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gh-161007: Add a glossary entry for "virtual subclass" #161182

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gh-161007: Add a glossary entry for "virtual subclass"
thejesh23 Nov 2, 2026
9d7e124
Keep "virtual subclass" tied to ABCMeta.register(), as in the abc docs
thejesh23 Nov 2, 2026
12b73d8
Address review: drop the __subclasshook__ and MRO sentences
thejesh23 Nov 3, 2026
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13 changes: 10 additions & 3 deletions Doc/glossary.rst
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Expand Up @@ -29,9 +29,10 @@ Glossary
Abstract base classes complement :term:`duck-typing` by
providing a way to define interfaces when other techniques like
:func:`hasattr` would be clumsy or subtly wrong (for example with
:ref:`magic methods <special-lookup>`). ABCs introduce virtual
subclasses, which are classes that don't inherit from a class but are
still recognized by :func:`isinstance` and :func:`issubclass`; see the
:ref:`magic methods <special-lookup>`). ABCs introduce
:term:`virtual subclasses <virtual subclass>`, which are classes that
don't inherit from a class but are still recognized by
:func:`isinstance` and :func:`issubclass`; see the
:mod:`abc` module documentation. Python comes with many built-in ABCs for
data structures (in the :mod:`collections.abc` module), numbers (in the
:mod:`numbers` module), streams (in the :mod:`io` module), import finders
Expand Down Expand Up @@ -1727,6 +1728,12 @@ Glossary
A computer defined entirely in software. Python's virtual machine
executes the :term:`bytecode` emitted by the bytecode compiler.

virtual subclass
A class that :func:`issubclass` and :func:`isinstance` treat as a
subclass of an :term:`abstract base class` even though it does not
inherit from it. A class is made a virtual subclass by registering
it with the ABC's :meth:`~abc.ABCMeta.register` method.

walrus operator
A light-hearted way to refer to the :ref:`assignment expression
<assignment-expressions>` operator ``:=`` because it looks a bit like a
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