diff options
Diffstat (limited to 'Lib/test/test_contains.py')
| -rw-r--r-- | Lib/test/test_contains.py | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/Lib/test/test_contains.py b/Lib/test/test_contains.py index 3c6bdeffda..036a1d012d 100644 --- a/Lib/test/test_contains.py +++ b/Lib/test/test_contains.py @@ -84,6 +84,31 @@ class TestContains(unittest.TestCase): self.assertTrue(container == constructor(values)) self.assertTrue(container == container) + def test_block_fallback(self): + # blocking fallback with __contains__ = None + class ByContains(object): + def __contains__(self, other): + return False + c = ByContains() + class BlockContains(ByContains): + """Is not a container + + This class is a perfectly good iterable (as tested by + list(bc)), as well as inheriting from a perfectly good + container, but __contains__ = None prevents the usual + fallback to iteration in the container protocol. That + is, normally, 0 in bc would fall back to the equivalent + of any(x==0 for x in bc), but here it's blocked from + doing so. + """ + def __iter__(self): + while False: + yield None + __contains__ = None + bc = BlockContains() + self.assertFalse(0 in c) + self.assertFalse(0 in list(bc)) + self.assertRaises(TypeError, lambda: 0 in bc) if __name__ == '__main__': unittest.main() |