>>> something[]

First, in

    >>> something[x=1]

what I call the argv is empty, as it is with

    >>> something[]

If we represent an empty argv by passing the empty tuple () to __getitem__, then how are

    >>> something[(), x=1]

    >>> something[x=1]

to be distinguished from each other? Or perhaps they shouldn't be.

Next, if

    >>> something[*argv]

is allowed, then what was a syntax error becomes a run-time error. Put another way, an optimising compiler might want to raise syntax error for

   >>> something[*()]

although I think that would be wrong. Compare with

    >>> 1 if True else 1 / 0
    1

as its possible that something[*()] won't be called.

Finally, even if we forbid

   >>> something[*argv]

in order to prevent the empty key, the door is still open. We can use

    >>> something[**dict()]

to access something with the empty key (assuming ** arguments are allowed).

And one more thing. There's rightly a strong association between [] and an empty list literal. To my mind, this makes

    >>> d[]

look very odd. We're expecting something, but there's nothing there. Perhaps

   >>> d[-]

would work better for signifying an empty key. Here, '[-]' is a special syntactic token.

Aside: Consistent with this, we could use

   >>> {-}

for the empty set literal. At present the closest we can do for an empty set literal is

    >>> {0} - {0}

    set()

I hope all this helps.

-- 

Jonathan