[snip]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__:
Not if you subclass builtin types like list:
Ahh, I didn't catch that your problem was with list. Yeah, so if a __getslice__ exists, this is used first. Unfortunately, by inheriting from list, you inherit __getslice__ from list. Another example without builtin types:
>>> class C(object): ... def __getitem__(self, x): ... print "C:getitem" ... def __getslice__(self, *args): ... print "C:getslice" ... >>> class D(C): ... def __getitem__(self, x): ... print "D:getitem" ... >>> d = D() >>> d[1] D:getitem >>> d[1:2] C:getslice >>> d[1:2:-1] D:getitem
While the D class doesn't define __getslice__, it's parent class does, so it has the same behavior you're running into. I don't see how to fix this other than overriding __getslice__ to call __getitem__ like you have.
Unfortunately, I don't think __getslice__ can be removed from list (and str and tuple) because of backwards compatibility constraints...
Steve -- http://mail.python.org/mailman/listinfo/python-list
