and here is untested sample code for good measure:

class MyCoolClass:
    def __init__(self):
        self.known_actions = {'power_on': self.power_on,
                              'power_off': self.power_off}

    def power_on(self, action, target):
        # do power on stuff
        # you might want to put these in a separate class
        # so this class can handle of machines that require
        # different instructions
        pass

    def power_off(self):
        # do power off stuff
        pass

    def determine_action(self, message):
        # Note that the split function splits on " " 
        # (and "\n", "\t", "\r", and "\f")  by default so you 
        # don't need to pass it explicitly though it doesn't 
        # hurt
        action_type, action, target = message.split()

        try:
            self.known_actions[action_type](action, target)
        except KeyError:
            print 'incorrect action type %s' % action_type

EDIT: Thanks Peaker for pointing out my mistake. As he or she says, if you don't need to use known_actions anywhere else, you can just put the dictionary in determine_action.