changeset:   97445:586195685aaf
branch:      3.4
parent:      97440:010264c9ceae
user:        Yury Selivanov <yselivanov@sprymix.com>
date:        Tue Aug 18 14:30:15 2015 -0400
files:       Lib/functools.py Lib/test/test_functools.py Misc/NEWS
description:
Issue #23572: Fixed functools.singledispatch on classes with falsy metaclasses.

Patch by Ethan Furman.


diff -r 010264c9ceae -r 586195685aaf Lib/functools.py
--- a/Lib/functools.py	Tue Aug 18 13:26:57 2015 -0400
+++ b/Lib/functools.py	Tue Aug 18 14:30:15 2015 -0400
@@ -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 -r 010264c9ceae -r 586195685aaf Lib/test/test_functools.py
--- a/Lib/test/test_functools.py	Tue Aug 18 13:26:57 2015 -0400
+++ b/Lib/test/test_functools.py	Tue Aug 18 14:30:15 2015 -0400
@@ -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 -r 010264c9ceae -r 586195685aaf Misc/NEWS
--- a/Misc/NEWS	Tue Aug 18 13:26:57 2015 -0400
+++ b/Misc/NEWS	Tue Aug 18 14:30:15 2015 -0400
@@ -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
 ----