code: def add_theme(self, other, inplace=False):
          
          if other.complete:
              return other
  
          theme_copy = self if inplace else deepcopy(self)
          theme_copy.themeables.update(deepcopy(other.themeables))
          return theme_copy
docs: Add themes together.
  
          Subclasses should not override this method.
  
          This will be called when adding two instances of class 'theme'
          together.
          A complete theme will annihilate any previous themes. Partial themes
          can be added together and can be added to a complete theme.