get_excluded_fieldnames() should respect Meta options' ability to be either a tuple or list. Fixes #490.

Refactored `if self.opt.fields` out of the for loop.
Updated and cleaned up the validation-tests.

1 files changed, 3 insertions, 3 deletions

diff --git a/rest_framework/serializers.py b/rest_framework/serializers.py
index 7eab9860..c3f260c7 100644
--- a/rest_framework/serializers.py
+++ b/rest_framework/serializers.py
@@ -132,9 +132,9 @@ class BaseSerializer(Field):
         Returns the fieldnames that should not be validated.
         """
         excluded_fields = list(self.opts.exclude)
-        for field in self.fields.keys() + self.get_default_fields().keys():
-            if self.opts.fields:
-                if field not in self.opts.fields + self.opts.exclude:
+        if self.opts.fields:
+            for field in self.fields.keys() + self.get_default_fields().keys():
+                if field not in list(self.opts.fields) + excluded_fields:
                     excluded_fields.append(field)
         return excluded_fields