.. efun:: string set_prompt(mixed prompt, object ob)

  Set the prompt given by the first argument for the interactive object instead of the default prompt. If the second argument is omitted, ``this_player()`` is used as default. The first arg can be a string or a closure.

  The result returned is the old prompt.

  If the first arg is the number 0, the prompt is not changed, just returned.

  .. seealso:: :overview:`hook`