diff --git a/rest_framework/utils/encoders.py b/rest_framework/utils/encoders.py
index 7992b6b1c..174b08b8b 100644
--- a/rest_framework/utils/encoders.py
+++ b/rest_framework/utils/encoders.py
@@ -7,7 +7,6 @@ from django.db.models.query import QuerySet
 from django.utils.datastructures import SortedDict
 from django.utils.functional import Promise
 from rest_framework.compat import force_text
-# from rest_framework.serializers import DictWithMetadata, SortedDictWithMetadata
 import datetime
 import decimal
 import types
@@ -17,45 +16,47 @@ import json
 class JSONEncoder(json.JSONEncoder):
     """
     JSONEncoder subclass that knows how to encode date/time/timedelta,
-    decimal types, and generators.
+    decimal types, generators and other basic python objects.
     """
-    def default(self, o):
+    def default(self, obj):
         # For Date Time string spec, see ECMA 262
         # http://ecma-international.org/ecma-262/5.1/#sec-15.9.1.15
-        if isinstance(o, Promise):
-            return force_text(o)
-        elif isinstance(o, datetime.datetime):
-            r = o.isoformat()
-            if o.microsecond:
-                r = r[:23] + r[26:]
-            if r.endswith('+00:00'):
-                r = r[:-6] + 'Z'
-            return r
-        elif isinstance(o, datetime.date):
-            return o.isoformat()
-        elif isinstance(o, datetime.time):
-            if timezone and timezone.is_aware(o):
+        if isinstance(obj, Promise):
+            return force_text(obj)
+        elif isinstance(obj, datetime.datetime):
+            representation = obj.isoformat()
+            if obj.microsecond:
+                representation = representation[:23] + representation[26:]
+            if representation.endswith('+00:00'):
+                representation = representation[:-6] + 'Z'
+            return representation
+        elif isinstance(obj, datetime.date):
+            return obj.isoformat()
+        elif isinstance(obj, datetime.time):
+            if timezone and timezone.is_aware(obj):
                 raise ValueError("JSON can't represent timezone-aware times.")
-            r = o.isoformat()
-            if o.microsecond:
-                r = r[:12]
-            return r
-        elif isinstance(o, datetime.timedelta):
-            return str(o.total_seconds())
-        elif isinstance(o, decimal.Decimal):
-            return float(o)
-        elif isinstance(o, QuerySet):
-            return list(o)
-        elif hasattr(o, 'tolist'):
-            return o.tolist()
-        elif hasattr(o, '__getitem__'):
+            representation = obj.isoformat()
+            if obj.microsecond:
+                representation = representation[:12]
+            return representation
+        elif isinstance(obj, datetime.timedelta):
+            return str(obj.total_seconds())
+        elif isinstance(obj, decimal.Decimal):
+            # Serializers will coerce decimals to strings by default.
+            return float(obj)
+        elif isinstance(obj, QuerySet):
+            return list(obj)
+        elif hasattr(obj, 'tolist'):
+            # Numpy arrays and array scalars.
+            return obj.tolist()
+        elif hasattr(obj, '__getitem__'):
             try:
-                return dict(o)
+                return dict(obj)
             except:
                 pass
-        elif hasattr(o, '__iter__'):
-            return [i for i in o]
-        return super(JSONEncoder, self).default(o)
+        elif hasattr(obj, '__iter__'):
+            return [item for item in obj]
+        return super(JSONEncoder, self).default(obj)
 
 
 try: