A DocsClient singleton, used to look up spreadsheets
        by name.

def docs_client(self):
        """ A DocsClient singleton, used to look up spreadsheets
        by name. """
        if not hasattr(self, '_docs_client'):
            client = DocsClient()
            client.ClientLogin(self.google_user, self.google_password,
                               SOURCE_NAME)
            self._docs_client = client
        return self._docs_client