Deterministic, Finite State Machine

Contents

• Installation
• State Machine
• • blueprint
• • state
• • context
• • initial
• • accepted
• • final
• Usage

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Installation

python setyp.py install

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StateMachine

Members

blueprint

This is a propery with a getter and setter that defines the state machine. Setting the blueprint will also reset the state machine.

{
    "initialState": state,
    "initialContext": dict(),
    "alphabet": set(),
    "validStates": set(),
    "acceptedStates": set(),
    "finalStates": set(),
    "transition": lambda state, context, event: new_state,
    "lifecycles": dict()
}

Initial Context

An optional dictionary, which can be used to share information between states and updated during state transitions.

Alphabet

A set of events, which are used to drive state transitions.

Initial State

The starting state. Must be a valid state.

Valid States

A set of valid states.

Accepted States

A set of accepted states.

Final States

A set of final states, once reached, new transitions will raise StopMachine.

Transition

A function, which takes state, context and event as parameters and returns the next state. The event must be a member of the alphabet and the new state must be a valid state.

Lifecycles

Lifecycle actions can be ran before or after specific events.

Events

A set of events, which are used to drive lifecycle actions.

Actions

A list of functions, which take state, context and event as parameters.

{
    "lifecycles": {
        "before": [{
            "events": {0, 1, 2, 3},
            "actions": [before_any]
        }],
        "after": [{
            events: {3},
            "actions": [after_three]
        }, {
            "events": {2, 3},
            "actions": [action1, action2]
        }]
    }
}

• before_any executes before events 0, 1, 2 & 3 transitions are executed
• after_three executres after event 3 transition is executed
• action1, then action2 executes after events 2 & 3 transitions are executed

state

The current state of the state machine.

context

The current context of the state machine.

initial

True or False if the current state is the initial state.

accepted

True or False if the current state is an accepted state.

final

True or False if the current state is a final state.

Methods

reset()

Resets the state machine's state and context to their initial values defined in the blueprint. The initial state must be a valid state.

• ValueError - Invalid initial state

set_state(state, context)

Set the state machine's state and context. The state must be a valid state.

• ValueError - Invalid state

transition(event)

Transitions the state machine to the next state by executing the transition defined in the blueprint. The event must be a valid member of the alphabet defined in the blueprint. The state must be a valid state.

• StopMachine - Current state is final
• ValueError - Invalid event

is_initial(state) -> True | False

is_valid(state) -> True | False

is_accepted(state) -> True | False

is_final(state) -> True | False

is_event(event) -> True | False

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Usage

Create a state machine with a blueprint and transition from the initial state 1 to accepted, final state 2.

from dfsmpy import StateMachine

machine = StateMachine({
    "alphabet": {1, 2},
    "initialState": 1,
    "validStates": {1, 2},
    "acceptedStates": {2},
    "finalStates": {2},
    "transition": lambda a, c, e: e
})

machine.transition(2)