[Python-Dev] Set data type

[David Ascher]

Ka-Ping Yee, on sets:

I think you forgot one behavior:

      >>> t.append('Spam!')
      >>> t.append('Spam!')
      KeyError: set already contains value 'Spam!'

no?  FWIW, I don't like the use of the word 'append', which to me implies a
serial order.  I'd use 'add', but that's a nit.

>     2.  How do sets sort?
[..]
>         a.  The answer is the same as whatever answer we get when
>             Python supports rich comparisons and instances can have
>             partial orderings too.
[..]
>         (Side note: Do we achieve a. just by divorcing __cmp__ from
>         >, >=, etc.?

I think we hashed (pun!) all of this out a couple of years ago in one of
your hibernation periods =).  I'll try to find the deja thread on the topic.

>         ((Side side side note: in E, Mark Miller also ran into the
>         problem of spelling different kinds of "equals"es.  For
>         object identity we have "is", for content comparison we
>         have "==".  If we need a new operator for magnitude equality
>         i suggest "<=>", as used in E.))

Isn't magnitude equality currently spelled len(a) == len(b)?

> Well, it may be a lot of words, but it's not much good unless you
> are going to use it in practice.  I think i would have good use for
> it, but i would like to hear your opinions.  Would you use such a
> thing?

I use some of the features of such a thing now by making up dictionaries
with None as values for all the keys.

I have no strong feeling re: whether we need a new datatype for sets.

-david ascher