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[3.12] gh-90015: Document that PEP-604 unions do not support forward references (GH-105366) #105460

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Jun 7, 2023
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[3.12] gh-90015: Document that PEP-604 unions do not support forward references (GH-105366) #105460

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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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