improve doc

Doc/library/argparse.rst

@@ -803,7 +803,7 @@ how the command-line arguments should be handled. The supplied actions are:
 
     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument("--foo", action="extend", nargs="+", type=str)
-    >>> parser.parse_args("--foo f1 --foo f2 f3 f4".split())
+    >>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
     Namespace(foo=['f1', 'f2', 'f3', 'f4'])
 
 You may also specify an arbitrary action by passing an Action subclass or