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gh-90015: Document that PEP-604 unions do not support forward references #105366

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Merged
merged 8 commits into from
Jun 7, 2023
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gh-90015: Document that PEP-604 unions do not support forward references #105366

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Document that PEP-604 unions do not support forward references as str…
AlexWaygood Jun 6, 2023
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fiddle
AlexWaygood Jun 6, 2023
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Be more hand-wavy
AlexWaygood Jun 7, 2023
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Merge branch 'python:main' into 604-forward-refs
AlexWaygood Jun 7, 2023
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Update Doc/library/stdtypes.rst
AlexWaygood Jun 7, 2023
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Clarify that this is only a runtime limitation
AlexWaygood Jun 7, 2023
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Update Doc/library/stdtypes.rst
AlexWaygood Jun 7, 2023
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Update Doc/library/stdtypes.rst
AlexWaygood Jun 7, 2023
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8 changes: 8 additions & 0 deletions Doc/library/stdtypes.rst
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Expand Up @@ -5162,6 +5162,14 @@ enables cleaner type hinting syntax compared to :data:`typing.Union`.
def square(number: int | float) -> int | float:
return number ** 2

.. note::

The ``|`` operand cannot be used at runtime to define unions where one or
more members is a forward reference. For example, ``int | "Foo"``, where
``"Foo"`` is a reference to a class not yet defined, will fail at
runtime. For unions which include forward references, present the
whole expression as a string, e.g. ``"int | Foo"``.

.. describe:: union_object == other

Union objects can be tested for equality with other union objects. Details:
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