On Sat, 25 Sept 2021 at 02:16, Chris Angelico <ros...@gmail.com> wrote:
> On Sat, Sep 25, 2021 at 11:11 AM Oscar Benjamin
> <oscar.j.benja...@gmail.com> wrote:
> >
> > On Sat, 25 Sept 2021 at 02:01, Chris Angelico <ros...@gmail.com> wrote:
> >>
> >> On Sat, Sep 25, 2021 at 10:56 AM Oscar Benjamin
> >> <oscar.j.benja...@gmail.com> wrote:
> >> >
> >> > On Sat, 25 Sept 2021 at 00:37, Greg Ewing <
> greg.ew...@canterbury.ac.nz>
> >> > wrote:
> >> > > I suppose they could be fiddled somehow to make it possible, but
> >> > > that would be turning them into special cases that break the rules.
> >> > > It would be better to provide separate functions, as was done with
> >> > > sum().
> >> > >
> >> >
> >> > A separate union function would be good. Even in a situation where all
> >> > inputs are assured to be sets the set.union method fails the base
> case:
> >> >
> >> > >>> sets = []
> >> > >>> set.union(*sets)
> >> > Traceback (most recent call last):
> >> > File "<stdin>", line 1, in <module>
> >> > TypeError: descriptor 'union' of 'set' object needs an argument
> >> >
> >> > In the case of intersection perhaps the base case should be undefined.
> >> >
> >>
> >> Rather than calling the unbound method, why not just call it on an
> >> empty set? That defines your base case as well.
> >>
> >> set().union(*sets)
> >
> >
> > That is indeed what I do but it seems unnatural compared to simply
> union(*sets). It shouldn't be necessary to create a redundant empty set
> just to compute the union of some other sets. If there was a union function
> then I don't think I would ever use the union method.
> >
>
> Maybe, but if you start with a set, then you define the base case, and
> it also is quite happy to take non-set arguments:
>
> >>> set().union([1,2,3], map(int, "234"), {3:"three",4:"four",5:"five"})
> {1, 2, 3, 4, 5}
Actually it should be union(sets) rather than union(*sets). A more
realistic example is when you need the union of sets given by something
like a generator expression so it looks like:
items = set().union(*(f(x) for x in stuff))
With a union function it should look like:
items = union(f(x) for x in stuff)
--
Oscar
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