[Python-ideas] return value of yield expressions

[H. Krishnan]

>
> Consider this example:
>
> def foo():
>     *(a, b) = yield
>
> f = foo()
> next(f)
> f.send(1, 2)  # Ok
>
> def wrapper(g):
>     r = next(g)
>     while 1:
>         args = (yield r)
>         r = g.send(args) # BOOM!
>
> f = wrapper(foo())
> next(f)
> f.send(1, 2) # BOOM!
>
>
> That wrapper works today, and does nothing (except messing up throw
> handling, but that is a different story).  With your suggested change,
> such a wrapper would break unless it was changed to use
>
>   *(*args, **kwargs) = (yield r)
>
> instead.  IOW a backwards incompatible change.
>
I still don't get it. f.send(1, 2) is not allowed now. The wrapper will 
still work for send() with single argument and so there is no backward 
compatibility issue. The wrapper itself could be updated to support multiple 
arguments to send if and when it is allowed.
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