[issue29262] Provide a way to check for *real* typing.Union instances

Change by Ivan Levkivskyi : -- resolution: -> fixed stage: patch review -> resolved status: open -> closed versions: +Python 3.8 -Python 3.6 ___ Python tracker ___

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: New changeset 4c23aff065fb28aba789a211937a2af974842110 by Ivan Levkivskyi in branch 'master': bpo-29262: Add get_origin() and get_args() introspection helpers to typing (GH-13685)

[issue29262] Provide a way to check for *real* typing.Union instances

Change by Ivan Levkivskyi : -- keywords: +patch pull_requests: +13573 stage: -> patch review pull_request: https://github.com/python/cpython/pull/13685 ___ Python tracker ___

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: The discussed functionality is published as a separate package: https://pypi.python.org/pypi/typing-inspect https://github.com/ilevkivskyi/typing_inspect After the API is settled, some introspection functions may be added directly to typing. --

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: Cross-posting the link to upstream work on this: https://github.com/python/typing/pull/377 -- ___ Python tracker ___

[issue29262] Provide a way to check for *real* typing.Union instances

flying sheep added the comment: Cool! This set of basic initial check will consist of all the is_* functions that were mentioned right? FWIW I also think that this is the way to go, as it’s not obvious if the semantics should be “conforms to this type annotation” or “is a type annotation of

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: OK, I will make a PR to typing adding a folder (as it is done for mypy_extensions) with a basic set of runtime type inspection functions. -- ___ Python tracker

[issue29262] Provide a way to check for *real* typing.Union instances

Guido van Rossum added the comment: Up to you, but the latter might make it clearer that the two are to be kept in sync. -- ___ Python tracker ___

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: OK, I agree. How then it should be done logistically? Should I just make a separate repo on GitHub for this? Or will it be inside typing (like mypy_extesions is inside mypy) but published on PyPI separately? --

[issue29262] Provide a way to check for *real* typing.Union instances

Guido van Rossum added the comment: I think it should be separate from mypy_extensions, since it's not even related to mypy. Regarding typing.re and typing.io, typing.inspect would be a typed version of the inspect module, so that's not quite the same. (Though I consider typing.re/io mistakes

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: I have a similar idea. We already have mypy_extensions for runtime counterparts of experimental features. However, the runtime inspections are not related to mypy, so that I am not sure. I am just a bit worried there will be to many things to keep in mind/in

[issue29262] Provide a way to check for *real* typing.Union instances

Guido van Rossum added the comment: Posting to python-dev would probably cause more friction than a PR for the PEPs repo. But maybe the best way to do this is to use a third party module with a proposed API? E.g. typing_inspect. We could then iterate quickly on the design and implementation

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: > Maybe a proposal should be discussed as an addendum to PEP 484? Or would Mark Shannon reject that? On one hand, I would like to involve a wider audience to this discussion. On the other hand, an addition to the PEP could slow things down. Maybe a

[issue29262] Provide a way to check for *real* typing.Union instances

Guido van Rossum added the comment: Maybe a proposal should be discussed as an addendum to PEP 484? Or would Mark Shannon reject that? On Sun, Jan 15, 2017 at 2:48 PM, Ivan Levkivskyi wrote: > > Ivan Levkivskyi added the comment: > > > Maybe we need to take a step back

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: > Maybe we need to take a step back and look at the needs for code that wants > to implement runtime type checking more in general? I would say that the most convenient way for me would be a set of "inspect-style" simple helpers like ``is_union``,

[issue29262] Provide a way to check for *real* typing.Union instances

Guido van Rossum added the comment: Hm, let me back-pedal a bit. The situation with Callable is murky, as e.g. isinstance(typing.Tuple[int, int], typing.Callable) returns True. Maybe we need to take a step back and look at the needs for code that wants to implement runtime type checking more

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: This will be a bit unusual since ``isinstance`` is typically called for instances (i.e. not types) as in ``isinstance(func, Callable)``. But on the other hand this is probably what one would expect when one sees ``isinstance(tp, Union)``. Thus I am fine with

[issue29262] Provide a way to check for *real* typing.Union instances

Guido van Rossum added the comment: Hm, maybe isinstance(t, Union) should actually be allowed? (Though isinstance(x, Union[int, str]) should not be!) After all we can write isinstance(t, Callable) as well, even though isinstance(x, Callable[[int], int]) is disallowed. --

[issue29262] Provide a way to check for *real* typing.Union instances

Ivan Levkivskyi added the comment: In principle, such a function could be added if it is not called ``isinstance``. For example, we could add a helper ``is_union(tp)`` (or maybe also ``is_generic(tp)`` etc). Such function(s) will be simple one-liners wrapping private API in a right way (e.g.

[issue29262] Provide a way to check for *real* typing.Union instances

Evan added the comment: I'm also interested in this. I've been using 'thing.__origin__ is typing.Union', but this doesn't work in some of the older versions of typing. -- nosy: +evan_ ___ Python tracker

[issue29262] Provide a way to check for *real* typing.Union instances

New submission from flying sheep: typing.Union prevents the use of `isinstance` and `issubclass` via a hook. This is presumably to prevent errors that would arise if someone tried to do issubclass(A, Union[A, B]) or isinstance(A(), Union[A, B]), because Union isn’t specified in the PEP to