[Python-Dev] slice subscripts for sequences and mappings (original) (raw)

Guido van Rossum guido at python.org
Sat Mar 3 18:58:59 CET 2012

On Sat, Mar 3, 2012 at 4:20 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:

I'd expect slice subscripts to be part of the sequence interface, and yet they are not. In fact, they are part of the mapping interface. For example, the list object has its slice get/set methods assigned to a PyMappingMethods struct. So does a bytes object, and pretty much every other object that wants to support subscripts. It comes from: http://hg.python.org/cpython/rev/245224d1b8c9 http://bugs.python.org/issue400998 Written by Michael Hudson and reviewed by Guido. I wonder why this patch chose to add mapping protocol support to tuples and lists, rather than add a tp slot for extended slicing.

That's long ago... IIRC it was for binary compatibility -- I didn't want to add an extra slot to the sq struct because it would require recompilation of 3rd party extensions. At the time that was an important concern.

-- --Guido van Rossum (python.org/~guido)

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