merge #15847: allow args to be a tuple in parse_args

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.

1 files changed, 4 insertions, 1 deletions

diff --git a/Lib/argparse.py b/Lib/argparse.py
index adecb88f0e..d5976e9f4f 100644
--- a/Lib/argparse.py
+++ b/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: