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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 client_auth(self):
 """Generate an XML element with client auth data populated."""

        if not self._client_auth:
            self._client_auth = E.Element('merchantAuthentication')
            E.SubElement(self._client_auth, 'name').text = self.config.login_id
            E.SubElement(self._client_auth, 'transactionKey').text = self.config.transaction_key
        return self._client_auth