Code that defines dunder methods on meta classes is likely already broken due to use of __getitem__ for generics. So there exists a precedent for not caring about such code.

On September 20, 2019 6:04:04 PM GMT+02:00, Anthony Sottile <asottile@umich.edu> wrote:

I'd like to see a backward compatibility concern highlighted in the PEP -- given it's possible (and likely?) that some metaclass in the wild already defines `__or__` or `__invert__` semantics

>>> class M(type):
...     def __or__(self, other): return self
...
>>> class C(metaclass=M): pass
...
>>> C | int

<class '__main__.C'>

Anthony

On Fri, Sep 20, 2019 at 7:16 AM Philippe Prados <philippe.prados@gmail.com> wrote:

The Resolving type hints at runtime says: “For code which uses annotations for other purposes, a regular eval(ann, globals, locals) call is enough to resolve the annotation.”. Without add a new operator `__or__` in type `type`, it’s not possible to resolve type hints at runtime.

>>> from __future__ import annotations >>> def foo() -> int | str: pass ... >>> eval(foo.__annotations__['return']) Traceback (most recent call last):   File "<stdin>", line 1, in <module>   File "<string>", line 1, in <module> TypeError: unsupported operand type(s) for |: 'type' and 'type'

Le ven. 20 sept. 2019 à 15:35, Sebastian Rittau <srittau@rittau.biz> a écrit :

Am 20.09.19 um 14:49 schrieb Chris Angelico:
> Both "int or str" and "str?" have the problem that they don't work
> under existing Python syntax, so they would be far greater changes.
> The definition of the "or" operator is baked into the language, but
> the "|" operator can have its semantics defined by the objects on
> either side.

"or" works with "from __future__ import annotations", which is a fine
limitation in my opinion.

  - Sebastian
_______________________________________________
Typing-sig mailing list -- typing-sig@python.org
To unsubscribe send an email to typing-sig-leave@python.org
https://mail.python.org/mailman3/lists/typing-sig.python.org/

_______________________________________________
Typing-sig mailing list -- typing-sig@python.org
To unsubscribe send an email to typing-sig-leave@python.org
https://mail.python.org/mailman3/lists/typing-sig.python.org/

_______________________________________________
Typing-sig mailing list -- typing-sig@python.org
To unsubscribe send an email to typing-sig-leave@python.org
https://mail.python.org/mailman3/lists/typing-sig.python.org/