code: def updateSigner(self, identifier, signer):
          
          if identifier != signer.identifier:
              raise ValueError("Passed signer has identifier {} but it should"
                               " have been {}".format(signer.identifier,
                                                      identifier))
          if identifier not in self.idsToSigners:
              raise KeyError("Identifier {} not present in wallet".
                             format(identifier))
  
          oldSigner = self.idsToSigners[identifier]
          if oldSigner.alias and oldSigner.alias in self.aliasesToIds:
              logger.debug('Changing alias of passed signer to {}'.
                           format(oldSigner.alias))
              signer.alias = oldSigner.alias
  
          self.idsToSigners[identifier] = signer
docs: Update signer for an already present identifier. The passed signer
          should have the same identifier as `identifier` or an error is raised.
          Also if the existing identifier has an alias in the wallet then the
          passed signer is given the same alias
          :param identifier: existing identifier in the wallet
          :param signer: new signer to update too
          :return: