code: def add_argument_group(self, title, description=None):
          
          try:
              groups = self.__groups
          except AttributeError:
              groups = self.__groups = {}
  
          if title not in groups:
              groups[title] = super().add_argument_group(
                  title=title, description=description)
  
          return groups[title]
docs: Add an argument group, or return a pre-existing one.