Python: comprehension inside a class error

Question

My issue is that whenever I try to add the below code in a class, I get an error. Using it outside of the class seem to work just fine. What is the reason of this? Thanks!

class Deck:
    used_suits = ["D", "H", "C", "S"]
    used_numbers = [i for i in range (2, 11)]
    used_cards = [str(number) for number in used_numbers] + ["J", "Q", "K", "A"]
    all_cards = [number + letter for number in used_cards for letter in used_suits]

Output:

all_cards = [number + letter for number in used_cards for letter in used_suits]
                                                                        ^^^^^^^^^^
NameError: name 'used_suits' is not defined