Add support for Annotated in is_subtype (transparently ignoring the annotations)

[apirogov]

In my project I am using pydantic and use its Field(...) configuration e.g. to define alias names for keys within Annotated, e.g.

x: Annotated[int, Field(alias="y")]

but I need to check is_subtype on the wrapped types (I don't use the annotation for any type-domain related info).

It would be great if Annotated could be transparently ignored.

I understand there are many "semantics" one could give to checking Annotated types, but as the annotation is quite arbitrary and tool specific, I think that simply ignoring the annotation and recursing down the actual type would be the "right" default behavior.

A more conservative solution I would also be happy with would be to have this as some keyword argument to is_subtype, called e.g. ignore_annotations to have that behavior and do with them whatever you believe would make more sense as the default.

But in my case, the annotation object (pydantic.FieldInfo) does not have even equality, so this would not work for me to check that the annotations must all be equal or something like that. Thats why I think it does not make any sense to try doing anything with the annotations but ignoring them, as it probably would not work in the general case.

[erezsh]

Is the Annotated object always top-level? Because if so, it should be easy to write a function remove_annotations, that simply unwraps them before calling is_subtype.

[apirogov]

That is currently what I am doing, and it's working fine - for now :) But I'd rather remove the workaround if possible.

I don't think there is any restriction prohibiting Annotated nesting (also why should there be? you might attach e.g. analysis information / any kind of metadata on various levels of composed types).

I just thought it would be a neat thing to have a clean solution instead of such a use-case specific "hack" (and I am not sure whether this will be sufficient on the long term, if more and more Python libraries adopt typehint-based stuff and place their magic into the annotations). And After all, Annotated is a standard hint included in typing in the recent Python versions.

[erezsh]

Sorry, I misunderstood, I thought you're talking about a feature that's specific to pydantic.

Yeah, I agree, runtype should cover everything that's in typing. I'll see if I can find time for it soon.

[erezsh]

@apirogov Should be now fixed in master.

[apirogov]

In Python 3.8 Annotated is in typing_extensions and it does not seem to work:

is_subtype(List[int], Annotated[List[Annotated[int, "hello"]], "world"])) yields

NotImplementedError: ('No support for type:', typing_extensions.Annotated[typing.List[typing_extensions.Annotated[int, 'hello']], 'world'])

(expected: types are equivalent, i.e. True in both directions)

[erezsh]

I think I fixed it!