a simple python state machine

stateMachine.py

class StateMachine(object):
    """the brain - manages states"""
    def __init__(self):
        self.states = {}
        self.active_state = None

    def add_state(self, state):
        """Adds a new state"""
        self.states[state.name] = state

    def think(self):
        """
        Does whatever the current state instructs
        and changes to new state if needed.
        """
        if self.active_state is not None:
            self.active_state.do_actions()
        new_state_name = self.active_state.check_conditions()
        if new_state_name is not None:
            self.set_state(new_state_name)

    def set_state(self, new_state_name):
        """Changes states and performs appropriate exit and entry actions."""
        if self.active_state is not None:
            self.active_state.exit_actions()
        self.active_state = self.states[new_state_name]
        self.active_state.__entry_actions__()


class State(object):
    """An abstract state."""
    def __init__(self, name):
        self.name = name

    def __entry_actions__(self):
        """Perform these actions when this state is first entered."""
        self.entry_actions()

    def do_actions(self):
        """Perform these actions when in this state."""
        pass

    def check_conditions(self):
        """Check these conditions to see if state should be changed."""
        pass

    def entry_actions(self):
        """Perform these actions when this state is first entered."""
        pass

    def exit_actions(self):
        """Perform these actions when this state is exited."""
        pass