Mailman 3 July 2022 - Typing-sig

A way to typehint a return type in parent based on return type of a child
by Stanislav Zmiev 04 Jul '22

04 Jul '22

A duplicate of https://discuss.python.org/t/a-way-to-typehint-a-return-type-in-parent-base… Both in my personal projects and at two of my workplaces I have found a specific case that python typehints cannot handle well enough. ```python from abc import abstractmethod, ABC class A(ABC): def process_child_method(self): child_return = self.child_method() # Some actions on the return of the method ... return child_return @abstractmethod def child_method(self): pass class B(A): def child_method(self) -> int: return 83 b = B() b.process_child_method() # None, according to pyright ``` The only way to handle it right now is to use Generics but that creates a weird decoupling in terms of typehints: ```python from typing import Generic, TypeVar from abc import abstractmethod, ABC T = TypeVar("T") class A(ABC, Generic[T]): def process_child_method(self) -> T: child_return = self.child_method() # Some actions on the return of the method ... return child_return @abstractmethod def child_method(self) -> T: pass class B(A[int]): def child_method(self) -> int: return 83 b = B() b.process_child_method() # int ``` which could easily lead to typehints lying in large classes where we are not careful such as: ```python class C(A[int]): # Many lines of code here ... def child_method(self) -> str: return "83" ``` My examples are a bit esoteric and I do not necessarily consider this to be a good pattern but I believe we should have some way of describing "returns the same object as another method in the class". Let's discuss this. I guess this introduces dependencies into typehints which could become rather buggy and hard to manage but maybe we can figure out some nice way of handling such cases. Something like a DependencyVariable or even just adding support for such cases into TypeVar. I also understand that this is mostly the business of the tool creators but the original peps for typing also haven't covered this use case.

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Opened and changed typing issues week 2022-W26
by Typing Bot 04 Jul '22

04 Jul '22

The following is an overview of all issues and pull requests in the typing repository on GitHub with the label 'topic: feature' that were opened or updated last week, excluding closed issues. --------------------------------------------------- The following issues and pull requests were updated last week: #956 (🎁) Add a `StubOnlyBase` decorator for types that don't actually extend things, but do in the stubs (like `Generic`) opened by @KotlinIsland https://github.com/python/typing/issues/956 #1216 TypeVarTuple Transformations Before Unpack opened by @llchan https://github.com/python/typing/issues/1216 --------------------------------------------------- All issues and pull requests with the label 'topic: feature' can be viewed under the following URL: https://github.com/python/typing/issues?q=label%3A%22topic%3A+feature%22

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Forward References in UnionType?
by Paul Bryan 02 Jul '22

02 Jul '22

With Union, forward references in strings get converted to ForwardRef. To wit: >>> from typing import Union >>> Alias = Union[str, "Foo"] >>> Alias typing.Union[str, ForwardRef('Foo')] With the new UnionType, the following is not valid: >>> Alias = str | "Foo" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for |: 'type' and 'str' The following is also invalid: >>> from typing import ForwardRef >>> Alias = str | ForwardRef("Foo") Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for |: 'type' and 'ForwardRef' Having the whole type alias as a string doesn't quite make sense to me, but maybe it's in fact correct: >>> Alias = "str | Foo" >>> Alias 'str | Foo' I see this open BPO, which was discussed in 2021: https://bugs.python.org/issue45857 Any suggestions on how else to make forward references in type aliases with the new UnionType?

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typing-extensions 4.3.0 released
by Jelle Zijlstra 01 Jul '22

01 Jul '22

I just released typing-extensions 4.3.0: https://pypi.org/project/typing-extensions/4.3.0/ The release adds runtime support for generic NamedTuple and TypedDict, both contributed by Alex Waygood.

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