[New-bugs-announce] [issue46195] Annotated and Optional get_type_hints buggy interaction

[Mehdi2277]

New submission from Mehdi2277 <med2277 at gmail.com>:

This is two closely related issues with get_type_hints on an optional annotated member. I'm testing with Annotated/get_type_hints from typing extensions on 3.8 and assuming they're backport equivalent to current behavior.

The first issue is get_type_hints has inconsistent behavior depending on whether annotation comes from a function with a None default or an attribute with a None default.

class Foo:
    def __init__(
        self,
        x: 
            Annotated[Optional[str], "doc string"] = None,
    ):
        ...

class Foo2:
    x: Annotated[Optional[str], "doc string"] = None

get_type_hints(Foo.__init__) 
# {'x': typing.Union[typing_extensions.Annotated[typing.Union[str, NoneType], 'doc string'], NoneType]}

get_type_hints(Foo2)
# {'x': typing_extensions.Annotated[typing.Union[str, NoneType], 'doc string']}

Attributes with a None default are not wrapped by get_type_hints, but function parameters. Which of the two behaviors is correct I don't know, but I'd expect the two to be equivalent annotations.

The second issue is for function arguments with a None default the optional wrapper happens even if the type inside annotated already has optional. Example,

from typing_extensions import Annotated, get_type_hints

class Foo:
    def __init__(
        self,
        x: 
            Annotated[Optional[str], "doc string"] = None,
    ):
        ...

get_type_hints(Foo.__init__, include_extras=True)
# {'x': typing.Union[typing_extensions.Annotated[typing.Union[str, NoneType], 'doc string'], NoneType]}


For Annotated types I would expect any type rules like wrapping to apply only to the first argument and not the entire annotation. I mainly ran into this for a runtime type introspection library (similar in spirit to pydantic).

As a note include_extras being True or False while it changes type is an issue in either case. With include_extras as False the Annotated goes away, but the type still gets double wrapped as an Optional.

----------
messages: 409319
nosy: gvanrossum, kj, med2277
priority: normal
severity: normal
status: open
title: Annotated and Optional get_type_hints buggy interaction
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue46195>
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