The very common use case for creating slice objects is in Pandas and similar libraries. Xarray certainly, or Blaze, to a lesser extent NumPy.
That said, it's very easy to define a suitable __getitem__, as Guido shows. It's really a question simply of whether that object should be named 'slice' or something else.
On Nov 12, 2016 5:08 PM, "Guido van Rossum" firstname.lastname@example.org wrote:
On Sat, Nov 12, 2016 at 11:41 AM, Ivan Levkivskyi email@example.com wrote:
On 12 November 2016 at 20:27, David Mertz firstname.lastname@example.org wrote:
I thought of the use of `.__getitem__()` in metaclasses in the typing module. I feel like this use is more natural and more useful than that. Should we someday need a slice generic type for PEP 484, the spelling would naturally be `Slice[T]` instead, in my mind. But `slice[1:10,2]` should be a constructor for a concrete slice object.
Slice[T] vs slice[::-1] is coherent with what we have now for List[T] vs list, etc.
Not really. We have List[T] but list[x] is invalid -- it doesn't have a different meaning (it's list instances that support indexing). And in fact the distinction between List and list is intentionally minimal -- List is simply what list wants to become when it grows up. :-)
Honestly I think the use case of wanting to create a slice object is rare enough that we can continue to write slice(x, y, z). If you really find yourself wanting something shorter, I believe in the past it's been pointed out that you could create a helper, e.g. like this:
class S: def __getitem__(self, x): return x s = S()
a = s[:():]
-- --Guido van Rossum (python.org/~guido)