A simple, stupid (as in KISS) state maschine

StateMachine.py

class InvalidStateException(Exception):
    pass

class MissingStateMachineConfigurationException(Exception):
    pass


from types import DictionaryType

class StateMachine(object):
    def __init__(self, configuration, logger):
        '''
        Example of a valid state machine configuration:
            state_machine_configuration =\
                {
                    '<current_state>' :
                                {
                                    '<transition_event>' : '<next_state_to_enter>',
                                },
                    <another_current_state> ...
                }

        Where each state is a method that executes the code/action(s) associated with that state. Inside the method
        an expression:
            own_method_name = inspect.stack()[0][3]
        could be used to capture the method name aka state name. Then the *last* statement of that method must be:
            # do transition to configured state
            return getattr(self, self.sm.sm(own_method_name, event))()
        '''
        if (type(configuration) == DictionaryType) and (len(configuration) != 0):
            self.configuration = configuration
        else:
            raise MissingStateMachineConfigurationException(
                "Missing required State Machine configuration (dict required)!")
        self.log = logger

    def sm(self, current_state, event):
        try:
            next_state = self.configuration[current_state][event]
            self.log.debug(">>  sm: %s --- %s --> %s" % (current_state, event, next_state))
            return next_state
        except KeyError:
            missing_key_tuple = (current_state, event)
            raise InvalidStateException("Unknown state! Missing key tuple was: '(%s,%s)'" %
                                            (missing_key_tuple[0],missing_key_tuple[1]))