state_machine
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 state_machine.
Install
pip install state_machineBasic Usage
@acts_as_state_machine
class Person():
name = 'Billy'
sleeping = State(initial=True)
running = State()
cleaning = State()
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)
@before('sleep')
def do_one_thing(self):
print "{} is sleepy".format(self.name)
@before('sleep')
def do_another_thing(self):
print "{} is REALLY sleepy".format(self.name)
@after('sleep')
def snore(self):
print "Zzzzzzzzzzzz"
@after('sleep')
def big_snore(self):
print "Zzzzzzzzzzzzzzzzzzzzzz"
person = Person()
print person.current_state == Person.sleeping # True
print person.is_sleeping # True
print person.is_running # False
person.run()
print person.is_running # True
person.sleep()
# Billy is sleepy
# Billy is REALLY sleepy
# Zzzzzzzzzzzz
# Zzzzzzzzzzzzzzzzzzzzzz
print person.is_sleeping # TrueFeatures
Before / After Callback Decorators
You can add callback hooks that get executed before or after an event (see example above).
Important: if the before event causes an exception or returns
False, the state will not change (transition is blocked) and the
after event will not be executed.
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.
@acts_as_state_machine
class Person(mongoengine.Document):
name = mongoengine.StringField(default='Billy')
sleeping = State(initial=True)
running = State()
cleaning = State()
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)
@before('sleep')
def do_one_thing(self):
print "{} is sleepy".format(self.name)
@before('sleep')
def do_another_thing(self):
print "{} is REALLY sleepy".format(self.name)
@after('sleep')
def snore(self):
print "Zzzzzzzzzzzz"
@after('sleep')
def snore(self):
print "Zzzzzzzzzzzzzzzzzzzzzz"
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()
person2 = Person.objects(id=person.id).first()
assert person2.is_runningSqlalchemy
All you need to do is have sqlalchemy manage your object. For example:
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
@acts_as_state_machine
class Puppy(Base):
...Issues / Roadmap:
- Allow multiple state_machines per object
- Be able to configure the state field
Questions / Issues
Feel free to ping me on twitter: @tushman or add issues or PRs at https://github.com/jtushman/state_machine
Thank you
to aasm and ruby’s state_machine and all other state machines that I loved before
