bpo-37880: for argparse add_argument with action='store_const', const now defaults to None. (GH-26707)

1 files changed, 19 insertions, 0 deletions

diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 0994e70..93ac0c3 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -745,6 +745,25 @@ class TestOptionalsActionAppendWithDefault(ParserTestCase):
     ]
 
 
+class TestConstActionsMissingConstKwarg(ParserTestCase):
+    """Tests that const gets default value of None when not provided"""
+
+    argument_signatures = [
+        Sig('-f', action='append_const'),
+        Sig('--foo', action='append_const'),
+        Sig('-b', action='store_const'),
+        Sig('--bar', action='store_const')
+    ]
+    failures = ['-f v', '--foo=bar', '--foo bar']
+    successes = [
+        ('', NS(f=None, foo=None, b=None, bar=None)),
+        ('-f', NS(f=[None], foo=None, b=None, bar=None)),
+        ('--foo', NS(f=None, foo=[None], b=None, bar=None)),
+        ('-b', NS(f=None, foo=None, b=None, bar=None)),
+        ('--bar', NS(f=None, foo=None, b=None, bar=None)),
+    ]
+
+
 class TestOptionalsActionAppendConst(ParserTestCase):
     """Tests the append_const action for an Optional"""