app.py

import gradio as gr

def check_credit_card(card_number: str):
    card_number = card_number.replace(" ", "")  # remove spaces
    if not card_number.isdigit():  # check if the input is numeric
        return "Invalid input. Please enter a numeric credit card number."
    card_number = int(card_number)
    # convert card number to string to easily calculate its length
    card_number_str = str(card_number)
    digit = len(card_number_str)

    # check if the card number has a valid length
    if digit != 13 and digit != 16 and digit != 15:
        return "INVALID"

    # split the card number into individual digits and store them in a list
    number = [int(x) for x in card_number_str[::-1]]

    original_number = number.copy()  # create a copy of the number list

    # apply Luhn's algorithm
    for i in range(1, digit, 2):
        original_number[i] *= 2

    # sum the digits of the numbers in original_number
    v = sum(sum(divmod(x, 10)) for x in original_number)

    # check if the card is a Visa, MasterCard, or American Express card
    if digit == 13:
        if number[-1] == 4 and v % 10 == 0:
            return "VISA"
    elif digit == 15:
        if number[-1] == 3 and v % 10 == 0 and number[-2] in [4, 7]:
            return "AMEX"
    elif digit == 16:
        if number[-1] == 4 and v % 10 == 0:
            return "VISA"
        elif number[-1] == 5 and v % 10 == 0 and number[-2] in [1, 2, 3, 4, 5]:
            return "MASTERCARD"

    return "INVALID"

iface = gr.Interface(fn=check_credit_card,
                     inputs=gr.inputs.Textbox(label="Credit Card Number"),
                     outputs="text",
                     layout="vertical",
                     title="Arasy's credit/debit card checker"
                    )

iface.launch()