Issue #23572: Fixed functools.singledispatch on classes with falsy metaclasses.
Patch by Ethan Furman.
diff --git a/Lib/functools.py b/Lib/functools.py
index 09df068..06a4ff1 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -567,7 +567,7 @@
break # reject the current head, it appears later
else:
break
- if not candidate:
+ if candidate is None:
raise RuntimeError("Inconsistent hierarchy")
result.append(candidate)
# remove the chosen candidate
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index ac211c4..ae929ec 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -1491,6 +1491,24 @@
many_abcs = [c.Mapping, c.Sized, c.Callable, c.Container, c.Iterable]
self.assertEqual(mro(X, abcs=many_abcs), expected)
+ def test_false_meta(self):
+ # see issue23572
+ class MetaA(type):
+ def __len__(self):
+ return 0
+ class A(metaclass=MetaA):
+ pass
+ class AA(A):
+ pass
+ @functools.singledispatch
+ def fun(a):
+ return 'base A'
+ @fun.register(A)
+ def _(a):
+ return 'fun A'
+ aa = AA()
+ self.assertEqual(fun(aa), 'fun A')
+
def test_mro_conflicts(self):
c = collections
@functools.singledispatch