Fixed #15197 -- Fixed yaml serialization into HttpResponse

Thanks fourga38 for the report and hirokiky at gmail.com for the
initial patch.

django/core/serializers/json.py

@@ -52,9 +52,8 @@ class Serializer(PythonSerializer):
         self._current = None
 
     def getvalue(self):
-        # overwrite PythonSerializer.getvalue() with base Serializer.getvalue()
-        if callable(getattr(self.stream, 'getvalue', None)):
-            return self.stream.getvalue()
+        # Grand-parent super
+        return super(PythonSerializer, self).getvalue()
 
 
 def Deserializer(stream_or_string, **options):

django/core/serializers/pyyaml.py

@@ -44,7 +44,8 @@ class Serializer(PythonSerializer):
         yaml.dump(self.objects, self.stream, Dumper=DjangoSafeDumper, **self.options)
 
     def getvalue(self):
-        return self.stream.getvalue()
+        # Grand-parent super
+        return super(PythonSerializer, self).getvalue()
 
 def Deserializer(stream_or_string, **options):
     """

tests/regressiontests/serializers_regress/tests.py

@@ -21,6 +21,7 @@ from django.core import serializers
 from django.core.serializers import SerializerDoesNotExist
 from django.core.serializers.base import DeserializationError
 from django.db import connection, models
+from django.http import HttpResponse
 from django.test import TestCase
 from django.utils.functional import curry
 from django.utils.unittest import skipUnless
@@ -501,14 +502,17 @@ def streamTest(format, self):
     obj.save_base(raw=True)
 
     # Serialize the test database to a stream
-    stream = BytesIO()
+    for stream in (BytesIO(), HttpResponse()):
         serializers.serialize(format, [obj], indent=2, stream=stream)
 
         # Serialize normally for a comparison
         string_data = serializers.serialize(format, [obj], indent=2)
 
         # Check that the two are the same
+        if isinstance(stream, BytesIO):
             self.assertEqual(string_data, stream.getvalue())
+        else:
+            self.assertEqual(string_data, stream.content)
         stream.close()
 
 for format in serializers.get_serializer_formats():