code: def assign_did(self, did):
          
          if re.match('^#.*', self._id):
              self._id = did + self._id
          if re.match('^#.*', self._owner):
              self._owner = did + self._owner
docs: assign the DID as the key id, if the DID does not have a '#value'
          at the end, then automatically add a new key value