https://github.com/kyleconroy/statemachine

Simple finite-state machines in Python
https://github.com/kyleconroy/statemachine

Last synced: 3 months ago
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Simple finite-state machines in Python

• Host: GitHub
• URL: https://github.com/kyleconroy/statemachine
• Owner: kyleconroy
• License: mit
• Archived: true
• Created: 2012-04-26T07:17:55.000Z (about 12 years ago)
• Default Branch: master
• Last Pushed: 2012-04-26T20:25:21.000Z (about 12 years ago)
• Last Synced: 2024-03-19T12:48:19.135Z (3 months ago)
• Language: Python
• Homepage:
• Size: 130 KB
• Stars: 37
• Watchers: 6
• Forks: 6
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# `statemachine`

[![Build Status](https://secure.travis-ci.org/tnhu/jsface.png?branch=master)](http://travis-ci.org/tnhu/jsface)

If you aren't programming with state machines, [you should be](http://www.shopify.com/technology/3383012-why-developers-should-be-force-fed-state-machines).

`statemachine` offers a simple and easy-to-use finite-state machine that can adapted into almost any code base.

## Usage

To create a state machine, mix in the `statemachine.Machine` class. The only requirement is an initial state, which are represented as strings. 

```python

import statemachine

class TrafficLight(statemachine.Machine):

    initial_state = 'red'

```

This machine won't do much, but we can get the current state

```python

>>> stoplight = TrafficLight()

>>> stoplight.state

'red'

```

We can add state transitions using the `event` decorator. These functions return an iterable of transitions. A transition is just a two-tuple. The first element is an iterable of states, the wilcard '*', or a single state. The second element is the target state.

```python

import statemachine

class TrafficLight(statemachine.Machine):

    initial_state = 'red'

    @statemachine.event

    def cycle(self):

        yield 'red', 'green'

        yield 'green', 'yellow'

        yield 'yellow', 'red'

```

Calling the `cycle` method will transition the machine into the next state.

```python

>>> stoplight = TrafficLight()

>>> stoplight.state

'red'

>>> stoplight.cycle()

>>> stoplight.state

'green'

```

You can listen for transition events using the `before_transition` and `after_transition`  decorators`.

```python

import statemachine

class TrafficLight(statemachine.Machine):

    initial_state = 'red'

    @statemachine.event

    def cycle(self):

        yield 'red', 'green'

        yield 'green', 'yellow'

        yield 'yellow', 'red'

    @statemachine.after_transition('red', 'green')

    def announce(self):

        print "GO GO GO"

```

Initiate the transition by calling `cycle`

```python

>>> stoplight = TrafficLight()

>>> stoplight.cycle()

'GO GO GO'

```

If you only care about where you're coming from (or where you're going), use the `transition_from` and `transition_to` decorator

```python

import statemachine

class TrafficLight(statemachine.Machine):

    initial_state = 'red'

    @statemachine.event

    def cycle(self):

        yield 'red', 'green'

        yield 'green', 'yellow'

        yield 'yellow', 'red'

    @transition_to('yellow')

    def safety(self):

        print "SLOW DOWN"

    @transition_from('red')

    def announce(self):

        print "GO GO GO"

```

## Installation

    $ pip install statemachine