pysm

state machine for humans

There are two types of developers in this world: those who love state machines and those who will eventually.

I fall in the first camp. I think it is really important to have a declarative way to define the states of an object. That’s why I developed pysm.

Install

pip install pysm

Basic Usage

Features

Blocks invalid state transitions

An InvalidStateTransition Exception will be thrown if you try to move into an invalid state.

ORM support

We have basic support for mongoengine, and sqlalchemy.

Mongoengine

Just have your object inherit from mongoengine.Document and state_machine will add a StringField for state.

Note: You must explicitly call #save to persist the document to the datastore.

@pysm.state_machine
class Person(mongoengine.Document):

    name = mongoengine.StringField(default='Billy')

    class Sleeping(pysm.State):

        initial = True

        def enter_state(self, from_state):
            pass

        def exit_state(self, to_state):
            pass

    class Running(pysm.State):

        def enter_state(self, from_state):
            pass

        def exit_state(self, to_state):
            pass

    class Cleaning(pysm.State):

        def enter_state(self, from_state):
            pass

        def exit_state(self, to_state):
            pass

    run = Event(from_states=Sleeping, to_state=Running)
    cleanup = Event(from_states=Running, to_state=Cleaning)
    sleep = Event(from_states=(Running, Cleaning), to_state=Sleeping)


person = Person()
person.save()
eq_(person.current_state, Person.Sleeping)
assert person.is_sleeping
assert not person.is_running
person.run()
assert person.is_running
person.sleep()
assert person.is_sleeping
person.run()
person.save()

Sqlalchemy

All you need to do is have sqlalchemy manage your object. For example:

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
@pysm.state_machine
class Puppy(Base):
   ...

Thank you

to aasm and ruby’s state_machine and jtushman's jtushman/state_machine and all other state machines that I loved before