Project: Credit Card Mask
Write a function that takes a credit card number in the format "1234 5678 9012 3456" and returns a string with all but the last four digits replaced with an "X". Use a regular expression to match a group of four digits followed by a space and replace them with "XXXX ".
Output
$ python3 CreditCardMask.py
XXXX XXXX XXXX 3456
XXXX XXXX XXXX 1929
XXXX XXXX XXXX 3902