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[3.15] gh-149083: Document that dataclasses.MISSING and KW_ONLY are sentinels (GH-155919) by miss-islington · Pull Request #155927 · python/cpython · GitHub

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[3.15] gh-149083: Document that dataclasses.MISSING and KW_ONLY are sentinels (GH-155919) #155927

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hugovk merged 1 commit into from
Aug 17, 2026
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[3.15] gh-149083: Document that dataclasses.MISSING and KW_ONLY are sentinels (GH-155919) #155927

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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 @@ -523,11 +523,14 @@ 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 @@ -552,6 +555,9 @@ 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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