[Python-3000] Set literals (original) (raw)

Georg Brandl g.brandl at gmx.net
Mon Aug 28 21:52:53 CEST 2006

Guido van Rossum wrote:

> Georg, can you do something about repr() of an empty set? This > currently produces "{}" while it should produce "set()".

Right, forgot about that case. I'll correct that now. (Grr, I even mindlessly changed the unittest that would have caught it) Checkin?

Done. It now also renders repr(frozenset()) as "frozenset()", which should cause no problems though.

In the meantime, I played around with the peepholer and tried to copy the "for x in tupleorlist" optimization for sets. Results are in SF patch #1548082.

>> Set comprehensions are not implemented. > > ETA? There are some points I'd like to have clarified first: * would it be wise to have some general listcomp <-> genexp cleanup first? This starts with the grammar, which currently is slightly different (see Grammar:79), and it looks like there's quite a lot of (almost) duplicated code in ast.c and compile.c too. I expec this cleanup to be quite a bit of work since the semantics are seriously different. ([...] uses the surrounding scope for the loop control variables.)

I didn't say that I wanted to champion that cleanup ;)

However you might be able to just cleanup the grammar so they are identical, that would be simpler I suspect.

Looking at the grammar, there's only testlist_safe left to kill, in favor of or_test like in generator expressions. The old_ rules are still needed.

Hm. Is the precedence in

x = lambda: 1 if 0 else 2

really obvious?

* list comprehensions are special-cased because of the LISTAPPEND opcode. If there isn't going to be a special-cased SETADD, it's probably the easiest thing to transform {x for x in a} into set(x for x in a) in the AST step, with "set" of course always being the builtin set. Right. That might actually become a prototype for how to the list translation as well.

Would this need a new opcode, or should generators be special-cased by BUILD_SET?

Which doesn't seem like a good idea because it means that {(x for x in iterable)} == {x for x in iterable}

Georg

More information about the Python-3000 mailing list