From a99c7dedcb9310d80f2cf29a747e05fdde2716bc Mon Sep 17 00:00:00 2001
From: R David Murray <rdmurray@bitdance.com>
Date: Sat, 8 Sep 2012 12:15:25 -0400
Subject: [PATCH] #15847: allow args to be a tuple in parse_args
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This fixes a regression introduced by the fix for issue #13922.  Although args
is not documented as being allowed to be a tuple, previously this worked and
so naturally there are programs in the field that depend on it.

Patch by Zbyszek Jędrzejewski-Szmek.
---
 Lib/argparse.py           |  5 ++++-
 Lib/test/test_argparse.py | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Lib/argparse.py b/Lib/argparse.py
index a73845594f5..ab8ff2faec1 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1692,9 +1692,12 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         return args
 
     def parse_known_args(self, args=None, namespace=None):
-        # args default to the system args
         if args is None:
+            # args default to the system args
             args = _sys.argv[1:]
+        else:
+            # make sure that args are mutable
+            args = list(args)
 
         # default Namespace built from parser defaults
         if namespace is None:
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 77f5aca21e0..99c1babb4ac 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -4486,6 +4486,24 @@ class TestTypeFunctionCallWithNonStringDefault(TestCase):
 
 class TestParseKnownArgs(TestCase):
 
+    def test_arguments_tuple(self):
+        parser = argparse.ArgumentParser()
+        parser.parse_args(())
+
+    def test_arguments_list(self):
+        parser = argparse.ArgumentParser()
+        parser.parse_args([])
+
+    def test_arguments_tuple_positional(self):
+        parser = argparse.ArgumentParser()
+        parser.add_argument('x')
+        parser.parse_args(('x',))
+
+    def test_arguments_list_positional(self):
+        parser = argparse.ArgumentParser()
+        parser.add_argument('x')
+        parser.parse_args(['x'])
+
     def test_optionals(self):
         parser = argparse.ArgumentParser()
         parser.add_argument('--foo')