As discussed in https://bugs.python.org/issue23487, `action` works if the class is compatible with argparse._SubParsersAction.

these commands all do the same thing:

    parser.add_subparsers()       # default
    parser.add_subparsers(action='parsers')  
    parser.add_subparsers(action=argparse._SubParsersAction) 

Your example using 

    parser.add_subparsers(action='store')

raises the error because the argparse._StoreAction class cannot handle the `parser_class` parameter that add_subparsers has added to the kwargs.