Finite State Machine

Lightweight, decorator-based Python implementation of a Finite State Machine.

Installation

pip install finite-state-machine

Usage

You will need to subclass StateMachine and set the state instance variable.

The transition decorator can be used to specify valid transitions.

See examples for sample State Machine workflows.

Example

from finite_state_machine import StateMachine, transition

class Turnstile(StateMachine):
    initial_state = "close"

    def __init__(self):
        self.state = self.initial_state
        super().__init__()

    @transition(source=["close", "open"], target="open")
    def insert_coin(self):
        pass

    @transition(source="open", target="close")
    def pass_thru(self):
        pass

REPL

In [2]: turnstile = Turnstile()

In [3]: turnstile.state
Out[3]: 'close'

In [4]: turnstile.insert_coin()

In [5]: turnstile.state
Out[5]: 'open'

In [6]: turnstile.insert_coin()

In [7]: turnstile.state
Out[7]: 'open'

In [8]: turnstile.pass_thru()

In [9]: turnstile.state
Out[9]: 'close'

In [10]: turnstile.pass_thru()
---------------------------------------------------------------------------
InvalidStartState                         Traceback (most recent call last)
<ipython-input-10-6abc6f4be1cd> in <module>
----> 1 turnstile.pass_thru()

~/state_machine.py in _wrapper(*args, **kwargs)
     32
     33             if self.state not in source:
---> 34                 raise InvalidStartState
     35
     36             for condition in conditions:

InvalidStartState:

Contributing

1. Clone repo
2. Create a virtual environment
3. pip install -r requirements_dev.txt
4. Install pre-commit
5. Set up pre-commit hooks in repo: pre-commit install

Running Tests

pytest

Release

Use SemVer for versioning strategy

Instructions

1. Grab last version, X.Y.Z
2. Generate changelog: python scripts/generate_changelog.py -v X.Y.Z
3. Cut a release on GitHub
4. Upload to PyPI with flit

Flit Workflow

pip install flit
flit build --format sdist
flit publish --repository testpypi

Inspiration

This project is inspired by django-fsm. Wanted a decorator-based state machine without having to use Django.