Thank you Steven for the explanation. I like that the behaviors in annotation or outside it are the same. It makes sense and it’s easier to teach and learn. Maybe it’s not a good idea after all even though visually it makes sense to me as a normal python user. You guys see things differently because you are familiar with the CPython internals. > On 6 Feb 2022, at 2:32 AM, Steven D'Aprano <st...@pearwood.info> wrote: > > On Sun, Feb 06, 2022 at 02:13:59AM +0400, Abdulla Al Kathiri wrote: > >> The “|” operator is another way of doing Union[Literal[“John], None] >> which is already supported in the new versions of Python. Correct me >> if I am wrong please. Maybe the types already use __or__ and __ror__ >> to sugar coat Union? > > Type objects are objects, and their behaviour is controlled by their > metaclass, just as instances are objects and their behaviour is > controlled by their class. That means we can do this: > >>>> T = int | float >>>> type(T) > <class 'types.UnionType'> > > What we can't do is have instances behave differently according to > context. There is no way to have the `|` operator behave differently in > different contexts: > > value = 1 | 8 # return 9 > T = 1 | 8 # return Literal[1, 8] > L = [0, 1 | 8, 2] # what should | do inside a list? > arr[:1 | 8] # what about after a colon in a slice? > > >> Maybe if integers or strings or any other literal >> occurs after “:”, we could treat them slightly differently than what >> their actual __or__ and __ror__ would normally do? > > Fortunately the Steering Council has said that syntax in annotations and > syntax outside of annotations will remain the same. So any expression > that you can write in an annotation will have the same meaning if you > take it out and assign it to a named type. > > In other words, we can always refactor type hints by moving them out of > the annotation: > > x: expression = value > > T = expression > x: T = value > > And that is excellent. > > > -- > Steve > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/HF5FNOUQWFZ2442SPJUS6EDPELEMEHTD/ > Code of Conduct: http://python.org/psf/codeofconduct/
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