Fluidity: state machine implementation for Python objects
State machine implementation for Python objects.
A very simple example taken from specs:
from fluidity import StateMachine, state, transition class SimpleMachine(StateMachine): initial_state = 'created' state('created') state('waiting') state('processed') state('canceled') transition(from_='created', event='queue', to='waiting') transition(from_='waiting', event='process', to='processed') transition(from_=['waiting', 'created'], event='cancel', to='canceled')
For demonstrating more advanced capabilities, a “slightly more complex example” from AASM, the Ruby’s most popular state machine implementation, is reproduced below, using Fluidity:
from fluidity import StateMachine, state, transition class Relationship(StateMachine): initial_state = lambda relationship: relationship.strictly_for_fun() and 'intimate' or 'dating' state('dating', enter='make_happy', exit='make_depressed') state('intimate', enter='make_very_happy', exit='never_speak_again') state('married', enter='give_up_intimacy', exit='buy_exotic_car_and_buy_a_combover') transition(from_='dating', event='get_intimate', to='intimate', guard='drunk') transition(from_=['dating', 'intimate'], event='get_married', to='married', guard='willing_to_give_up_manhood') def strictly_for_fun(self): pass def drunk(self): pass def willing_to_give_up_manhood(self): return True def make_happy(self): pass def make_depressed(self): pass def make_very_happy(self): pass def never_speak_again(self): pass def give_up_intimacy(self): pass def buy_exotic_car_and_buy_a_combover(self): pass
A Fluidity state machine must have one initial state and at least two states.
A state may have enter and exit callbacks, for running some code on state enter and exit, respectively. These params can be method names (as strings), callables, or lists of method names or callables.
Transitions lead the machine from a state to another. Transitions must have from_, to, and action parameters. from_ is one or more (as list) states from which the transition can be started. to is the state to which the transition will lead the machine. event is the method that have to be called to launch the transition. This method is automatically created by the Fluidity engine.
A transition can have optional action and guard parameters. action is a method (or callable) that will be called when transition is launched. If parameters are passed to the event method, they are passed to the action method, if it accepts these parameters. guard is a method (or callable) that is called to allow or deny the transition, depending on the result of its execution. Both “action” and guard can be lists.
The same event can be in multiple transitions, going to different states, having their respective guards as selectors. For the transitions having the same event, only one guard should return a true value at a time.
States and transitions are defined in a class-wide mode. However, one can define states and transitions for individual objects. For example, having “door” as a state machine:
door.add_state('broken') door.add_transition(from_='closed', event='crack', to='broken')
These additions only affect the target object.
pip install fluidity-sm
Note: the Pypi package is called fluidity-sm, not fluidity.