C Anthony Risinger wrote:
`a, b, ...` to me says "pull out a and b and throw away the rest"...
> The mere presence of more
characters (...) implies something else will *happen* to the remaining items, not that they will be skipped.
It seems that many people think about unpacking rather differently from the way I do. I think the difference is procedural vs. declarative. To my way of thinking, something like a, b, c = x is a pattern-matching operation. It's declaring that x is a sequence of three things, and giving names to those things. It's not saying to *do* anything to x. With that interpretation, a, b, ... = x is declaring that x is a sequence of at least two items, and giving names to the first two. The ellipsis just means that there could be more items, but we don't want to give them names. On the other hand, some people seem to be interpreting the word "unpack" as in "unpack a suitcase", i.e. the suitcase is empty afterwards. But unpacking has never meant that in Python! If it did, then x = [1, 2, 3] a, b, c = x would leave x == [] afterwards. The only case where unpacking behaves like that is when the rhs is an iterator rather than a sequence, in which case a side effect is unavoidable. The question then is what the side effect should be. I would argue that, since the side effect is something that's not really wanted, it should be as *small* as possible. By that argument, a, b, ... = some_iterator should do as *little* as possible to fulfill what's being asked, i.e. give names to the first two items produced by the rhs. Consuming those two items is unavoidable, but there's no need to consume any more. As for the "extra syntax", we only need it because we've defined the existing unpacking syntax to imply verifying that the rhs has exactly the same length as the pattern. We now want to express patterns which don't impose a length constraint, so we need to write them some other way. -- Greg _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
