On Wed, Aug 26, 2020 at 9:39 PM Greg Ewing <greg.ew...@canterbury.ac.nz>
wrote:
> If we use a new set of dunders, the signature of the one for
> setting could be
>
> def __setindex__(self, value, *args, **kwds)
>
> which is not completely unsurprising, but plays better with
> an arbitrary number of positional indexes.
>
> --
> Greg
>
On Wed, Aug 26, 2020 at 9:34 PM Greg Ewing <greg.ew...@canterbury.ac.nz>
wrote:
> On 27/08/20 4:32 am, Ricky Teachey wrote:
>
> > class Q:
> > def __subscript__(self, method_name, *args, **kwargs):
> > return getattr(self, method_name)(*args, **kwargs)
> > def __getitem__(self, *args, **kwargs): ...
> > # Note that I have made the RHS value the first argument in
> __setitem__
> > def __setitem__(self, value, *args, **kwargs): ...
> > def __delitem__(self, *args, **kwargs): ...
>
> This seems like a very convoluted way of going about it as
> opposed to just adding a new full set of dunders. And I don't
> see how it actually provides any more flexibility.
>
> --
> Greg
That version of the idea I gave isn't great, I don't disagree. It wasn't
really intended to be the proposed dunder function.... just the quickest
way I could think of to write it up to attempt to illustrate to Steve in
the bit below:
> With the proposal, the language would support any function desired to turn
> > the "stuff" inside a subscripting operation into the item dunder calls.
>
> I'm sorry, I don't understand that sentence.
>
I think the argument for providing a SINGLE new dunder, rather than three,
could be that you don't have two sets of dunders that do the same thing,
just with different signatures. The purpose of a new single dunder should
simply be to translate the contents of the subscript operator to the
existing dunders.
The thing I am struggling with is how would it RETURN that translation...?
In my slapdash implementation I just CALLED them, but that seems less than
ideal.
I supposed it could do it by returning a tuple and a dict, like this:
def __key_or_index_translator__(self, pos1, *, x) -> Tuple[Tuple[Any],
Dict[str, Any]]:
"""I only allow subscripting like this:
>>> obj[1, x=2]
"""
return (pos1,), dict(x=x)
The return value then in turn gets unpacked for each of the existing item
dunders:
obj.__getitem__(*(pos1,), **dict(x=x))
obj.__setitem__(value, *(pos1,), **dict(x=x))
obj.__delitem__(*(pos1,), **dict(x=x))
Now:
class C:
__key_or_index_translator__ = __key_or_index_translator__
def __getitem__(self, *args, **kwargs): ...
def __setitem__(self, value, *args, **kwargs): ...
def __delitem__(self, *args, **kwargs): ...
>>> C()[1, 2, x=1, y=2]
TypeError
---
Ricky.
"I've never met a Kentucky man who wasn't either thinking about going home
or actually going home." - Happy Chandler
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