fixed a bug in serializers

djangorestframework/serializer.py

@@ -228,16 +228,16 @@ class Serializer(object):
 
         # serialize each required field 
         for fname in fields:
-            if fname in instance:
-                # finally check for a key 'fname' on the instance
-                obj = instance[fname]
-            elif hasattr(self, smart_str(fname)):
-                # check for a method 'fname' on self first
+            if hasattr(self, smart_str(fname)):
+                # check first for a method 'fname' on self first
                 meth = getattr(self, fname)
                 if inspect.ismethod(meth) and len(inspect.getargspec(meth)[0]) == 2:
                     obj = meth(instance)
+            elif hasattr(instance, '__contains__') and fname in instance:
+                # check for a key 'fname' on the instance
+                obj = instance[fname]
             elif hasattr(instance, smart_str(fname)):
-                # now check for an attribute 'fname' on the instance
+                # finally check for an attribute 'fname' on the instance
                 obj = getattr(instance, fname)
             else:
                 continue