[Python-Dev] Slices and "==" optimization

[Guido van Rossum]

> 1. Even though you can construct slice objects in Python
>    using slice(left,right), you can't really do anything
>    with them; at least not on the standard types (Numeric's
>    arrays work with them just fine).
> 
>    Couldn't we add some functionality which makes them
>    compatible to lists and tuples (and perhaps even in a
>    generic way for other sequences using PySequence_GetItem())
>    too ?
> 
>    I thinking of extending the __getitem__ hook to accept
>    slice objects. You could then maintain slices to an
>    object in say a list and apply them to the underlying text
>    as needed, e.g.
> 
>    s = slice(1,4)
>    l = range(10)
>    l[s] == [1, 2, 3]

I agree that this would be nice to have.  I won't have time for it
before 2.2 is out, but if you want to give it a crack, I might accept
it.

> 2. Looking through the code for '==' the optimization for
>    'a == a' seems too far down the call stack. Since interning
>    strings makes this case rather common, I'd suggest to
>    lift the optimization into the ceval loop (right along side
>    with the INT op INT optimization).

I would agree, except there's also the point of view that since types
can override __eq__ to always return false, this optimization should
not be done in a way that prevents __eq__ from overriding it.

--Guido van Rossum (home page: http://www.python.org/~guido/)