At 06:33 PM 3/15/2008 -0500, Michael Urman wrote: > > > I'm not sure how to solve this except by adopting a different syntax > > > for the multiple-yield. Perhaps > > > > > > *yield x > > > > If there really were an inconsistency here, I would certainly not suggest > > fixing it that way, yuuueghh. > >Agreed about *yield looking yucky. In a previous thread somewhere >around http://mail.python.org/pipermail/python-dev/2006-January/059955.html >a construct like "yield from x" was offered. It certainly helps >clarify the difference between iteratively yielding the values from >another iterator and yielding the values of an iterator as a tuple. >While parsing rules do differentiate, I don't find the behavior >obvious, and expect the differences between > yield *x; yield *x(); yield *x,; yield (*x,); and yield *(x,) >would become one of python's warts in a few years, if adopted.
After following this thread for a bit, I think it's a wart already. :) The potential for confusion with the other *assign target idea is too high. I don't have a problem with "item for *item,val in blah", but "*item for item in blah" makes my head hurt. Why not just say "i2 for i1 in blah for i2 in i1"? Yes, it's a bit more verbose, but not frequent enough to justify the *, and you can tell what's going on by textually transposing to the nested for loops. Plus, it works for any depth. What are you going to do if it's triple-nested? Use **? What about ***? Where does it end? So I think "yield *" and "*item for item in..." are broken for the same reason. In the function call use case, and in simple assignment, it is treated as a literal quasi-textual expansion. However, such an expansion in the yield case would yield a tuple, and the literal expansion in the comprehension case would make no sense. (If done by true textual substitution, it would have to be a syntax error.) And I think that a quasi-textual substitution is the right mental model for * expressions, as it's simple to explain and easy to reason out what happens. _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
