fix(argparse): raise error when BooleanOptionalAction used with prefix_chars without '-'

Author: mattwang44

Lib/argparse.py

@@ -954,6 +954,9 @@ def __init__(self,
 
 
     def __call__(self, parser, namespace, values, option_string=None):
+        if '-' not in parser.prefix_chars:
+            raise ValueError("BooleanOptionalAction requires '-' in parser's prefix_chars")
+        
         if option_string in self.option_strings:
             setattr(namespace, self.dest, not option_string.startswith('--no-'))
 

Lib/test/test_argparse.py

@@ -795,6 +795,16 @@ def test_invalid_name(self):
         self.assertEqual(str(cm.exception),
                          "invalid option name '--no-foo' for BooleanOptionalAction")
 
+    def test_prefix_chars_incompatibility(self):
+        parser = argparse.ArgumentParser(prefix_chars='+')
+        parser.add_argument('++foo', action=argparse.BooleanOptionalAction)
+        
+        with self.assertRaises(ValueError) as cm:
+            parser.parse_args(['++foo'])
+        
+        self.assertIn(str(cm.exception),
+                      "BooleanOptionalAction requires '-' in parser's prefix_chars")
+
 class TestBooleanOptionalActionRequired(ParserTestCase):
     """Tests BooleanOptionalAction required"""