[Python-ideas] Support multiplication for sets

[Paul Moore]

On 7 October 2011 11:37, Jakob Bowyer <jkbbwr at gmail.com> wrote:
> There is that but from a math point of view the syntax a * b does make
> sence.
> Its slightly clearer and makes more sense to people from outside of a
> programming background.

I'm not sure I'd agree, even though I come from a maths background.
Explicit is better than implicit and all that...

Even if it is slightly clearer to some people, I bet there are others
(not from a mathematical background) who would be confused by it. And
in that case, itertools.product is easier to google for than "*"...)
And that's ignoring the cost of implementing, testing, documenting the
change.

Actually, just to give a flavour of the sorts of design decisions that
would need to be considered, consider this:

>>> a = set((1,2))
>>> b = set((3,4))
>>> c = set((5,6))
>>> from itertools import product
>>> def times(s1,s2):
...    return set(product(s1,s2))
...
>>> times(a,times(b,c))
{(1, (3, 6)), (2, (3, 5)), (2, (4, 5)), (1, (4, 6)), (1, (4, 5)), (2,
(3, 6)), (2, (4, 6)), (1, (3, 5))}
>>> times(times(a,b),c)
{((2, 4), 6), ((1, 4), 5), ((1, 4), 6), ((2, 3), 6), ((1, 3), 6), ((2,
3), 5), ((2, 4), 5), ((1, 3), 5)}
>>>

So your multiplication isn't commutative (the types of the elements in
the 2 expressions above are different). That doesn't seem intuitive -
so maybe a*b*c should be a set of 3-tuples. But how would that work?
The problem very quickly becomes a lot larger than you first assume.

Operator overloading is used much more sparingly in Python than in,
say, C++. It's as much a language style issue as anything else.

Sorry, but I still don't see enough benefit to justify this.

Paul.