8000 [3.13] gh-84545: Clarify the 'extend' action documentation in argparse (GH-125870) by miss-islington · Pull Request #125964 · python/cpython · GitHub
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[3.13] gh-84545: Clarify the 'extend' action documentation in argparse (GH-125870) #125964

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Oct 26, 2024
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[3.13] gh-84545: Clarify the 'extend' action documentation in argparse (GH-125870) #125964

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26 changes: 15 additions & 11 deletions Doc/library/argparse.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -692,6 +692,21 @@ how the command-line arguments should be handled. The supplied actions are:
>>> parser.parse_args('--str --int'.split())
Namespace(types=[<class 'str'>, <class 'int'>])

* ``'extend'`` - This stores a list and appends each item from the multi-value
argument list to it.
The ``'extend'`` action is typically used with the nargs_ keyword argument
value ``'+'`` or ``'*'``.
Note that when nargs_ is ``None`` (the default) or ``'?'``, each
character of the argument string will be appended to the list.
Example usage::

>>> parser = argparse.ArgumentParser()
>>> parser.add_argument("--foo", action="extend", nargs="+", type=str)
>>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
Namespace(foo=['f1', 'f2', 'f3', 'f4'])

.. versionadded:: 3.8

* ``'count'`` - This counts the number of times a keyword argument occurs. For
example, this is useful for increasing verbosity levels::

Expand All @@ -717,17 +732,6 @@ how the command-line arguments should be handled. The supplied actions are:
>>> parser.parse_args(['--version'])
PROG 2.0

* ``'extend'`` - This stores a list, and extends each argument value to the
list.
Example usage::

>>> parser = argparse.ArgumentParser()
>>> parser.add_argument("--foo", action="extend", nargs="+", type=str)
>>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
Namespace(foo=['f1', 'f2', 'f3', 'f4'])

.. versionadded:: 3.8

Only actions that consume command-line arguments (e.g. ``'store'``,
``'append'`` or ``'extend'``) can be used with positional arguments.

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