code: def add(self, private_key):
          
          if not isinstance(private_key, PaillierPrivateKey):
              raise TypeError("private_key should be of type PaillierPrivateKey, "
                              "not %s" % type(private_key))
          self.__keyring[private_key.public_key] = private_key
docs: Add a key to the keyring.
  
          Args:
            private_key (PaillierPrivateKey): a key to add to this keyring.