[3.13] GH-61082: Clarify nargs='*' positional default behavior (GH-150989) (#151170)

GH-61082: Clarify nargs='*' positional default behavior (GH-150989)
(cherry picked from commit bc37a227b2f481d0f260f9beae5229e8d432a0cc)

Co-authored-by: Savannah Ostrowski <savannah@python.org>

diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index 89b9faf9f60d2ad6f3fd55df0810bf966a8dca15..fa5b92ed81b85a32ad7def8a86d3257e185017bd 100644 (file)
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -953,6 +953,10 @@ is used when no command-line argument was present::
    >>> parser.parse_args([])
    Namespace(foo=42)
 
+Because ``nargs='*'`` gathers any supplied values into a list, an absent
+positional argument yields an empty list (``[]``). Only a non-``None``
+*default* overrides this (so ``default=None`` still gives ``[]``).
+
 For required_ arguments, the ``default`` value is ignored. For example, this
 applies to positional arguments with nargs_ values other than ``?`` or ``*``,
 or optional arguments marked as ``required=True``.