[Python-Dev] PEP 526 ready for review: Syntax for Variable and Attribute Annotations (original) (raw)

Guido van Rossum guido at python.org
Wed Aug 31 01:40:57 EDT 2016

On Tuesday, August 30, 2016, Nick Coghlan <ncoghlan at gmail.com> wrote:

On 31 August 2016 at 13:37, Jack Diederich <jackdied at gmail.com_ _javascript:;> wrote: > On Tue, Aug 30, 2016 at 11:03 PM, Guido van Rossum <guido at python.org_ _javascript:;> wrote: >> But myfunc.annotations already exists -- PEP 3107 puts the >> signature annotations there. The problem with coannotations is that >> annotations are evaluated (they can be quite complex expressions, e.g. >> Optional[Tuple[int, int, somemod.SomeClass]]), while covarnames is >> just a list of strings. And code objects must be immutable. The issue >> with rejecting duplicate annotations so sternly is the same as for the >> previous bullet. >> > > If we disallow re-assignment of types as a syntax error then the conflict > with myfunc.annotations goes away for vars that share a name with the > function arguments. The fact that variables with types can't be known until > the function body executes a particular line is .. I'm not sure how to deal > with that. For modules and classes you can assert that the body at the top > indent level has been executed. For functions you can only assert that it > has been parsed. So myfunc.annotations could say that the type has a > definition but only later know what the definition is.

What if we included local variable annotations in func.annotations as cells, like the entries in func.closure? We could also use that as a micro-optimisation technique: once the type annotation cell is populated, CPython would just use it, rather than re-evaluating the local variable type annotation expression every time the function is called.

But what runtime use have the annotations on locals? They are not part of any inspectable interface. I don't want to spend any effort on them at runtime. (Just the bit that they are treated as locals.)

--Guido

-- --Guido (mobile) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20160830/f957883b/attachment.html>

More information about the Python-Dev mailing list