Message 403594 - Python tracker

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Author	gvanrossum
Recipients	gvanrossum, joperez, kj, serhiy.storchaka
Date	2021-10-10.15:16:50
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<CAP7+vJKkOTeh=mEaPbOdC6smG+HOxmDpywVQU-egxP5fjKee1Q@mail.gmail.com>
In-reply-to	<1633852223.45.0.0312685952185.issue45418@roundup.psfhosted.org>

Content
> If you meant to say: why is typing.Union[] allowed, but not types.UnionType[]? That is intentional. types.UnionType is only meant for builtin types. Once you union with any type from typing, it will convert to a typing.Union. But why? Just so types.UnionType (if it has a typevar) doesn’t have to support subscriptions? Even if this saves us now, I agree with OP that it ought to allow it, so we can deprecate typing.Union properly. And e.g. dict[str, T] works. -- --Guido (mobile)

> If you meant to say: why is typing.Union[] allowed, but not
types.UnionType[]? That is intentional. types.UnionType is only meant for
builtin types. Once you union with *any* type from typing, it will convert
to a typing.Union.

But why? Just so types.UnionType (if it has a typevar) doesn’t have to
support subscriptions? Even if this saves us now, I agree with OP that it
ought to allow it, so we can deprecate typing.Union properly. And e.g.
dict[str, T] works.
-- 
--Guido (mobile)

History
Date	User	Action	Args
2021-10-10 15:16:50	gvanrossum	set	recipients: + gvanrossum, serhiy.storchaka, joperez, kj
2021-10-10 15:16:50	gvanrossum	link	issue45418 messages
2021-10-10 15:16:50	gvanrossum	create