[Python-Dev] PEP 557: Data Classes (original) (raw)

Eric V. Smith eric at trueblade.com
Mon Sep 11 21:36:21 EDT 2017

On 9/11/2017 6:28 PM, Guido van Rossum wrote:

Oddly I don't like the enum (flag names get too long that way), but I do agree with everything else Barry said (it should be a trivalue flag and please don't name it cmp).

So if we don't do enums, I think the choices are ints, strs, or maybe True/False/None. Do you have a preference here?

If int or str, I assume we'd want module-level constants.

I like the name compare=, and 3 values makes sense: None, Equality, Ordered.

Eric.

On Mon, Sep 11, 2017 at 3:16 PM, Ethan Furman <ethan at stoneleaf.us_ _<mailto:ethan at stoneleaf.us>> wrote: On 09/11/2017 03:00 PM, Barry Warsaw wrote: On Sep 10, 2017, at 20:08, Nathaniel Smith wrote:

I've sometimes wished that attrs let me control whether it generated equality methods (eq/ne/hash) separately from ordering methods (lt/gt/...). Maybe the cmp= argument should take an enum with options none/equality-only/full? I have had use cases where I needed equality comparisons but not ordered comparisons, so I’m in favor of the option to split them.  (atm, I can’t bring up a specific case, but it’s not uncommon.) Given that you only want to support the three states that Nathaniel describes, I think an enum makes the most sense, and it certainly would read well.  I.e. there’s no sense in supporting the ordered comparisons and not equality, so that’s not a state that needs to be represented. I’d make one other suggestion here: please let’s not call the keyword cmp.  That’s reminiscent of Python 2’s cmp built-in, which of course doesn’t exist in Python 3.  Using cmp is just an unnecessarily obfuscating abbreviation.  I’d suggest just compare with an enum like so: enum Compare(enum.Enum):  none = 1  unordered = 2  ordered = 3 I like the enum idea (suprise! ;) but I would suggest "equal" or "equivalent" instead of "unordered"; better to say what they are rather than what they are not. -- Ethan

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