How do i validate user input that starts with 2 numbers?

Question

I have tried to validate some input for my homework. Requirements:

• starts with 34 / 37 and has 15 digits: AMEX card
• starts with 4 and has 16 digits: VISA card

• if card number with 15 digits but does not start with 34, 37, print: You have entered an invalid Amex card numbers

• if card number with 16 digits but does not start with 4, print: You have entered an invalid Visa card numbers

• Card numbers that are not 15 or 16 digits, print: You have entered an invalid credit card number
• Once the card number has been validated, your program shall display the card type (Amex or Visa) and the last 4 digits of the credit card number.

I have tried to do len(number) to find the number of digits from user input. However, I keep getting the error "invalid syntax"

    number = int(input("Enter your credit card number :"))

    if len(number) = 16 and number.startswith(4):
        validity = "valid"
    if len(number) = 15 and number.startswith(34) and number.startswith(37):
        validity = "valid"
    else:
        validity = "invalid"

I cannot seem to get the correct outcome that I want.

This is how the program should run:

    Enter your credit card number : 432143214321432
    You have entered an invalid Amex card numbers
    Enter your credit card number : 3456345634563456
    You have entered an invalid Visa card numbers
    Enter your credit card number : 123
    You have entered an invalid credit card number
    Enter your credit card number : 4321432143214321
    You have a valid Visa card and the last 4 digit is 4321

Answer 1

if len(number) = 16 and number.startswith(4):

• len(number). Number does not have a len, so either convert number to a string here or don't convert it to an int in the first place
• number.startswith(4):. Same for this, ints do not have a startswith() method
• == is the comparison operator, not =

    number = input("Enter your credit card number :")

    if len(number) == 16 and number.startswith('4'):
        validity = "valid"
    if len(number) == 15 and number.startswith('34') or number.startswith('37'):
        validity = "valid"
    else:
        validity = "invalid"

If you need number as an int (unlikely for a credit card number) convert it with number = int(number)