[Python-ideas] return value of yield expressions

H. Krishnan hetchkay at gmail.com
Tue Sep 13 19:21:22 CEST 2011

> > (a1, a2, a3 = 3, *args, **kwds) = (yield <expr>)
> What on earth is this syntax supposed to mean? Never mind that there's
> a yield on the RHS; it is just a parenthesized expression so it could
> could be any other function. What on earth do you expect to happen
> with the syntax on the left, i.e. with the part

> (a1, a2, a3 = 3, *args, **kwds) = ........whatever........
> As I said "forgeting the backward compatibility issue". Suppose we use 
Jacob's syntax (for argument's sake)

*(a1, a2, a3 = 3, *args, **kwds) = (yield expr)

and with g.send(*a, **k) being called, a1, a2, a3, args, kwds can be 
inferred using the same semantics that is used to decipher a1, a2, a3, args, 
kwds in a call to the following function with *a and **k as arguments:
def func(a1, a2, a3 = 3, *args, **kwds):

That (yield expr) can be used in expressions does not (I feel) affect this 
(particularly if we go with Jacob's suggestion of this being a general 
unpacking option), just in the same way that "a, b, *args, c = <tuple>" does 
not affect using tuples in expressions. But after reading your comment in 
another thread about those who don't know how python works should keep 
quiet, I guess it is best if I end this here :-)

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