Fix _resolve_model to work with unicode strings

rest_framework/serializers.py

@@ -49,7 +49,7 @@ def _resolve_model(obj):
     String representations should have the format:
         'appname.ModelName'
     """
-    if type(obj) == str and len(obj.split('.')) == 2:
+    if isinstance(obj, six.string_types) and len(obj.split('.')) == 2:
         app_name, model_name = obj.split('.')
         return models.get_model(app_name, model_name)
     elif inspect.isclass(obj) and issubclass(obj, models.Model):

rest_framework/tests/test_serializers.py

@@ -3,6 +3,7 @@ from django.test import TestCase
 
 from rest_framework.serializers import _resolve_model
 from rest_framework.tests.models import BasicModel
+from rest_framework.compat import six
 
 
 class ResolveModelTests(TestCase):
@@ -19,6 +20,10 @@ class ResolveModelTests(TestCase):
         resolved_model = _resolve_model('tests.BasicModel')
         self.assertEqual(resolved_model, BasicModel)
 
+    def test_resolve_unicode_representation(self):
+        resolved_model = _resolve_model(six.text_type('tests.BasicModel'))
+        self.assertEqual(resolved_model, BasicModel)
+
     def test_resolve_non_django_model(self):
         with self.assertRaises(ValueError):
             _resolve_model(TestCase)