Hi Ricky
Thank you for your very helpful comment, which Paul has usefully amplified.
You wrote:
This is confusing to me because `my_mapping[1,2,3]` is already valid syntax
> equivalent to `my_mapping.__setitem__(my_mapping, (1,2,3))`. Wouldn't a
> change to translate the tuple into this K object lead to big problems for a
> lot of existing code...?
Yes it would, if we don't take care to maintain backwards compatibility. At
present we have:
>>> class Dummy:
... def __getitem__(self, *argv, **kwargs):
... return argv, kwargs
>>> d = Dummy()
>>> d[1, 2, 3]
(((1, 2, 3),), {})
This behaviour must be preserved. Only when the new syntax is used
should d.__getitem__ get an instance of the new class K. Otherwise, it
should as before get a tuple, exactly as before. (Therefore, it might be
good that K(1, 2, 3) returns the tuple (1, 2, 3), rather than an instance
of K. As I recall, this can be done by using a suitable K.__new__ method.)
And this would include the use of colon to obtain slices.:
>>> d[0:1,2:3,4:5]
(((slice(0, 1, None), slice(2, 3, None), slice(4, 5, None)),), {})
This solution to backwards compatibility is another reason for using a
K.adjust_get decorator, when defining the __getitem__ for a map that relies
on the new syntax. That way, if the programmer wants the new feature, the
appropriate marshalling of positional (and keyword) arguments is done by a
dedicated piece of code.
I hope this helps, and thank you again for your query (and Paul for his
constructive critical interest).
--
Jonathan
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