On 4/10/2014 2:52 PM, John Ladasky wrote:
Thanks to both Ethan and Steven for their replies.
Steven: I was trying to use the interpreter and wasn't getting results that I
understood -- because I didn't know that __getslice__ was simply gone in Python
3. I implemented a __getslice__ method in my subclass that never got called.
Ethan: I saw that slice objects were being sent to __getitem__, but that
confused me as I thought that its purpose, as implied by the method name, was
to return a SINGLE item.
A slice is a single sequence object. Sequences can result from any of
index lookup, key lookup, or slicings.
The backstory is that slicing originally supported only start and stop
positions. The 3 __xyzslice__ had separate start and stop parameters
instead of the 1 index/key parameter of __xyzitem__. Strides and the
slice class were introduced for the benefit of numerical python. When
they were 'mainstreamed' into regular python, the __xyzslice__ methods
were deprecated (in 2.0) as a single slice object can just as well be
passed to __xyzitem__.
--
Terry Jan Reedy
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