Closes #12579. Positional fields with str.format_map() now raise a ValueError instead of SystemError.
diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index 885e740..55aaba6 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -736,6 +736,11 @@
self.assertRaises(TypeError, '{a'.format_map)
self.assertRaises(TypeError, '}a'.format_map)
+ # issue #12579: can't supply positional params to format_map
+ self.assertRaises(ValueError, '{}'.format_map, {'a' : 2})
+ self.assertRaises(ValueError, '{}'.format_map, 'a')
+ self.assertRaises(ValueError, '{a} {}'.format_map, {"a" : 2, "b" : 1})
+
def test_format_auto_numbering(self):
class C:
def __init__(self, x=100):