学习python艰难的方式练习52

Question

我对练习52中的代码感到困惑。

if session.room and form.action:
    session.room = session.room.go(form.action)

我突出了代码。我不知道为什么它需要这个以及为什么如果我删除它们就无法通过测试。

import web
from gothonweb import map

urls = (
  '/game', 'GameEngine',
  '/', 'Index',
)

app = web.application(urls, globals())

# little hack so that debug mode works with sessions
if web.config.get('_session') is None:
    store = web.session.DiskStore('sessions')
    session = web.session.Session(app, store,
                                  initializer={'room': None})
    web.config._session = session
else:
    session = web.config._session

render = web.template.render('templates/', base="layout")


class Index(object):
    def GET(self):
        # this is used to "setup" the session with starting values
        session.room = map.START
        web.seeother("/game")


class GameEngine(object):

    def GET(self):
        if session.room:
            return render.show_room(room=session.room)
        else:
            # why is there here? do you need it?
            return render.you_died()

    def POST(self):
        form = web.input(action="None")

        # there is a bug here, can you fix it?
        if session.room and form.action:
            session.room = session.room.go(form.action)

        web.seeother("/game")



if __name__ == "__main__":
    app.run()