[Python-ideas] a set of enum.Enum values rather than the construction of bit-sets as the "norm"?

Steven D'Aprano steve at pearwood.info
Fri Dec 29 23:25:31 EST 2017

On Sat, Dec 30, 2017 at 02:56:46AM +1100, Chris Angelico wrote:
> On Sat, Dec 30, 2017 at 2:38 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> > The lack of support for the `in` operator is a major difference, but
> > there's also `len` (equivalent to "count the one bits"), superset
> > and subset testing, various in-place mutator methods, etc. Java has a
> > BitSet class, and you can see the typical sorts of operations
> > commonly required:
> >
> > https://docs.oracle.com/javase/8/docs/api/java/util/BitSet.html
> Okay. A subclass of int could easily add a few more. Counting the 1
> bits isn't difficult; superset and subset testing are actually the
> same as 'contains' but with more than one bit at a time. (In fact,
> checking if a set contains a subset is *easier* with ints than with
> actual sets!) Are in-place mutators that big a deal? I'm sure there
> are sets in languages with no mutables.

We seem to be talking at cross-purposes.

Obviously we can and do already use ints as if they were set-like data 
structures. For example, the re module already does so. If you want to 
call that a kind of "bit set", I'm okay with that, but Wikipedia 
suggests that "bit array" is the canonical name:

    "bit array (also known as bit map , bit set, bit string, or
    bit vector)"


The obvious reason why is that sets are unordered but arrays of bits are 
not: 0b1000 is not the same "set" as 0b0010.

However, the point I was making was that ints don't provide the same 
interface as sets. I don't deny that you can use an int to provide 
set-like functionality, or that with sufficient effort you could 
subclass int to do so, but what you cannot do is seemlessly interchange 
an int for a set and visa versa and expect the code to work without 
modification. Even if the function is limited to using the set-like 

I think I have beaten this dead horse enough. This was a minor point 
about the terminology being used, so I think we're now just waiting on 
Paddy to clarify what his proposal means in concrete terms.


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