[Python-Dev] Extending tuple unpacking
greg.ewing at canterbury.ac.nz
Tue Oct 11 09:39:38 CEST 2005
Guido van Rossum wrote:
> BTW, what should
> [a, b, *rest] = (1, 2, 3, 4, 5)
> do? Should it set rest to (3, 4, 5) or to [3, 4, 5]?
Whatever type is chosen, it should be the same type, always.
The rhs could be any iterable, not just a tuple or a list.
Making a special case of preserving one or two types doesn't
seem worth it to me.
> Suppose the latter. Then should we allow
> [*rest] = x
> as alternative syntax for
> rest = list(x)
That would be a consequence of that choice, yes, but so what?
There are already infinitely many ways of writing any expression.
> ? And then perhaps
> *rest = x
> should mean
> rest = tuple(x)
> Or should that be disallowed
Why bother? What harm would result from the ability to write that?
> There certainly is a need for doing the same from the end:
> *rest, a, b = (1, 2, 3, 4, 5)
I wouldn't mind at all if *rest were only allowed at the end.
There's a pragmatic reason for that if nothing else: the rhs
can be any iterable, and there's no easy way of getting "all
but the last n" items from a general iterable.
> Where does it stop?
For me, it stops with *rest only allowed at the end, and
always yielding a predictable type (which could be either tuple
or list, I don't care).
> BTW, and quite unrelated, I've always felt uncomfortable that you have to write
> f(a, b, foo=1, bar=2, *args, **kwds)
> I've always wanted to write that as
> f(a, b, *args, foo=1, bar=2, **kwds)
Yes, I'd like that too, with the additional meaning that
foo and bar can only be specified by keyword, not by
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