Fix bug with argparse.Parser.parse_args(*args)

Lib/argparse.py

@@ -1709,9 +1709,12 @@ 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:

Lib/test/test_argparse.py

@@ -4565,6 +4565,24 @@ class TestMessageContentError(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')