code: def from_class_name(name, theme_element):
          
          msg = "No such themeable element {}".format(name)
          try:
              klass = themeable._registry[name]
          except KeyError:
              raise PlotnineError(msg)
  
          if not issubclass(klass, themeable):
              raise PlotnineError(msg)
  
          return klass(theme_element)
docs: Create an themeable by name
  
          Parameters
          ----------
          name : str
              Class name
          theme_element : element object
              One of :class:`element_line`, :class:`element_rect`,
              :class:`element_text` or :class:`element_blank`
  
          Returns
          -------
          out : Themeable