On Thu, 2 Jul 2020 at 00:04, Elliott Chen <elliottchen2...@gmail.com> wrote: > > I saw in the PEP that "Allow more flexible assignment targets instead" was > rejected, but I actually think it's a good idea. The current PEP means there > will be two different, subtly incompatible ways to destructure objects (match > statement and iterable unpacking). The reasoning given was that most cases > involve an if-statement, but there's no reason we can't have both flexible > assignment targets and a match statement. I think unifying the concepts will > make the language more consistent and easy to learn. > > I also think destructuring an object with only one possible pattern can be > very useful, without the boilerplate to set up an entire match suite and > manually raise an exception. This will make the variable assignment statement > much more powerful. I don't see a good reason to arbitrarily restrict > variable assignment to only allow sequence patterns. This might not be a good > idea, but it can even potentially be used as an assert statement, like this: > > def __init__(self, version, name, point): > self.version = 1 | 2 | 3 = type # assert that "version" is between 1 > and 3 > self.name = str() = string # assert that "name" is the correct type > Point(0, self.y) = point # assert that "point" is on the y-axis > > The constant value pattern would have to be changed to something else, like > "@constant", and even though that's also rejected, I think the benefits > outweigh the costs here. The special treatment of "_" would have to go too, > but there's no reason it can't be used as a wildcard by convention anyway, > similar to how it can already be used in for loops. I don't see any benefit > in treating it specially. Or the question mark can be the wildcard instead.
Exactly! The wildcard spelling idea I suggested in the other thread was that "?" could become a general constraint prefix used to introduce non-literal and non-keyword constraints. I was thinking purely in terms of destructuring and not in terms of data validation, but you're right that multiple assignments would allow for "multi-capture" (albeit with the usual caveats on iterable consumption). (I think match/case is fine as the spelling for the multi-target dispatch case, though) Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/LOLDPPKHE6L75WW2FNEQHONNZK2LM6NI/ Code of Conduct: http://python.org/psf/codeofconduct/
