Use match/case for isinstance dispatch - #14799
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Replace the ``isinstance`` dispatch on ``obj`` with class patterns. The falsy check stays an ``if`` with an early return, as truthiness has no pattern equivalent. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Replace the ``isinstance``/identity dispatch on ``val`` with class patterns. The ``NOTSET`` identity test becomes a ``NotSetType()`` class pattern: ``NotSetType`` has a single member, so it is equivalent to the ``val is NOTSET`` test, while the ``NotSetType.token`` value pattern would not be, as value patterns compare with ``==`` and parameter values are allowed to have an ``__eq__`` that raises. It still has to be matched before the ``enum.Enum()`` arm, as ``NOTSET`` is an ``enum.Enum``. The ``__name__`` sniffing arm has no pattern equivalent and stays a guard. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Replace the ``isinstance`` dispatch on the expected exception with class patterns; the unreachable ``else`` arm becomes ``case _``. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Same spirit as #13762, but outside assert_repr. Focused on the isinstance chained check to convert them to match case.