Skip to content

spec: clarify that passthrough __new__ is ignored when converting to callable #2314

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ashishpatel26 wants to merge 1 commit into
base: main
Choose a base branch
from
+5 −2
Open

spec: clarify that passthrough __new__ is ignored when converting to callable #2314

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
7 changes: 5 additions & 2 deletions docs/spec/constructors.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -387,7 +387,10 @@ constructor calls:
2. If the class defines a ``__new__`` method or inherits a ``__new__`` method
from a base class other than ``object``, a type checker should synthesize a
callable from the parameters and return type of that method after it is bound
to the class.
to the class. If the ``__new__`` method's only non-``cls`` parameters are

@JelleZijlstra JelleZijlstra Jun 23, 2026

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why is this the right behavior? Also shouldn't there be requirements on the type annotations for the args/kwargs parameters?

``*args`` and ``**kwargs`` (i.e. a passthrough), the method is considered
to not constrain the constructor signature, and this step produces no
callable type.

3. If the return type of the method in step 2 evaluates to a type that is not a
subclass of the class being constructed (or a union that includes such a
Expand Down Expand Up @@ -454,7 +457,7 @@ constructor calls:


reveal_type(accepts_callable(A)) # ``def () -> A``
reveal_type(accepts_callable(B)) # ``def (*args, **kwargs) -> B | def (x: int) -> B``
reveal_type(accepts_callable(B)) # ``def (x: int) -> B``
reveal_type(accepts_callable(C)) # ``def (x: int) -> int``
reveal_type(accepts_callable(D)) # ``def () -> NoReturn``
reveal_type(accepts_callable(E)) # ``def () -> A``
Expand Down