importing modules in python

i am having some trouble in understanding how to distribute a tornado application into multiple files.i need to have one file which creates the application instance another file which handles login/logout functionality ,another which handles profile page view and so on.but what i dont get is how to do this . lets say for example i have two files: -app.py(creating app instance) -auth.py(login/logout functionality)

app.py
>import tornado
>import auth
> handlers = [
            (r"/", MainHandler),
            (r"/auth", auth.AuthHandler),
            (r"/logout", auth.LogoutHandler),
        ]

this works fine but when i have app.py as this:

>import tornado
>import auth
>import profile
> handlers = [
            (r"/", MainHandler),
            (r"/auth", auth.AuthHandler),
            (r"/logout", auth.LogoutHandler),
            (r"/profile", profile.ViewHandler),
        ]

auth.py
>import tornado
>import app
>class AuthHandler(app.BaseHandler)
> > ...
>class LogoutHandler(app.BaseHandler)
> >...

and in profile.py i have this:
>import app
>import tornado开发者_开发技巧
>class ViewProfile(app.BaseHandler)
---it shows error that in profile.py module app has no attribute BaseHandler

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What happens if you drop the "import app" in both auth.py and profile.py? it seems you are creating circular imports.