My while loop doesn't loop in my code when user input an invalid character like a space, nothing, special characters, and and letters [duplicate]

Question

I am trying to make a credit card checker which displays whether the input aka the card number is invalid, Mastercard, visa, or Amex.

i want the code to re ask the user to enter a number if a user enters any letters, special characters, spaces, or nothing. But in the code for Luhn's algorithm i have to change the "inp" to a int to multiply but then the code ends with an error then if the input contains any invalid input. How can I make it prompt again if the input is invalid?

while True:

    inp = (input("Enter a number!: "))

    inp_1 = inp[0::]
    inp_2 = inp[0::]
    inp_3 = inp[0::]
    inp_4 = inp[0::]

    reversed_inp = inp[::-1]

    inp = reversed_inp[1::2]


    value = 0
    inp = str(inp)
    for character in inp:
        character = int(character)
        character *= 2
        character = str(character)
        character = int(character)
        for i in range(len(str(character))):
            digit = character%10
            value = value + digit
            character = character//10

    reversed_inp_2 = inp_1[::-1]

    inp_1 = reversed_inp_2[0::2]

    value_1 = 0
    
    for numbers in inp_1:
        numbers = int(numbers)
        
        
        value_1 = value_1 + numbers

    final_value = value_1 + value

    final_value = str(final_value)
    reversed_final_value = final_value[::-1]

    zero_checker = reversed_final_value[0:1:]
    zero_checker = (zero_checker)


    if zero_checker == 1 or  zero_checker == 2 or zero_checker == 3 or zero_checker == 4 or zero_checker == 5 or zero_checker == 6 or zero_checker == 7 or zero_checker == 8 or zero_checker == 9:
        print("INVALID")
        break
   
    def countDigits(inp_3):
        dcount = 0
        for c in inp_3:
            if c.isdigit():
                dcount = dcount + 1
        return dcount
    
    digits = countDigits(inp_3)
    digits = str(digits)


    Amex_checker = inp_2[0:2:]
    Amex_checker = str(Amex_checker)
    MasterCard_checker = inp_2[0:2:]
    MasterCard_checker = str(MasterCard_checker)
    Visa_Checker = inp_2[0:1:]
    Visa_Checker = str(Visa_Checker)

    if Amex_checker == "34" and digits == "15":
        print("AMEX")
        break
    elif Amex_checker == "37" and digits == "15":
        print("AMEX")
        break

    if MasterCard_checker == "51" and digits == "16":
        print("MASTERCARD")
        break
    elif MasterCard_checker == "52" and digits == "16":
        print("MASTERCARD")
        break
    elif MasterCard_checker == "53" and digits == "16":
        print("MASTERCARD")
        break
    elif MasterCard_checker == "54" and digits == "16":
        print("MASTERCARD")
        break
    elif MasterCard_checker == "55" and digits == "16":
        print("MASTERCARD")
        break

    if Visa_Checker == "4" and digits == "16" or digits == "13":
        print("VISA")
        break

Welcome to Stack Overflow. "i added the while true loop its just that i am new to stack overflow and it is not showing in the code for some reason but everything is in the while loop." Please read How to Ask and especially the formatting help. Note well that this is not a discussion forum. I edited the post to show how to ask a bit more directly and clearly, but the question is still a mess. When posting here, please try to come up with sample code that directly demonstrates the problem; don't just show us the entire original code. See minimal reproducible example. — Karl Knechtel
– Karl Knechtel, Commented Oct 5, 2022 at 1:34

H.Syd · Accepted Answer · 2022-10-05 01:30:00Z

0

This asks the user to enter a number until it is a valid integer:

user_in = None
while user_in is None:
    try:
        user_in = int(input("Give me a number:"))
    except ValueError:
        print("Invalid input.")

You could edit one line, to get a valid string, instead of an int:

user_in = str(int(input("Give me a number:")))

answered Oct 5, 2022 at 1:30

H.Syd

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