Here's a few words on whether we should allow and whether we can forbid: >>> 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