Restored 2.5 compatibility and actual fix for the json problem

flask/helpers.py

@@ -19,6 +19,7 @@ from zlib import adler32
 # try to load the best simplejson implementation available.  If JSON
 # is not installed, we add a failing class.
 json_available = True
+json = None
 try:
     import simplejson as json
 except ImportError:
@@ -32,7 +33,6 @@ from werkzeug import Headers, wrap_file, is_resource_modified, cached_property
 from jinja2 import FileSystemLoader
 
 from .globals import session, _request_ctx_stack, current_app, request
-from .wrappers import Response
 
 
 def _assert_have_json():
@@ -364,3 +364,7 @@ class _PackageBoundObject(object):
                          subfolders use forward slashes as separator.
         """
         return open(os.path.join(self.root_path, resource), 'rb')
+
+
+# circular dependencies between wrappers and helpers
+from .wrappers import Response