On Sat, Aug 29, 2020, at 10:12, Ricky Teachey wrote:
> If we add kwargs to the subscript operator, we'll be able to add new
> required or optional names to item dunder signatures and supply named
> arguments :
>
> def __getitem__(self, key, x, y): ...
>
> q[x=1, y=2]
>
> But if we want to have the same behavior without supporting function
> style syntax, we will have to write code like this:
>
> MISSING = object()
>
> def __getitem__(self, key, x=MISSING, y=MISSING):
> if x is MISSING and y is MISSING::
> x, y = key
> if x is missing:
> x, = key
> if y is MISSING:
> y, = key
[side note: I don't believe the behavior suggested by this last "if y is
MISSING:" clause is supported by your proposal either. It's certainly not
supported by function calls. Are you suggesting q[x=1, 2], or q[2, x=1] to be
equivalent to y=2?]
def _getitem(self, x=..., y=...):
...
def __getitem__(self, arg, /, **kwargs):
if isinstance(arg, tuple): return self._getitem(*arg, **kwargs)
else: return self._getitem(arg, **kwargs)
or, as a more compact if slightly less efficient version
def __getitem__(self, arg, /, **kwargs):
return self._getitem(*(arg if isinstance(arg, tuple) else (arg,)), **kwargs)
This is only a few lines [which would have to be duplicated for set/del, but
still], you're free to implement it on your own if necessary for your use case.
My code assumes that no positional arguments results in an empty tuple being
passed - it would be slightly more complex but still manageable if something
else is used instead.
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