[docs] [issue27877] Add recipe for "valueless" Enums to docs

[Raymond Hettinger]

Raymond Hettinger added the comment:

-0 I concur with OP's observation that "object() returns a new unique value while conveying that that value should not be expected to be used in any meaningful way" and that this recipe could help reinforce that notion.  That said, the idiomatic way to communicate this in Python is to use None rather than to create distinct meaningless objects.

Also, the motivation seems questionable.  Instead of showing a real world case where some confusion exists, there seems to be a general irritation that Enum implementation details differ in some respects from various compiled languages.  ISTM, the recipe is aimed at an imagined problem rather than an actual problem -- in a real use case (not a toy Color example), I would expect that if the value field is meaningless, then the use case itself will tend to make it self-evident that there is no reason to access the value field (and if it didn't, I don't see how returning some arbitrary instance of object() would be more informative than returning None.)

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nosy: +rhettinger

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<https://bugs.python.org/issue27877>
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