[Python-Dev] Re: stdlib Flag Enums and the "no value" member

2021年4月29日 10:37:33 -0700

On Thu, Apr 29, 2021 at 1:20 PM Ethan Furman <[email protected]> wrote:
> An excerpt from bpo-31369: re.RegexFlag and `__all__`
>
> GvR:
> ----
> > One thing I discovered when developing this example: there doesn't seem
> to be a flag to
> > represent 0 (zero), i.e. "no flags". And foo(0) is a type error (even
> though it works
> > fine at runtime).
>
> Which raises the question: Do we want to have a standard name for stdlib
> Flags when no flags are set?
>
> What should we call it?
>
> - NONE
>
> - ZERO
>
> - EMPTY
>
> - ???
>
If you want a flag to represent no flags set, it takes one line to write it
yourself, as in this example I copied verbatim from the docs:
>>> class Color(Flag):
... BLACK = 0
... RED = auto()
... BLUE = auto()
... GREEN = auto()
...
>>> Color.BLACK
<Color.BLACK: 0>
>>> bool(Color.BLACK)
False
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