This is a continuation of my previous post. I wrote:
Here's an example of how the new dunder might work in practice.
>
> class A:
> __keyfn__ = None
> def __setitem__(self, val, x=0, y=0, z=0):
> print((val, x, y, z))
>
> >>> a = A()
> >>> a[1, z=2] = 'hello'
> ('hello', 1, 0, 2)
>
To continue, suppose that True is the default value for __keyfn__.
Consider now
class C:
__keyfn__ = True
def __setitem__(self, *argv, **kwargs):
print(f'argv={argv} | kwargs={kwargs}')
Here's one option for what should happen.
>>> c = C()
>>> c[1] = 'val'
argv=(1, 'val') | kwargs={}
>>> c[1, 2] = 'val'
argv=((1, 2), 'val') | kwargs={}
>>> c[a=1] = 'val'
TypeError: __keyfn__ got unexpected keyword argument 'a'
By the way, I've not tested this code.
In short, the present behaviour continues, except that that the compile
time error
>>> c[a=1] = 'val
SyntaxError: invalid syntax
is replaced by the run-time error
>>> c[a=1] = 'val'
TypeError: __keyfn__ got unexpected keyword argument 'a'
Some of us want
>>> d = dict()
>>> d[a=1] = 'val'
to raise an exception. I've just described how having True as the default
value for __keyfunc__ allows that to happen, should the Python community so
decide.
I hope this message helps.
--
Jonathan
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