From aa32a7e1116f7aaaef9fec453db910e90ab7b101 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Batuhan=20Ta=C5=9Fkaya?=
 <47358913+isidentical@users.noreply.github.com>
Date: Tue, 21 May 2019 20:47:42 +0300
Subject: bpo-23378: Add an extend action to argparse (GH-13305)

Add an extend action to argparse


https://bugs.python.org/issue23378
---
 Doc/library/argparse.rst                                         | 9 +++++++++
 Lib/argparse.py                                                  | 7 +++++++
 Lib/test/test_argparse.py                                        | 9 +++++++++
 .../NEWS.d/next/Library/2019-05-14-05-38-22.bpo-23378.R25teI.rst | 1 +
 4 files changed, 26 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2019-05-14-05-38-22.bpo-23378.R25teI.rst

diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index cef197f..b77a38c 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -797,6 +797,15 @@ 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'])
+
 You may also specify an arbitrary action by passing an Action subclass or
 other object that implements the same interface.  The recommended way to do
 this is to extend :class:`Action`, overriding the ``__call__`` method
diff --git a/Lib/argparse.py b/Lib/argparse.py
index 798766f..ef888f0 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1154,6 +1154,12 @@ class _SubParsersAction(Action):
             vars(namespace).setdefault(_UNRECOGNIZED_ARGS_ATTR, [])
             getattr(namespace, _UNRECOGNIZED_ARGS_ATTR).extend(arg_strings)
 
+class _ExtendAction(_AppendAction):
+    def __call__(self, parser, namespace, values, option_string=None):
+        items = getattr(namespace, self.dest, None)
+        items = _copy_items(items)
+        items.extend(values)
+        setattr(namespace, self.dest, items)
 
 # ==============
 # Type classes
@@ -1262,6 +1268,7 @@ class _ActionsContainer(object):
         self.register('action', 'help', _HelpAction)
         self.register('action', 'version', _VersionAction)
         self.register('action', 'parsers', _SubParsersAction)
+        self.register('action', 'extend', _ExtendAction)
 
         # raise an exception if the conflict handler is invalid
         self._get_handler()
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index e849c7b..9d68f40 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -1786,6 +1786,15 @@ class TestActionRegistration(TestCase):
         self.assertEqual(parser.parse_args(['42']), NS(badger='foo[42]'))
 
 
+class TestActionExtend(ParserTestCase):
+    argument_signatures = [
+        Sig('--foo', action="extend", nargs="+", type=str),
+    ]
+    failures = ()
+    successes = [
+        ('--foo f1 --foo f2 f3 f4', NS(foo=['f1', 'f2', 'f3', 'f4'])),
+    ]
+
 # ================
 # Subparsers tests
 # ================
diff --git a/Misc/NEWS.d/next/Library/2019-05-14-05-38-22.bpo-23378.R25teI.rst b/Misc/NEWS.d/next/Library/2019-05-14-05-38-22.bpo-23378.R25teI.rst
new file mode 100644
index 0000000..c7c3f17
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-05-14-05-38-22.bpo-23378.R25teI.rst
@@ -0,0 +1 @@
+Add an extend action to argparser.
-- 
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