Different "look and feel" of some built-in functions

[Oscar Benjamin]

On Sat, 25 Sept 2021 at 00:37, Greg Ewing <greg.ewing at canterbury.ac.nz>
wrote:

> On 25/09/21 10:15 am, Steve Keller wrote:
> > BTW, I like how the min() and max() functions allow both ways of being
> > called.
>
> That wouldn't work for set.union and set.intersection, because as
> was pointed out, they're actually methods, so set.union(some_seq)
> is a type error:
>
>  >>> a = {1, 2}
>  >>> b = {3, 4}
>  >>> set.union([a, b])
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> TypeError: descriptor 'union' for 'set' objects doesn't apply to a
> 'list' object
>
> 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.

--
Oscar