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gh-115881: Document feature_version limitations (#115980)

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Shantanu 2024-02-29 03:09:09 -08:00 committed by GitHub
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Doc/library/ast.rst
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@ -2183,12 +2183,15 @@ and classes for traversing abstract syntax trees:
modified to correspond to :pep:`484` "signature type comments",
e.g. ``(str, int) -> List[str]``.
Also, setting ``feature_version`` to a tuple ``(major, minor)``
will attempt to parse using that Python version's grammar.
Currently ``major`` must equal to ``3``. For example, setting
``feature_version=(3, 4)`` will allow the use of ``async`` and
``await`` as variable names. The lowest supported version is
``(3, 7)``; the highest is ``sys.version_info[0:2]``.
Setting ``feature_version`` to a tuple ``(major, minor)`` will result in
a "best-effort" attempt to parse using that Python version's grammar.
For example, setting ``feature_version=(3, 9)`` will attempt to disallow
parsing of :keyword:`match` statements.
Currently ``major`` must equal to ``3``. The lowest supported version is
``(3, 7)`` (and this may increase in future Python versions);
the highest is ``sys.version_info[0:2]``. "Best-effort" attempt means there
is no guarantee that the parse (or success of the parse) is the same as
when run on the Python version corresponding to ``feature_version``.
If source contains a null character ('\0'), :exc:`ValueError` is raised.