Steven D'Aprano wrote: > On Sat, Nov 30, 2019 at 08:24:39AM -0000, Steve Jorgensen wrote: > > Basically, with the current implementation of > > Enum and supporting > > classes, the only way that a member can have access to its own name > > during or prior to its initialization is if/when its value is > > auto-generated, so if you want to specify a value rather than having > > it auto-generated (e.g. to generate a label attribute) then there's no > > convenient way to do it. > > Code speaks louder than words. Can you give an example of what you are > trying to do? If I'm reading you correctly, we can already specify > values: > py> class Colours(Enum): > ... red = auto() > ... green = 999 > ... > py> Colours.red, Colours.green > (<Colours.red: 1>, <Colours.green: 999>) > > so I'm not really sure what you want or how you are doing it. Can we > pretend you are reporting a bug, and ask what did you do, what did you > expect, and what happened instead? > > One can work around that by writing the code to make > > use of the name > > property after installation, but why should we force the developer to > > write code in an awkward manner when we could simply make the name > > available to the `__new__ method. > > Whose __new__ method? > [...] > > The idea that comes to mind is to pass a > > context object argument to > > __new__ with name and names attributes. To preserve > > backward > > compatibility, there could be have a class attribute named something > > like _use_context_ (False by default) to enable or disable > > passing > > that parameter. > > That sounds convoluted, complicated and confusing. Are there existing > examples where we do that? > I would think if we need an backwards-incompatible breaking change, > there are three better ways: > > a subclass of Enum that does what you want; > > following a period of deprecation, have a flag-day change to the new > behaviour (3.9 is probably too soon, but 3.10 might be possible); > > a __future__ import (although that generally only applies to syntax. > > > especially the first.
Per the `AutoName` example at https://docs.python.org/3/library/enum.html#using-automatic-values, one can easily use `_generate_next_value_` to derive a member's value from its name, but that is only invoked when the object's value is an instance of `auto()`, so if you want to give an enum member an explicit value _and_ have an attribute such as `label` derived from its name, that's a hard nut to crack. An example usage of what I'm suggesting would be something like… class ChoiceEnum(Enum): _use_context_ = True def __new__(cls, value, context): obj = object.__new__(cls) obj._value_ = value obj.label = context.name.capitalize() class Color(ChoiceEnum): SMALL = 'S' MEDIUM = 'M' LARGE = 'L' print(Color.SMALL.label) # Prints 'Small' _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/34WVVUNN7LMF2HT3ILUA3Q2AL2M4JJMK/ Code of Conduct: http://python.org/psf/codeofconduct/
