[Python-ideas] IntFlags

[Eugene Toder]

Maybe even call it BitSet, and model the interface based on frozenset,
except that every element is also a set of one. The operations will be:
X | Y -- union
X & Y -- intersection
X ^ Y -- symmetric difference
X - Y -- difference
X in Y == (X & Y) == X
len(X) -- number of set bits
bool(X) -- any bits set
isdisjoint, issubset, issuperset == not X & Y, not X - Y, not Y - X
(Note no negation.)

Eugene

On Thu, Mar 5, 2015 at 11:15 AM, Luciano Ramalho <luciano at ramalho.org>
wrote:

> I like the IntFlags concept, as long as it's clearly separated from
> IntEnum -- it seems that's the consensus now.
>
> I don't like the name IntFlags: BitFlags makes more sense to me, since
> the key feature is supporting bitwise operators.
>
> Calling it BitFlags has the additional advantage of making it very
> clear that it's not closely related to IntEnum.
>
> Best,
>
> Luciano
>
> On Tue, Mar 3, 2015 at 12:52 PM, Serhiy Storchaka <storchaka at gmail.com>
> wrote:
> > Enum and IntEnum classes allow constants to have nice str() and repr()
> > representations.
> >
> >>>> socket.AF_INET
> > <AddressFamily.AF_INET: 2>
> >>>> socket.socket()
> > <socket.socket fd=3, family=AddressFamily.AF_INET,
> > type=SocketKind.SOCK_STREAM, proto=0, laddr=('0.0.0.0', 0)>
> >
> > But when integer constants are flags that should be ORed, IntEnum doesn't
> > help, because the result of bitwise OR of two IntEnum instances is int,
> and
> > this value can't be represented as IntEnum.
> >
> > We need new type IntFlags. It is like IntEnum, but has differences:
> >
> > 1. The value of an instance should be not limited to the set of
> predefined
> > constants. It can be a combination of predefined constants or even
> arbitrary
> > integer.
> >
> > 2. The result of "|", "&" and "~" operators for IntFlags arguments
> should be
> > an instance of the same IntFlags subclass.
> >
> > 3. It should have nice str() and repr().
> >
> >>>> print(stat.S_IROTH | stat.S_IWOTH)
> > stat.S_IROTH|stat.S_IWOTH
> >>>> stat.S_IROTH | stat.S_IWOTH
> > <StatFlags.S_IROTH|S_IWOTH: 6>
> >
> > Any thoughts?
> >
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>
>
>
> --
> Luciano Ramalho
> Twitter: @ramalhoorg
>
> Professor em: http://python.pro.br
> Twitter: @pythonprobr
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