bpo-34850: Emit a warning for "is" and "is not" with a literal. (GH-9642)
diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 3d8b151..3ed19ff 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -1226,11 +1226,33 @@
if 1 > 1: pass
if 1 <= 1: pass
if 1 >= 1: pass
- if 1 is 1: pass
- if 1 is not 1: pass
+ if x is x: pass
+ if x is not x: pass
if 1 in (): pass
if 1 not in (): pass
- if 1 < 1 > 1 == 1 >= 1 <= 1 != 1 in 1 not in 1 is 1 is not 1: pass
+ if 1 < 1 > 1 == 1 >= 1 <= 1 != 1 in 1 not in x is x is not x: pass
+
+ def test_comparison_is_literal(self):
+ def check(test, msg='"is" with a literal'):
+ with self.assertWarnsRegex(SyntaxWarning, msg):
+ compile(test, '<testcase>', 'exec')
+ with warnings.catch_warnings():
+ warnings.filterwarnings('error', category=SyntaxWarning)
+ with self.assertRaisesRegex(SyntaxError, msg):
+ compile(test, '<testcase>', 'exec')
+
+ check('x is 1')
+ check('x is "thing"')
+ check('1 is x')
+ check('x is y is 1')
+ check('x is not 1', '"is not" with a literal')
+
+ with warnings.catch_warnings():
+ warnings.filterwarnings('error', category=SyntaxWarning)
+ compile('x is None', '<testcase>', 'exec')
+ compile('x is False', '<testcase>', 'exec')
+ compile('x is True', '<testcase>', 'exec')
+ compile('x is ...', '<testcase>', 'exec')
def test_binary_mask_ops(self):
x = 1 & 1
@@ -1520,9 +1542,11 @@
self.assertEqual(16 // (4 // 2), 8)
self.assertEqual((16 // 4) // 2, 2)
self.assertEqual(16 // 4 // 2, 2)
- self.assertTrue(False is (2 is 3))
- self.assertFalse((False is 2) is 3)
- self.assertFalse(False is 2 is 3)
+ x = 2
+ y = 3
+ self.assertTrue(False is (x is y))
+ self.assertFalse((False is x) is y)
+ self.assertFalse(False is x is y)
def test_matrix_mul(self):
# This is not intended to be a comprehensive test, rather just to be few