workaround missing dictproxy methods Fixes benjaminp#295

six.py

@@ -609,11 +609,21 @@ def iteritems(d, **kw):
     def iterlists(d, **kw):
         return d.iterlists(**kw)
 
-    viewkeys = operator.methodcaller("viewkeys")
+    def viewkeys(d):
+        if isinstance(d, types.DictProxyType):
+            d = dict(d)
+        return d.viewkeys()
 
-    viewvalues = operator.methodcaller("viewvalues")
+    def viewvalues(d):
+        if isinstance(d, types.DictProxyType):
+            d = dict(d)
+        return d.viewvalues()
+
+    def viewitems(d):
+        if isinstance(d, types.DictProxyType):
+            d = dict(d)
+        return d.viewitems()
 
-    viewitems = operator.methodcaller("viewitems")
 
 _add_doc(iterkeys, "Return an iterator over the keys of a dictionary.")
 _add_doc(itervalues, "Return an iterator over the values of a dictionary.")