New submission from Fabio Zadrozny <fab...@users.sourceforge.net>: Note: A discussion related to this bug was raised on: http://mail.python.org/pipermail/python-dev/2009-March/086939.html
The following constructs are ambiguous in the Python 3.0 grammar: arglist: (argument ',')* (argument [','] |'*' test (',' argument)* [',' '**' test] |'**' test ) argument: test [comp_for] test: or_test or_test: and_test and_test: not_test not_test: 'not' not_test | comparison comparison: star_expr star_expr: ['*'] expr So, with that construct, having call(arglist) in a format: call(*test), the grammar would find it to be consumed in the argument construction (because of the star_expr) and not in the arglist in the '*' test. Python seems to be lucky in this because it seems to be getting in the correct choice, when that's not really possible from the grammar -- maybe it tries the 2nd construct before the 1st and succeeds because of that? It seems to me that this could actually be a bug in the Python grammar generator. It doesn't seem possible to disambiguate that without semantic actions later on, but the grammar could be changed to disambiguate that. I've used the constructs below in a JavaCC grammar successfully (and I think Python could use the same constructs): expr_stmt: testlist_star_expr (augassign (yield_expr|testlist) | ('=' (yield_expr|testlist_star_expr))*) testlist_star_expr: (test|star_expr) (',' test|star_expr)* [','] star_expr: '*' expr ---------- components: Interpreter Core message_count: 1.0 messages: 83395 nosy: fabioz nosy_count: 1.0 severity: normal status: open title: Python 3.0 grammar is ambiguous with the addition of star_expr type: feature request versions: Python 3.0, Python 3.1 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue5460> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com