[Python-Dev] PEP 572: Now with 25% less reference implementation! (original) (raw)

Guido van Rossum guido at python.org
Fri Apr 20 11:50:09 EDT 2018

Maybe annotations should get a brief mention in the Rejected Ideas section, with your explanation here added. (And maybe my response.)

On Thu, Apr 19, 2018 at 11:31 PM, Chris Angelico <rosuav at gmail.com> wrote:

On Fri, Apr 20, 2018 at 2:45 PM, Dmitry Malinovsky <damalinov at gmail.com> wrote: > Hello Chris, and thank you for working on this PEP! > > What do you think about using variable type hints with this syntax? > I tried to search through python-dev and couldn't find a single post > discussing that question. > If I missed it somehow, could you please include its conclusions into the PEP?

I'm ignoring them for the sake of the PEP, because it'd complicate the grammar for little benefit. If someone wants to add an enhancement later, that's fine; but the proposal can stand without it, and with it, it'll make for even more noise in a line full of colons. > For instance, as I understand now the parser will fail on this snippet: > > while data: bytes := stream.read(): > print("Received data:", data) > > Do brackets help? > > while (data: bytes := stream.read()): > print("Received data:", data) > > IIUC, in 3.7 It is invalid syntax to specify a type hint for a for loop item; > should brackets help? Currently they don't: > > Python 3.7.0b3+ (heads/3.7:7dcfd6c, Mar 30 2018, 21:30:34) > [Clang 9.0.0 (clang-900.0.39.2)] on darwin > Type "help", "copyright", "credits" or "license" for more information. > >>> for (x: int) in [1,2,3]: > File "", line 1 > for (x: int) in [1,2,3]: > ^ > SyntaxError: invalid syntax And that's another good reason not to bother, at least for now. I'm not sure whether you can use a Py2-style type hint comment on a for loop, but if so, you should also be able to do it on a while loop or anything. Or, of course, you can just annotate the variable before the loop, if you want to. ChrisA

Python-Dev mailing list Python-Dev at python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/ guido%40python.org

-- --Guido van Rossum (python.org/~guido) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180420/3bcf2a47/attachment.html>

More information about the Python-Dev mailing list