Rationale behind the deprecation of __getslice__?

[Fernando Perez]

Steven Bethard wrote:

> Fernando Perez wrote:
>> I was wondering if someone can help me understand why __getslice__ has been
>> deprecated, yet it remains necessary to implement it for simple slices
>> (i:j), while __getitem__ gets called for extended slices (i:j:k).
> 
> I don't think this is true -- everything goes to __getitem__:
> 
>  >>> class C(object):
> ...     def __getitem__(self, *args, **kwds):
> ...         print args, kwds
> ...
>  >>> c = C()
>  >>> c[1]
> (1,) {}
>  >>> c[1:2]
> (slice(1, 2, None),) {}
>  >>> c[1:2:-1]
> (slice(1, 2, -1),) {}

Not if you subclass builtin types like list:

In [6]: class mylist(list):
   ...:     def __getitem__(self,*args,**kwds):
   ...:         print 'mylist getitem'
   ...:         print args,kwds
   ...:

In [7]: a=mylist()

In [8]: a[1]
mylist getitem
(1,) {}

In [9]: a[1:2]
Out[9]: []

In [10]: a[1:2:3]
mylist getitem
(slice(1, 2, 3),) {}

I did this testing, which is what forced me to implement __getslice__
separately in my little example, to satisfy calls with simple i:j slices.

Best,

f