fix add_metaclass when __slots__ is a string (fixes #47)

3 files changed, 20 insertions, 2 deletions

diff --git a/CHANGES b/CHANGES
index 19d3843..6aca0dd 100644
--- a/CHANGES
+++ b/CHANGES
@@ -6,6 +6,9 @@ This file lists the changes in each six version.
 Development version
 -------------------
 
+- Issue #47: Fix add_metaclass on classes with a string for the __slots__
+  variable.
+
 - Issue #44: Fix interpretation of backslashes on Python 2 in the u() function.
 
 - Pull request #21: Add import mapping for urllib's proxy_bypass function.
diff --git a/six.py b/six.py
index f782f9a..a0eea9a 100644
--- a/six.py
+++ b/six.py
@@ -581,7 +581,11 @@ def add_metaclass(metaclass):
         orig_vars = cls.__dict__.copy()
         orig_vars.pop('__dict__', None)
         orig_vars.pop('__weakref__', None)
-        for slots_var in orig_vars.get('__slots__', ()):
-            orig_vars.pop(slots_var)
+        slots = orig_vars.get('__slots__')
+        if slots is not None:
+            if isinstance(slots, str):
+                slots = [slots]
+            for slots_var in slots:
+                orig_vars.pop(slots_var)
         return metaclass(cls.__name__, cls.__bases__, orig_vars)
     return wrapper
diff --git a/test_six.py b/test_six.py
index 81b424f..7f92617 100644
--- a/test_six.py
+++ b/test_six.py
@@ -630,3 +630,14 @@ def test_add_metaclass():
     instance = MySlots()
     instance.a = "foo"
     py.test.raises(AttributeError, setattr, instance, "c", "baz")
+
+    # Test a class with string for slots.
+    class MyStringSlots(object):
+        __slots__ = "ab"
+    MyStringSlots = six.add_metaclass(Meta1)(MyStringSlots)
+    assert MyStringSlots.__slots__ == "ab"
+    instance = MyStringSlots()
+    instance.ab = "foo"
+    py.test.raises(AttributeError, setattr, instance, "a", "baz")
+    py.test.raises(AttributeError, setattr, instance, "b", "baz")
+