bpo-42317: Improve docs of typing.get_args concerning Union (GH-23254)

diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
index 9a993c073277f9c519d8926bdec62738bc8ade74..a8de984a5ce41b63cd1bdb945bde9d6c1b1a9877 100644 (file)
--- a/Doc/library/typing.rst
+++ b/Doc/library/typing.rst
@@ -1706,6 +1706,9 @@ Introspection helpers
    For a typing object of the form ``X[Y, Z, ...]`` these functions return
    ``X`` and ``(Y, Z, ...)``. If ``X`` is a generic alias for a builtin or
    :mod:`collections` class, it gets normalized to the original class.
+   If ``X`` is a :class:`Union` contained in another generic type,
+   the order of ``(Y, Z, ...)`` may be different from the order of
+   the original arguments ``[Y, Z, ...]`` due to type caching.
    For unsupported objects return ``None`` and ``()`` correspondingly.
    Examples::