Fix issue #1231: JSONEncoder doesn't handle dict-like objects

Check for __getitem__ and then attempt to convert to a dict.
The check for __getitem__ is there as there's no universal way to
check if an object is a mapping type, but this is a likely proxy

rest_framework/tests/test_renderers.py

@@ -18,6 +18,9 @@ from rest_framework.test import APIRequestFactory
 import datetime
 import pickle
 import re
+import UserDict
+import collections
+import json
 
 
 DUMMYSTATUS = status.HTTP_200_OK
@@ -244,6 +247,60 @@ class JSONRendererTests(TestCase):
         ret = JSONRenderer().render(_('test'))
         self.assertEqual(ret, b'"test"')
 
+    def test_render_userdict_obj(self):
+        class DictLike(UserDict.DictMixin):
+            def __init__(self):
+                self._dict = dict()
+            def __getitem__(self, key):
+                return self._dict.__getitem__(key)
+            def __setitem__(self, key, value):
+                return self._dict.__setitem__(key, value)
+            def __delitem__(self, key):
+                return self._dict.__delitem__(key)
+            def keys(self):
+                return self._dict.keys()
+        x = DictLike()
+        x['a'] = 1
+        x['b'] = "string value"
+        ret = JSONRenderer().render(x)
+        self.assertEquals(json.loads(ret), {u'a': 1, u'b': u'string value'})
+
+    def test_render_dict_abc_obj(self):
+        class Dict(collections.MutableMapping):
+            def __init__(self):
+                self._dict = dict()
+            def __getitem__(self, key):
+                return self._dict.__getitem__(key)
+            def __setitem__(self, key, value):
+                return self._dict.__setitem__(key, value)
+            def __delitem__(self, key):
+                return self._dict.__delitem__(key)
+            def __iter__(self):
+                return self._dict.__iter__()
+            def __len__(self):
+                return self._dict.__len__()
+
+        x = Dict()
+        x['key'] = 'string value'
+        x[2] = 3
+        ret = JSONRenderer().render(x)
+        self.assertEquals(json.loads(ret), {u'key': 'string value', u'2': 3})
+            
+
+    def test_render_obj_with_getitem(self):
+        class DictLike(object):
+            def __init__(self):
+                self._dict = {}
+            def set(self, value):
+                self._dict = dict(value)
+            def __getitem__(self, key):
+                return self._dict[key]
+            
+        x = DictLike()
+        x.set({'a': 1, 'b': 'string'})
+        with self.assertRaises(TypeError):
+            JSONRenderer().render(x)
+        
     def test_without_content_type_args(self):
         """
         Test basic JSON rendering.

rest_framework/utils/encoders.py

@@ -44,6 +44,12 @@ class JSONEncoder(json.JSONEncoder):
             return str(o)
         elif hasattr(o, 'tolist'):
             return o.tolist()
+        elif hasattr(o, '__getitem__'):
+            try:
+                return dict(o)
+            except KeyError:
+                # Couldn't convert to a dict, fall through
+                pass
         elif hasattr(o, '__iter__'):
             return [i for i in o]
         return super(JSONEncoder, self).default(o)