus the budget after adding a new item in the list. If budgets go zero/0 then no more item could be bought and if some money left and user add item greater than budget left then inform “over price” or any other message. After the list is made any money left in the budget it should show an item within the budget from the list made. 
VALIDATION is a must.
Examples:

User GO with following question 
Enter Your budget : 500 
1.Add an item
2.Exit
Enter your choice : 1

Enter product : corn flour
Enter quantity : 1.5 kg
Enter Price : 100

Amount left : 400

1.Add an item
2.Exit
Enter your choice : 1

Enter product : wheat
Enter quantity : 2 kg
Enter Price : 100

Amount left : 300

1.Add an item
2.Exit
Enter your choice : 1

Enter product : corn flour
Enter quantity : 2 kg
Enter Price : 250

Amount left : 150

1.Add an item
2.Exit
Enter your choice : 1

Enter product : rice
Enter quantity : 5 kg
Enter Price : 300

Can't Buy the product ###(because budget left is 150)

1.Add an item
2.Exit
Enter your choice : 1

Enter product : xyz 
Enter quantity : 1 kg
Enter Price : 50

Amount left : 100

1.Add an item
2.Exit
Enter your choice : 2

Amount left can buy you wheat 

GROCERY LIST is:
Product name   Quantity   Price
corn flour      2 kg        250
wheat           2 kg        100
xyz             1 kg         50

Try to understand the above Problem statement and output explanation and try it yourself before going to the solution 

Code : Python code to check the Grocery List

Python3

# This loop will go on until the budget is integer or float
while True:
    try:
        bg = float(input("Enter your budget : "))
        # if budget is integer or float it will be stored
        # temporarily in variable 's'
        s = bg
    except ValueError:
        print("PRINT NUMBER AS A AMOUNT")
        continue
    else:
        break

# dictionary to store product("name"), quantity("quant"),
# price("price") with empty list as their values
a ={"name":[], "quant":[], "price":[]}

# converting dictionary to list for further updation
b = list(a.values())

# variable na value of "name" from dictionary 'a'
na = b[0]

# variable qu value of "quant" from dictionary 'a'
qu = b[1]

# variable pr value of "price" from dictionary 'a'
pr = b[2]

# This loop terminates when user select 2.EXIT option when asked
# in try it will ask user for an option as an integer (1 or 2)
# if correct then proceed else continue asking options
while True:
    try:
        ch = int(input("1.ADD\n2.EXIT\nEnter your choice : "))
    except ValueError:
        print("\nERROR: Choose only digits from the given option")
        continue
    else:
        # check the budget is greater than zero and option selected
        # by user is 1 i.e. to add an item
        if ch == 1 and s>0:

            # input products name
            pn = input("Enter product name : ")
            # input quantity of product
            q = input("Enter quantity : ")
            # input price of the product
            p = float(input("Enter price of the product : "))

            if p>s:
                # checks if price is less than budget
                print("\nCAN, T BUT THE PRODUCT")
                continue

            else:
                # checks if product name already in list
                if pn in na:
                    # find the index of that product
                    ind = na.index(pn)

                    # remove quantity from "quant"  index of the product
                    qu.remove(qu[ind])

                    # remove price from "price" index of the product
                    pr.remove(pr[ind])

                    # insert new value given by user earlier
                    qu.insert(ind, q)

                    # insert new value given by user earlier
                    pr.insert(ind, p)

                    # subtracting the price from the budget and assign
                    # it to 's' sum(pr) is because pr = [100, 200] if
                    # budget is 500 then s = bg-sum(pr) = 200
                    # after updating for same product at index 0 let
                    # pr = [200, 200] so s = 100
                    s = bg-sum(pr)

                    print("\namount left", s)
                else:
                    # append value of in "name", "quantity", "price"
                    na.append(pn)

                    # as na = b[0] it will append all the value in the
                    # list eg: "name":["rice"]
                    qu.append(q)

                    # same for quantity and price
                    pr.append(p)

                    # after appending new value the sum in price
                    # as to be calculated
                    s = bg-sum(pr)

                    print("\namount left", s)

        # if budget goes zero print "NO BUDGET"
        elif s<= 0:
            print("\nNO BUDGET")
        else:
            break

# will print amount left in variable 's'
print("\nAmount left : Rs.", s)

# if the amount left equals to any amount in price list
if s in pr:
    # then printing the name of the product which can buy
    print("\nAmount left can buy you a", na[pr.index(s)])

print("\n\n\nGROCERY LIST")

# print final grocery list
for i in range(len(na)):
    print(na[i], qu[i], pr[i])