code: def _expand_space(self):
          
  
          ## --- Expand the config space
          self._expand_config_space()
  
          ## --- Expand the space
          self.space_expanded = []
          for variable in self.space:
              self.space_expanded += variable.expand()
docs: Creates an internal list where the variables with dimensionality larger than one are expanded.
          This list is the one that is used internally to do the optimization.