code: def get_assertion_id(self):
          
          if not self.validate_num_assertions():
              raise OneLogin_Saml2_ValidationError(
                  'SAML Response must contain 1 assertion',
                  OneLogin_Saml2_ValidationError.WRONG_NUMBER_OF_ASSERTIONS
              )
          return self.__query_assertion('')[0].get('ID', None)
docs: :returns: the ID of the assertion in the response
          :rtype: string