code: def unregister(self, namespace, command=None):
          
          if not namespace:
              namespace = DEFAULT_NAMESPACE
  
          namespace = namespace.strip().lower()
          if namespace not in self._commands:
              self._logger.warning("Unknown name space: %s", namespace)
              return False
  
          if command is not None:
              # Remove the command
              command = command.strip().lower()
              if command not in self._commands[namespace]:
                  self._logger.warning(
                      "Unknown command: %s.%s", namespace, command
                  )
                  return False
  
              del self._commands[namespace][command]
  
              # Remove the name space if necessary
              if not self._commands[namespace]:
                  del self._commands[namespace]
          else:
              # Remove the whole name space
              del self._commands[namespace]
  
          return True
docs: Unregisters the given command. If command is None, the whole name space
          is unregistered.
  
          :param namespace: The command name space.
          :param command: The shell name of the command, or None
          :return: True if the command was known, else False