ATM PIN Code Validation

ATM machines allow 4 or 6 digit PIN codes and PIN codes cannot contain anything but exactly 4 digits or exactly 6 digits. Your task is to create a function that takes a string and returns True if the PIN is valid and False if it's not.

Examples

is_valid_PIN("1234") ➞ True

is_valid_PIN("12345") ➞ False

is_valid_PIN("a234") ➞ False

is_valid_PIN("") ➞ False

Notes

• Some test cases contain special characters.
• Empty strings must return False.