code: def theme_set(new):
      
      if (not isinstance(new, theme) and
              not issubclass(new, theme)):
          raise PlotnineError("Expecting object to be a theme")
  
      out = get_option('current_theme')
      set_option('current_theme', new)
      return out
docs: Change the current(default) theme
  
      Parameters
      ----------
      new : theme
          New default theme
  
      Returns
      -------
      out : theme
          Previous theme