[Python-ideas] How assignment should work with generators?

Kirill Balunov kirillbalunov at gmail.com
Mon Nov 27 07:31:38 EST 2017

> In terms of language proposals, you can't just say "don't need values
> for"; the semantics have to be EITHER "consume and discard" OR "don't
> consume". We already have a perfectly good way of spelling "consume
> and discard":
> x, y, _ = iter

You mean ( x, y, *_ = iter ) ?

Since this has to be about non-consumption of the generator/iterator,
> Ellipsis cannot be a zero-length deque. Thus this syntax would have to
> be restricted to the *last* entry, and it then means "don't check for
> more elements".

Yes, you are right to the *last* entry. (*last* depends on proposed syntax

> The proposed semantics, if I understand you correctly, are:
> try:
>     _iter = iter(it)
>     x = next(_iter)
>     y = next(_iter)
> except StopIteration:
>     raise ValueError
> # no "else" clause, we're done here

Yes, "roughly" this semantics is proposed, with some assumptions on _iter =
As I can see at the moment, these cases should behave differently:

>>> x, y = [1,2,3,4]             # must raise ValueError
>>> x, y = iter([1,2,3,4])      # should work

But at the same time, it violates current situation. So maybe, as you have
said we need special syntax. I will think about it.

> Start by perusing PEP 1, and the template in PEP 12:
> https://www.python.org/dev/peps/pep-0001/
> https://www.python.org/dev/peps/pep-0012/
> The PEP editors (myself included) are here to help you; don't hesitate
> to reach out with questions.

Thank you!

With kind regards, -gdg
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