code: def get_obsolete_messages(self, domain):
          
          if domain not in self.domains:
              raise ValueError('Invalid domain: {0}'.format(domain))
  
          if domain not in self.messages or \
              'obsolete' not in self.messages[domain]:
              self._process_domain(domain)
  
          return self.messages[domain]['obsolete']
docs: Returns obsolete valid messages after operation.
          @type domain: str
          @rtype: dict