This post does point out an inconistency in Thomas's patch: def f(): yield 1, 2, 3
Yields a single three-tuple. But def f(): yield *[1, 2], 3 Yields three separate values. I think this is inconsistent, since (1, 2, 3) and (*[1, 2], 3) are equivalent, and so are yield 1, 2, 3 and yield (1, 2, 3) I'm not sure how to solve this except by adopting a different syntax for the multiple-yield. Perhaps *yield x instead of yield *x ??? On Sat, Mar 15, 2008 at 4:58 PM, Terry Reedy <[EMAIL PROTECTED]> wrote: > > "Guido van Rossum" <[EMAIL PROTECTED]> wrote in message > news:[EMAIL PROTECTED] > > | Thomas Wouters suggests some new syntax: > > I see this as two suggestions: > 1. Complete the extension of the validity of *expression syntax from > function call/definition to expression/assignment. > 2. Give *expression a related meaning in yield statements. > > > | > | http://bugs.python.org/issue2292 > | > | >>> a, b, *c = range(5) > | > | >>> *a, b, c = a, b, *c > | >>> a, b, c > | ([0, 1, 2], 3, 4) > | >>> [ *a, b, c ] > | [0, 1, 2, 3, 4] > > I understand 'f(*a)' to mean 'execute the expression as if the items of > iterable a has been written literally in the code (with 'as if' > optimizations allowed for special cases). The above follow the same rule. > +1 > A tutorial written for Py3 without regard to history should then introduce > *expressions in examples like the above first, and only later the usage for > functions, as if things had been this way all along. > > > | >>> L = [ a, (3, 4), {5}, {6: None}, (i for i in range(7, 10)) ] > | >>> [ *item for item in L ] > | [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] > > Since above will become equivalent to list(gen_exp), I see this as being > tied to yield *exp. > > > | Also, yielding everything from an iterator: > | > | >>> def flatten(iterables): > | ... for it in iterables: > | ... yield *it > > Following the general rule above for *exp, that would be the same as yield > tuple(it). But that is nearly useless, whereas the the implicit inner for > loop meaning is quite useful, with, perhaps, a speedup over an explicit > inner loop. Since yield is already pretty magical,a bit more might not > hurt. > > But, ... what do you do with > yield *a,b,c # a,b,c as above? > Yield a 5-tuple? That would clash badly with 'yield *a' not yielding a > 3-tuple. > Raise an exception? That establishes/requires a new grammatical > category -- yield_expression. But I would see this as preferable to the > clash. > > Terry Jan Reedy > > > > > _______________________________________________ > 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/guido%40python.org > -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ 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
