Work around 2.x/3.x json.dumps() return type fuzziness

rest_framework/fields.py

@@ -1544,7 +1544,11 @@ class JSONField(Field):
 
     def to_representation(self, value):
         if self.binary:
-            return json.dumps(value)
+            value = json.dumps(value)
+            # On python 2.x the return type for json.dumps() is underspecified.
+            # On python 3.x json.dumps() returns unicode strings.
+            if isinstance(value, six.text_type):
+                value = bytes(value.encode('utf-8'))
         return value
 
 

tests/test_fields.py

@@ -1562,7 +1562,7 @@ class TestBinaryJSONField(FieldValues):
     Values for `JSONField` with binary=True.
     """
     valid_inputs = [
-        ('{"a": 1, "3": null, "b": ["some", "list", true, 1.23]}', {
+        (b'{"a": 1, "3": null, "b": ["some", "list", true, 1.23]}', {
             'a': 1,
             'b': ['some', 'list', True, 1.23],
             '3': None
@@ -1576,7 +1576,7 @@ class TestBinaryJSONField(FieldValues):
             'a': 1,
             'b': ['some', 'list', True, 1.23],
             '3': None
-        }, '{"a": 1, "3": null, "b": ["some", "list", true, 1.23]}'),
+        }, b'{"a": 1, "3": null, "b": ["some", "list", true, 1.23]}'),
     ]
     field = serializers.JSONField(binary=True)