Credit

Implement a program that determines whether a provided credit card number is valid according to Luhn’s algorithm.

$ python credit.py
Number: 378282246310005
AMEX

Getting Started

Log into code.cs50.io, click on your terminal window, and execute cd by itself. You should find that your terminal window’s prompt resembles the below:

Next execute

wget https://cdn.cs50.net/2022/fall/psets/6/sentimental-credit.zip

in order to download a ZIP called sentimental-credit.zip into your codespace.

Then execute

unzip sentimental-credit.zip

to create a folder called sentimental-credit. You no longer need the ZIP file, so you can execute

rm sentimental-credit.zip

and respond with “y” followed by Enter at the prompt to remove the ZIP file you downloaded.

Now type

cd sentimental-credit

followed by Enter to move yourself into (i.e., open) that directory. Your prompt should now resemble the below.

sentimental-credit/ $

Execute ls by itself, and you should see credit.py. If you run into any trouble, follow these same steps again and see if you can determine where you went wrong!

If you’d like to open this problem in CS50 Lab, you can right-click or control-click on the sentimental-credit folder and choose “Open in CS50 Lab”. You should see the specification for this problem on the left-hand side and its distribution code on the right-hand side.

Specification

In credit.py, write a program that prompts the user for a credit card number and then reports (via print) whether it is a valid American Express, MasterCard, or Visa card number, exactly as you did in Problem Set 1, except that your program this time should be written in Python.
So that we can automate some tests of your code, we ask that your program’s last line of output be AMEX\n or MASTERCARD\n or VISA\n or INVALID\n, nothing more, nothing less.
For simplicity, you may assume that the user’s input will be entirely numeric (i.e., devoid of hyphens, as might be printed on an actual card).
Best to use get_int or get_string from CS50’s library to get users’ input, depending on how you to decide to implement this one.

Usage

Your program should behave per the example below.

$ python credit.py
Number: 378282246310005
AMEX

Hints

It’s possible to use regular expressions to validate user input. You might use Python’s re module, for example, to check whether the user’s input is indeed a sequence of digits of the correct length.

Testing

While check50 is available for this problem, you’re encouraged to first test your code on your own for each of the following.

Run your program as python credit.py, and wait for a prompt for input. Type in 378282246310005 and press enter. Your program should output AMEX.
Run your program as python credit.py, and wait for a prompt for input. Type in 371449635398431 and press enter. Your program should output AMEX.
Run your program as python credit.py, and wait for a prompt for input. Type in 5555555555554444 and press enter. Your program should output MASTERCARD.
Run your program as python credit.py, and wait for a prompt for input. Type in 5105105105105100 and press enter. Your program should output MASTERCARD.
Run your program as python credit.py, and wait for a prompt for input. Type in 4111111111111111 and press enter. Your program should output VISA.
Run your program as python credit.py, and wait for a prompt for input. Type in 4012888888881881 and press enter. Your program should output VISA.
Run your program as python credit.py, and wait for a prompt for input. Type in 1234567890 and press enter. Your program should output INVALID.

Execute the below to evaluate the correctness of your code using check50. But be sure to compile and test it yourself as well!

check50 cs50/problems/2022/fall/sentimental/credit

Execute the below to evaluate the style of your code using style50.

style50 credit.py

How to Submit

Download your credit.py file by control-clicking or right-clicking on the file in your codespace’s file browser and choosing Download.
Go to CS50’s Gradescope page.
Click “Problem Set 6: Sentimental (Credit)”.
Drag and drop your credit.py file to the area that says “Drag & Drop”. Be sure it has that exact filename! If you upload a file with a different name, the autograder likely will fail when trying to run it, and ensuring you have uploaded files with the correct filename is your responsibility!
Click “Upload”.

You should see a message that says “Problem Set 6: Sentimental (Credit) submitted successfully!” You may not see a score just yet, but if you see the message then we’ve received your submission!

Per Step 4 above, after you submit, be sure to check your autograder results. If you see SUBMISSION ERROR: missing files (0.0/1.0), it means your file was not named exactly as prescribed (or you uploaded it to the wrong problem).

Correctness in submissions entails everything from reading the specification, writing code that is compliant with it, and submitting files with the correct name. If you see this error, you should resubmit right away, making sure your submission is fully compliant with the specification. The staff will not adjust your filenames for you after the fact!