On 4/13/07, Kyle Schalm <[EMAIL PROTECTED]> wrote:
> >> while i'm on the topic of sets, is the Set class intended to be immutable?
> >
> > No. The builtin Python set type isn't immutable, so it doesn't
> > seem sensible to make the SAGE one immutable. E.g., the
> > builtin set type has an add method:
>
> ok, but there is no add method in the SAGE Set, nor is there a remove
> method. so as it stand right now, it isn't very similar to a python set.
There should be a remove and add method. I forgot to implement them.
> > Sets in SAGE should have very similar behavior to Python sets,
> > except "be more mathematical", and of course allow for infinite
> > sets. Thus actually, regarding your previous patch, sets shouldn't
> > be allowed as dictionary keys and shouldn't have a hash method
> > at all, or have one that raises type error. If you want to use one
> > as a key, you should maybe be using a tuple instead.
>
> if Sets aren't going to be usable as dictionary keys, then i'm going to
> create a new immutable set class that can, because i really need that.
> tuples won't cut it.
I totally understand. Immutable types are really useful in practice.
> > I would not be opposed to creating an immutability flag
> > for sets, and having a "set_immutable" option (like with
> > Sequences), to create immutable sets. But those shouldn't
> > be the default.
>
> you mean something like
>
> s = Set([1,2,3],immutable=True)
>
> ? that would work for me.
Yes, exactly. Also,
s = Set([1,2,3])
then
s.set_immutable()
Definitely look at the Sequence code in structure/sequence.py
before implementing the above though.
> in any case, i think the following behaviour
>
> >>
> >> In [58]: x=[1,2,3]
> >>
> >> In [59]: s=Set(x)
> >>
> >> In [60]: x[1]=5
> >>
> >> In [61]: s
> >> Out[61]: {1, 3, 5}
>
>
> is still highly undesirable.
I agree. Removing setitem, as I think you did, is a good
idea. The python builtin set doesn't have it.
> shall i go ahead and add the immutable option, and some add and remove
> methods?
Yes. Thanks!
William
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