python3: use BytesIO for response cache

combo/utils/requests_wrapper.py

@@ -16,7 +16,6 @@
 
 import hashlib
 import logging
-from StringIO import StringIO
 
 from requests import Response, Session as RequestsSession
 
@@ -25,6 +24,7 @@ from django.core.cache import cache
 from django.utils.encoding import smart_bytes
 from django.utils.http import urlencode
 from django.utils.six.moves.urllib.parse import urlparse, urlunparse
+from django.utils.six import BytesIO
 
 from .signature import sign_url
 
@@ -110,7 +110,7 @@ class Requests(RequestsSession):
             if cache_content and not invalidate_cache:
                 response = Response()
                 response.status_code = 200
-                response.raw = StringIO(cache_content)
+                response.raw = BytesIO(smart_bytes(cache_content))
                 return response
             elif raise_if_not_cached:
                 raise NothingInCacheException()