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Writing stubs: Various updates #2387

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Writing stubs: Various updates #2387

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Writing stubs: Various updates
srittau Nov 9, 2026
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srittau Nov 9, 2026
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18 changes: 14 additions & 4 deletions docs/guides/writing_stubs.rst
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Expand Up @@ -237,7 +237,7 @@ annotated with ``_typeshed.Incomplete`` (`documentation <https://github.com/pyth

``_typeshed.Incomplete`` can also be used for partially known types::

def foo(x: Incomplete | None = None) -> list[Incomplete]: ...
def foo(x: Incomplete | None) -> list[Incomplete]: ...

Partial stubs can be useful, especially for larger packages, but they should
follow the following guidelines:
Expand Down Expand Up @@ -647,6 +647,18 @@ No::
def foo(x: X = X()) -> None: ...
def bar(y: str = None) -> None: ...

*Exception:* If ``X`` is ``Incomplete`` and has a ``None`` default, leave the
argument unannotated.

Yes::

def incomplete1(z: Incomplete | None) -> None: ...
def incomplete2(z=None) -> None: ...

No::

def incomplete(z: Incomplete | None = None): ...

Comment on lines +650 to +661

@jorenham jorenham Nov 9, 2026

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I don't agree with this, see #2387 (comment). So can we leave this out? The other bits I'm fine with, so if you want we can discuss this further in a separate PR for this part.

Do not annotate ``self`` and ``cls`` in method definitions unless an explicit
annotation is needed to constrain or relax the receiver type.

Expand Down Expand Up @@ -690,12 +702,10 @@ No::
def to_int3(x: str) -> int: pass

Avoid invariant collection types (``list``, ``dict``) for function parameters,
in favor of covariant types like ``Mapping`` or ``Sequence``.
in favor of covariant protocols and other types like ``Iterable`` or ``Mapping``.

Avoid union return types. See https://github.com/python/mypy/issues/1693

Use ``float`` instead of ``int | float`` for parameter annotations. See :pep:`484` for more details.

Language Features
-----------------

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