The input taken in by my program is wrong(logic error)

Question

this is my code:

cart = ['S/n'," "*10, 'Items', " " * 15, "Quantity", " " * 8, "Unit Price", " " * 6, "Price"]
total_pricee = 0
pricee = 0
count=1
def invalid_input(Quantitiy):
    while Quantitiy > '5' or Quantitiy < '1':
        Quantitiy = input("Please key in a valid quantity(Between 1 to 4):")
        if Quantitiy < '5' and Quantitiy > '1':
            New_Quan=Quantitiy
            break
    while not Quantitiy.isdigit():
        Quantitiy = input('Invalid input.Please enter a valid input:')
        while Quantitiy.isdecimal() == False:
            break
def add_to_cart(name, Quantity, price):
    global total_pricee, pricee,count
    cart.append('\n')
    cart.append('{:<10s}'.format(str(count)+'.'))
    cart.append('{:^10s}'.format(name))
    cart.append('{:^30s}'.format(Quantity))
    cart.append('{:^10s}'.format('$' + '{:.2f}'.format(float(price))))
    pricee = '{:.2f}'.format(float(Quantity) * price)
    cart.append('{:^23s}'.format('$' + str(pricee)))
    total_pricee += float(pricee)
    count = count +1
while True:
    print('[1] Water')
    print('[2] rice')
    print('[3] ice')
    print('[0] View Cart')
    opt = input("Select option:")
    if opt > '3' or opt < '0':
        print("Select valid option!")
    if opt == '3':
        qunt = input("How many would you like?")
        invalid_input(qunt)
        nam3 = "Ice"
        add_to_cart(nam3, qunt, 2)
    if opt == '1':
        qunt2 = input("How many would you like?")
        invalid_input(qunt2)
        nam2 = "Water"
        add_to_cart(nam2, qunt2, 3)
    if opt == '2':
        qunt1 = input("How many would you like?")
        invalid_input(qunt1)
        nam1 = "Rice"
        add_to_cart(nam1, qunt1, 5)
    if opt == "0":
        print(*cart)
        print("Total price until now:", "$" + '{:.2f}'.format(total_pricee))
        print('Would you like to check out?')
        print('[1] Yes')
        print('[2] No')
        checkout=input("Please select an option:")
        if checkout=='1':
            print('You have bought',count,'items')
            print("Please pay""$" + '{:.2f}'.format(total_pricee))
            print('Thank you for shopping with us!')
            exit()

The problem I am facing is that when the user enters a quantity more than 5(refer to invalid_input function), the program asks it to give a quantity less than 6.However, when I apply the add_to_cart, it takes the original value the user put in(which is greater than 5).

[1] Water
[2] rice
[3] ice
[0] View Cart
Select option:3
How many would you like?6
Please key in a valid quantity(Between 1 to 4):5
[1] Water
[2] rice
[3] ice
[0] View Cart
Select option:0
S/n            Items                 Quantity          Unit Price        Price 
 1.            Ice                   6                  $2.00            $12.00 

You see how it asked the user to key in a valid quantity(5) however the quantity taken by add_to_cartis the initial value(6).I want the quantity to display from the valid quantity.Help please!Thanks!

Answer 1

You just need to replace the > to >= to avoid the error in your logic,

def invalid_input(Quantitiy):
    #look the Qunatity>=5
    while Quantitiy >= '5' or Quantitiy < '1':
        Quantitiy = input("Please key in a valid quantity(Between 1 to 4):")
        if Quantitiy < '5' and Quantitiy > '1':
            New_Quan=Quantitiy
            break

what happens if you give only Qunatity> 5 and input 5 is that the condition becomes false.Because 5 is not greater than 5 itself.

Apart from this mistake when you were asking user to Please key in a valid quantity(Between 1 to 4) then you were not returning it back to your main module .Here is a modified version of your code,

#replaced cart with str1
str1="S/n\tItems\t  Quantity\tUnit Price\t\tPrice"
total_pricee = 0
pricee = 0
count=1
def invalid_input(Quantitiy):
    while Quantitiy >= '5' or Quantitiy < '1':
        Quantitiy = input("Please key in a valid quantity(Between 1 to 4):")
        if Quantitiy < '5' and Quantitiy > '1':
            New_Quan=Quantitiy

            #returned from here
            return Quantitiy

            break
    while not Quantitiy.isdigit():
        Quantitiy = input('Invalid input.Please enter a valid input:')
        while Quantitiy.isdecimal() == False:
            break
    #added the return here
    return Quantitiy

def add_to_cart(name, Quantity, price):
    global total_pricee, pricee,count,str1

    #replaced each cart statement with str1
    str1+="\n"
    str1+=str(count)+'.'+'\t'
    str1+=str(name)+'\t\t'
    str1+=str(Quantity)+'\t\t'
    str1+=str(price)+'\t\t'

    pricee = '{:.2f}'.format(float(Quantity) * price)
    pricee

    str1+=str(pricee)
    total_pricee += float(pricee)
    count = count +1
while True:
    print('[1] Water')
    print('[2] rice')
    print('[3] ice')
    print('[0] View Cart')
    opt = input("Select option:")
    if opt > '3' or opt < '0':
        print("Select valid option!")
    if opt == '3':
        qunt = input("How many would you like?")

        #getting the returned value to quant
        qunt =invalid_input(qunt)
        nam3 = "Ice"
        add_to_cart(nam3, qunt, 2)
    if opt == '1':
        qunt2 = input("How many would you like?")
        #getting the returned value to quant1
        qunt2=invalid_input(qunt2)
        nam2 = "Water"
        add_to_cart(nam2, qunt2, 3)
    if opt == '2':
        qunt1 = input("How many would you like?")

        #getting the returned value to quant1
        qunt1=invalid_input(qunt1)
        nam1 = "Rice"
        add_to_cart(nam1, qunt1, 5)
    if opt == "0":

        print(str1)
        print("Total price until now:", "$" + '{:.2f}'.format(total_pricee))
        print('Would you like to check out?')
        print('[1] Yes')
        print('[2] No')
        checkout=input("Please select an option:")
        if checkout=='1':
            print('You have bought',count,'items')
            print("Please pay""$" + '{:.2f}'.format(total_pricee))
            print('Thank you for shopping with us!')
            exit()

Hope this helps you!