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gh-132139: 3.14 what's new: elaborate on why you can no longer set Union attributes #132157

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Apr 6, 2025
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gh-132139: 3.14 what's new: elaborate on why you can no longer set Union attributes #132157

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gh-132139: 3.14 what's new: elaborate on why you can no longer set `U…
AlexWaygood Apr 6, 2025
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Update Doc/whatsnew/3.14.rst
AlexWaygood Apr 6, 2025
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5 changes: 3 additions & 2 deletions Doc/whatsnew/3.14.rst
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Expand Up @@ -1130,8 +1130,9 @@ typing
For example, ``isinstance(int | str, typing.Union)`` will return ``True``; previously
this raised :exc:`TypeError`.
- The ``__args__`` attribute of :class:`typing.Union` objects is no longer writable.
- It is no longer possible to set arbitrary dunder attributes on :class:`typing.Union`
objects.
- It is no longer possible to set any attributes on :class:`typing.Union` objects.
This only ever worked for dunder attributes on previous versions, was never
documented to work, and was subtly broken in many cases.

(Contributed by Jelle Zijlstra in :gh:`105499`.)

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