https://github.com/python/cpython/commit/70bc048e5cc5ae28663381bdc906292b5c5bf334
commit: 70bc048e5cc5ae28663381bdc906292b5c5bf334
branch: main
author: Dmitry Voropaev <[email protected]>
committer: savannahostrowski <[email protected]>
date: 2026-09-28T16:03:14Z
summary:
gh-110131: Document how a non-empty default works with append and extend
(#158155)
files:
M Doc/library/argparse.rst
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index c88c10030fb369..58f61a06d0512c 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -791,9 +791,9 @@ how the command-line arguments should be handled. The
supplied actions are:
* ``'append'`` - This appends each argument value to a list.
It is useful for allowing an option to be specified multiple times.
- If the default value is a non-empty list, the parsed value will start
- with the default list's elements and any values from the command line
- will be appended after those default values. Example usage::
+ If the default value is a non-empty list, the parsed value for the option
+ will start with the default list's elements and any values from the
+ command line will be appended after those default values. Example usage::
>>> parser = argparse.ArgumentParser()
>>> parser.add_argument('--foo', action='append', default=['0'])
@@ -818,12 +818,16 @@ how the command-line arguments should be handled. The
supplied actions are:
value ``'+'`` or ``'*'``.
Note that when nargs_ is ``None`` (the default) or ``'?'``, each
character of the argument string will be appended to the list.
+ If the default value is a non-empty list, the parsed value for the option
+ will start with the default list's elements and any values from the
+ command line will be appended after those default values.
Example usage::
>>> parser = argparse.ArgumentParser()
- >>> parser.add_argument("--foo", action="extend", nargs="+", type=str)
+ >>> parser.add_argument("--foo", action="extend", nargs="+", type=str,
+ ... default=["d1"])
>>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
- Namespace(foo=['f1', 'f2', 'f3', 'f4'])
+ Namespace(foo=['d1', 'f1', 'f2', 'f3', 'f4'])
.. versionadded:: 3.8
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