[Python-ideas] PEP 563 and expensive backwards compatibility

[Guido van Rossum]

On Wed, Sep 13, 2017 at 11:56 AM, Jim J. Jewett <jimjjewett at gmail.com>
wrote:

> It should be possible to opt out for an entire module, and it should
> be possible to do so *without* first importing typing.
>

PEP 484 has a notation for this -- put

  # type: ignore

at the top of your file and the file won't be type-checked. (Before you
test this, mypy doesn't yet support this. But it could.)

IIUC functions and classes will still have an __annotations__ attribute
(except when it would be empty) so even with the __future__ import (or in
Python 4.0) you could still make non-standard use of annotations pretty
easily -- you'd just get a string rather than an object. (And a simple
eval() will turn the string into an object -- the PEP has a lot of extra
caution because currently the evaluation happens in the scope where the
annotation is encountered, but if you don't care about that everything's
easy.)

-- 
--Guido van Rossum (python.org/~guido)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20170913/f70a0593/attachment.html>