<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def do_identity(args):
 """Executes the config commands subcommands. """

    if args.subcommand == 'policy' and args.policy_cmd == 'create':
        _do_identity_policy_create(args)
    elif args.subcommand == 'policy' and args.policy_cmd == 'list':
        _do_identity_policy_list(args)
    elif args.subcommand == 'role' and args.role_cmd == 'create':
        _do_identity_role_create(args)
    elif args.subcommand == 'role' and args.role_cmd == 'list':
        _do_identity_role_list(args)
    else:
        raise AssertionError(
            '"{}" is not a valid subcommand of "identity"'.format(
                args.subcommand))