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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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