Constant class attribute style according to PEP8: uppercase or lowercase?

Question

I really like to follow the standard coding style, but can't find an answer on this.

class Card:
    """Card class representing a playing card."""
    RANKS = (None, 'Ace', '2', '3', '4', '5', '6', '7', '8', '9', '10',
             'Jack', 'Queen', 'King')
    SUITS = ('Clubs', 'Spades', 'Diamonds', 'Hearts')

    def __init__(self, rank, suit):
        self.rank = rank
        self.suit = suit

    def __str__(self):
        return f"{Card.RANKS[self.rank]} of {Card.SUITS[self.suit]}"


c = Card(1, 1)
print(c)

Should I write constants in class attributes all_lower_case or ALL_UPPER_CASE? PEP8 just says that constants should be ALL_UPPER_CASE at the module level. What about classes?

Answer 1

PEP8 makes it clear that constants should be upper-case:

Constants

Constants are usually defined on a module level and written in all capital letters with underscores separating words. Examples include MAX_OVERFLOW and TOTAL.

Note that it just says that these are usually defined on a module level. But if your values should be treated as constants then make them uppercase - even if they are defined on a class level.

Answer 2

Why not extract those outside of the class in the module like this:

from enum import Enum

class Suit(Enum):
    CLUBS = 1
    SPADES = 2
    DIAMONDS = 3
    HEARTS = 4

Then you could use it like:

Card(Rank.1, Suit.SPADES)

Also according to the following Python documentation it's ALL_CAPS, even inside Class. This also makes sense to me.

More info and examples.