| msg189854 - (view) |
Author: Alyssa Coghlan (ncoghlan) *  |
Date: 2013-05-23 08:56 |
| Another attempt at tackling the "but I want to ensure my enum values are unique" problem that PEP 435 deliberately chose not to handle. My previous suggestion (in issue 17959) was rightly rejected due to the other problems it caused, but this idea is much cleaner and simpler. All we would need to do is provide the following class decorator in the enum module: def unique(new_enum): for name, member in new_enum.__members__.items(): if name != member.name: msg = "Alias {!r} for {!r} not permitted in unique Enum" raise TypeError(msg.format(name, member)) return new_enum Used as so: >>> @enum.unique ... class MyEnum(enum.Enum): ... a = 1 ... b = 2 ... c = 1 ... Traceback (most recent call last): File "", line 2, in File "", line 6, in unique TypeError: Alias 'c' for <MyEnum.a: 1> not permitted in unique Enum |
|
|
| msg189881 - (view) |
Author: Ethan Furman (ethan.furman) * |
Date: 2013-05-23 22:23 |
| This is certainly an effective method, but it places safety off by default. I would rather have a system that was from duplicates by default but had an easy override. The method I had in place in my original code was something like: class Color(Enum, options=DUPLICATES): red = 1 green = 2 blue = 3 grene = 2 Without the DUPLICATES option, the above class would raise an error. Safe(r) by default, easy override. If my suggestion doesn't fly, we should definitely put Nick's in. |
|
|
| msg189883 - (view) |
Author: Alyssa Coghlan (ncoghlan) * |
Date: 2013-05-23 22:38 |
| I take Guido's acceptance of the PEP (and the discussion in the previous issue) as meaning the default behaviour (allowing aliases) is no longer up for debate. Hence this suggestion to offer a self-documenting way to opt in to the more restrictive variant. |
|
|
| msg189884 - (view) |
Author: Ethan Furman (ethan.furman) * |
Date: 2013-05-23 22:43 |
| I'm not giving up hope yet. Plenty of Python features no longer work the way they did when their PEP was accepted. ;) |
|
|
| msg189890 - (view) |
Author: Alyssa Coghlan (ncoghlan) * |
Date: 2013-05-24 02:53 |
| You don't generally see reversals of decisions where Guido has made an explicit choice based on consistency with the rest of the language. The fact that aliases are permitted in enumerations by default is consistent with the normal behaviour of namespaces and dictionaries in general, so providing a way to opt in to the stricter checks is a better solution. The idea of passing flags or other configuration options to the metaclass is also rather ugly. Offering permissive behaviour by default with an easy way to opt in to additional restrictions is far more in keeping with the general "consenting adults" ethos of the language. |
|
|
| msg189892 - (view) |
Author: Ethan Furman (ethan.furman) * |
Date: 2013-05-24 04:18 |
| Oh. Well, I like your decorator. :) |
|
|
| msg189894 - (view) |
Author: Alyssa Coghlan (ncoghlan) * |
Date: 2013-05-24 05:07 |
| Don't worry, compared to some of the ideas I've had (and rightfully had shot down) over the years, that one was positively sensible :) |
|
|
| msg190807 - (view) |
Author: Barry A. Warsaw (barry) * |
Date: 2013-06-08 16:38 |
| +1 for the decorator! |
|
|
| msg191450 - (view) |
Author: Ethan Furman (ethan.furman) * |
Date: 2013-06-19 06:49 |
| I haven't seen any discouraging words regarding the decorator. If no one has any compelling reasons why it shouldn't be added, I'll craft a version and put it in (only real difference with Nick's would be catching all the duplicates at once instead of one at a time). |
|
|
| msg191982 - (view) |
Author: Ethan Furman (ethan.furman) * |
Date: 2013-06-28 08:49 |
| unique() added to enum.py; tests added; docs updated. If no complaints within a few days I'll push them through. |
|
|
| msg191992 - (view) |
Author: Eli Bendersky (eli.bendersky) * |
Date: 2013-06-28 12:51 |
| Sent some review comments. I'll be on a short vacation this weekend, so please wait at least until next week so I can review the changes. Also, Nick should definitely review this too :) |
|
|
| msg192041 - (view) |
Author: Ethan Furman (ethan.furman) * |
Date: 2013-06-29 18:23 |
| Integrated comments. |
|
|
| msg192165 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2013-07-02 00:12 |
| The documentation still contains an "Interesting example": UniqueEnum. I would prefer to only have one obvious way to get unique enum, so please just drop this example. Or at least, mention the new decorator in the example. |
|
|
| msg193340 - (view) |
Author: Roundup Robot (python-dev)  |
Date: 2013-07-19 00:05 |
| New changeset 2079a517193b by Ethan Furman in branch 'default': closes -- a `unique` decorator is added to enum.py http://hg.python.org/cpython/rev/2079a517193b |
|
|