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gh-149083: Document that dataclasses.MISSING and KW_ONLY are sentinels #155919

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hugovk merged 4 commits into from
Aug 17, 2026
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gh-149083: Document that dataclasses.MISSING and KW_ONLY are sentinels #155919

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fe79822
gh-149083: Document that dataclasses.MISSING and KW_ONLY are sentinels
fregataa Aug 17, 2026
fbf26cd
Drop the repr mention from the sentinel versionchanged notes
fregataa Aug 17, 2026
213db85
Simplify the sentinel versionchanged notes
fregataa Aug 17, 2026
69cff04
Mark up default_factory as a parameter
fregataa Aug 17, 2026
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14 changes: 10 additions & 4 deletions Doc/library/dataclasses.rst
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Expand Up @@ -262,8 +262,8 @@ Module contents
c = C()
c.mylist += [1, 2, 3]

As shown above, the :const:`MISSING` value is a sentinel object used to
detect if some parameters are provided by the user. This sentinel is
As shown above, the :const:`MISSING` value is a :class:`sentinel` object
used to detect if some parameters are provided by the user. This sentinel is
used because ``None`` is a valid value for some parameters with
a distinct meaning. No code should directly use the :const:`MISSING` value.

Expand Down Expand Up @@ -528,11 +528,14 @@ Module contents

.. data:: MISSING

A sentinel value signifying a missing default or default_factory.
A :class:`sentinel` object signifying a missing default or *default_factory*.

.. versionchanged:: 3.15
:const:`!MISSING` is now a :class:`sentinel` object.

.. data:: KW_ONLY

A sentinel value used as a type annotation. Any fields after a
A :class:`sentinel` object used as a type annotation. Any fields after a
pseudo-field with the type of :const:`!KW_ONLY` are marked as
keyword-only fields. Note that a pseudo-field of type
:const:`!KW_ONLY` is otherwise completely ignored. This includes the
Expand All @@ -557,6 +560,9 @@ Module contents

.. versionadded:: 3.10

.. versionchanged:: 3.15
:const:`!KW_ONLY` is now a :class:`sentinel` object.

.. exception:: FrozenInstanceError

Raised when an implicitly defined :meth:`~object.__setattr__` or
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