diff --git a/oauth2client/appengine.py b/oauth2client/appengine.py
index 1420279..b484c1e 100644
--- a/oauth2client/appengine.py
+++ b/oauth2client/appengine.py
@@ -448,7 +448,8 @@
 
     Args:
       filename: string, File name of client secrets.
-      scope: string, Space separated list of scopes.
+      scope: string or list of strings, scope(s) of the credentials being
+        requested.
       message: string, A friendly string to display to the user if the
         clientsecrets file is missing or invalid. The message may contain HTML and
         will be presented on the web interface for any method that uses the
@@ -479,7 +480,8 @@
 
   Args:
     filename: string, File name of client secrets.
-    scope: string, Space separated list of scopes.
+    scope: string or list of strings, scope(s) of the credentials being
+      requested.
     message: string, A friendly string to display to the user if the
       clientsecrets file is missing or invalid. The message may contain HTML and
       will be presented on the web interface for any method that uses the
diff --git a/oauth2client/client.py b/oauth2client/client.py
index 71c9d81..f6f4a1a 100644
--- a/oauth2client/client.py
+++ b/oauth2client/client.py
@@ -159,7 +159,8 @@
     t = type(self)
     d = copy.copy(self.__dict__)
     for member in strip:
-      del d[member]
+      if member in d:
+        del d[member]
     if 'token_expiry' in d and isinstance(d['token_expiry'], datetime.datetime):
       d['token_expiry'] = d['token_expiry'].strftime(EXPIRY_FORMAT)
     # Add in information we will need later to reconsistitue this instance.
@@ -203,6 +204,19 @@
     from_json = getattr(kls, 'from_json')
     return from_json(s)
 
+  @classmethod
+  def from_json(cls, s):
+    """Instantiate a Credentials object from a JSON description of it. The JSON
+    should have been produced by calling .to_json() on the object.
+
+    Args:
+      data: dict, A deserialized JSON object.
+
+    Returns:
+      An instance of a Credentials subclass.
+    """
+    return Credentials()
+
 
 class Flow(object):
   """Base class for all Flow objects."""