The next release of kwkey will provide a class A with the following property.

It is that

>>> A(1, 2, a=3, b=4)[d] = 'val'

will result in

>>> d.__setitem__((1, 2), 'val', a=3, b=4)

This is precisely the same call that would result from

>>> d[1, 2, a=3, b=4] = 'val'

using the semantics that Guido currently favours.

Further, to better support exploration, the call instead will be

This will allow experiments via subclassing an existing class, for example from xarray. Using _A_setitem__ etc means that the new

>>> A(1, 2, a=3, b=4)[d] = 'val'

semantics can be implemented via the already existing

Both the commands

>>> d[SOMETHING] = 'val'
>>> A(1, 2, a=3, b=4)[d] = 'val'

can thus work on the same mapping / sequence instance d. The two implementations can peacefully co-exist.

For clarity, when available

>>> d[1, 2, a=3, b=4] = 'val'

is most likely to be better than

>>> A(1, 2, a=3, b=4)[d] = 'val'

and I introduce the A second form as a useful stopgap, until the first form is available.

A reminder. The purpose of kwkey is to provide a convenient way for people to experiment with different approaches to implementing the semantics of

>>> d[1, 2, a=3, b=4] = 'val'

and, perhaps, to provide a compatible implementation in present day Python. For fairness, I hope also to provide a class B that supports the __keyfn__ semantics.

I hope to make this release next week. Comments are welcome.

https://pypi.org/project/kwkey/ https://github.com/jfine2358/python-kwkey/issues/3

-- Jonathan