[Python-checkins] cpython (3.4): Issue #23572: Fixed functools.singledispatch on classes with falsy metaclasses.

Tue Aug 18 20:33:08 CEST 2015

https://hg.python.org/cpython/rev/586195685aaf
changeset: 97445:586195685aaf
branch: 3.4
parent: 97440:010264c9ceae
user: Yury Selivanov <yselivanov at sprymix.com>
date: Tue Aug 18 14:30:15 2015 -0400
summary:
 Issue #23572: Fixed functools.singledispatch on classes with falsy metaclasses.
Patch by Ethan Furman.
files:
 Lib/functools.py | 2 +-
 Lib/test/test_functools.py | 18 ++++++++++++++++++
 Misc/NEWS | 3 +++
 3 files changed, 22 insertions(+), 1 deletions(-)

diff --git a/Lib/functools.py b/Lib/functools.py
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -551,7 +551,7 @@
 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
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -1328,6 +1328,24 @@
 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
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -392,6 +392,9 @@
 - Issue #24298: Fix inspect.signature() to correctly unwrap wrappers
 around bound methods.
 
+- Issue #23572: Fixed functools.singledispatch on classes with falsy
+ metaclasses. Patch by Ethan Furman.
+
 IDLE
 ----
 
-- 
Repository URL: https://hg.python.org/cpython
