Can't extend `bob.learn.linear.Machine`

Hi guys,

I'm bit rusted with respect to python bindings (it's not the kinda of development that you do in a daily basis). Basically I can't extend bob.learn.linear.Machine class and I can't understand why

import bob.learn.linear

class xuxa(bob.learn.linear.Machine):
    pass

Can someone shine a light on me?

Thanks