'Retrieve the credentials from the dictionary, if they exist.
Returns: A :class:`oauth2client.client.OAuth2Credentials` instance.'

def locked_get(self):

    serialized = self._dictionary.get(self._key)
    if (serialized is None):
        return None
    credentials = client.OAuth2Credentials.from_json(serialized)
    credentials.set_store(self)
    return credentials
