how so? I don't see how this interferes at all unless the metaclass is trying to implement genericism itself Anthony On Fri, Sep 20, 2019, 9:48 PM Markus Unterwaditzer <markus@unterwaditzer.net> wrote:
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 <https://www.python.org/dev/peps/pep-0563/#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.
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