ANN: set-0.2 module available

[Aric Coady]

On Tuesday, May 21, 2002, at 03:15 AM, Denis S. Otkidach wrote:
> Here is another problem:
>>>> from set import set
>>>> s=set((1,3,5))
>>>> hash(s)
> 1272199707
>>>> s&=set((2,4,6))
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: set has become immutable
>
> If the set became immutable it should not be modified in-place,
> but &= operator should create new object according to ?=
> documentation.  Unfortunately, it makes this error prone "2 in 1"
> solution even more hard to debug.

I agree that's unfortunate, but I like the alternative even less.  To 
me, the fact that it will raise an error if you inadvertently use a set 
as if it's both mutable and hashable is precisely the reason why it's an 
acceptable compromise to let it act as either mutable or hashable.

If I had to give up those immutable errors, I'd rather just choose one 
(mutable) to be the default and force those who want it to be hashable 
to choose that explicitly.