code: def get_quantity(self, twig=None, unit=None,
                       default=None, t=None, **kwargs):
          
          # TODO: for time derivatives will need to use t instead of time (time
          # gets passed to twig filtering)
  
          if default is not None is not None:
              # then we need to do a filter first to see if parameter exists
              if not len(self.filter(twig=twig, **kwargs)):
                  return default
  
          param = self.get_parameter(twig=twig, **kwargs)
  
          if param.qualifier in kwargs.keys():
              # then we have an "override" value that was passed, and we should
              # just return that.
              # Example b.get_value('teff', teff=6000) returns 6000
              return kwargs.get(param.qualifier)
  
          return param.get_quantity(unit=unit, t=t)
docs: TODO: add documentation