>
>
> You can now use `{*()}` as a syntax for empty set.
>
> I saw that in the ast module and think it's clever, mainly in a good way.
I don't think it is the same as having dedicated syntax for the empty set
partly because I think it needs to be taught. I don't think a new
pythonista would turn to empty tuple unpacking to get the empty set, where
I do think that either set() or {,} would be natural, at least after some
trial and exceptions. It also doesn't give quite the optimization as {,}.
$ def comma_set():
> return {,}
>
$ dis.dis(comma_set)
2 0 BUILD_SET 0
2 RETURN_VALUE
$ def unpack_set():
> return {*()}
>
$ dis.dis(unpack_set)
2 0 BUILD_SET 0
2 LOAD_CONST 1 (())
4 SET_UPDATE 1
6 RETURN_VALUE
although it is better than recommendations I have seen for 2.7 code
$ def and_set():
> return {1} & {2}
>
$ dis.dis(and_set)
2 0 LOAD_CONST 1 (1)
2 BUILD_SET 1
4 LOAD_CONST 2 (2)
6 BUILD_SET 1
8 BINARY_AND
10 RETURN_VALUE
Part of the problem here might be the teaching; if {*()} had been talked
about since 3.0 and pointed out in documentation and tutorials I likely
would never have thought to raise this proposal. But I don't think it is
well known, and not often used. I gave examples of where in cpython set()
is used, however {*()} is only used once, as a string in ast.py; not even
set repr uses this fancy syntax but instead returns "set()" for the empty
set, even though braces are used to repr sets of any non-zero length.
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