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| author | Alex Waygood <Alex.Waygood@Gmail.com> | 2023-06-07 17:26:23 (GMT) |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2023-06-07 17:26:23 (GMT) |
| commit | fbdee000de47ae96fbf53ce8908e8efbb23cfba4 (patch) | |
| tree | 2cfceaf576236eb4a4db4b862096fde7be732a6b /Doc/library/stdtypes.rst | |
| parent | c85be33acc29f36e07b6220b17f994de7e71801b (diff) | |
| download | cpython-fbdee000de47ae96fbf53ce8908e8efbb23cfba4.zip cpython-fbdee000de47ae96fbf53ce8908e8efbb23cfba4.tar.gz cpython-fbdee000de47ae96fbf53ce8908e8efbb23cfba4.tar.bz2 | |
gh-90015: Document that PEP-604 unions do not support forward references (#105366)
Diffstat (limited to 'Doc/library/stdtypes.rst')
| -rw-r--r-- | Doc/library/stdtypes.rst | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst index fdef531..0caa725 100644 --- a/Doc/library/stdtypes.rst +++ b/Doc/library/stdtypes.rst @@ -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: |