FSM Workflow

Finite state machine workflows is the declarative way to describe consecutive operation through set of states and transitions between them.

viewflow.fsm can help you manage rules and restrictions around moving from one state to another. The package could be used to get low level db-independent fsm implementation, or to wrap existing database model, and implement simple persistent workflow process with quickly bootstrapped UI.

Quick start

All things are buit around viewflow.fsm.State. It is the special class slot, that can take a value only from a specific python enum or django enumeration type and that value can’t be changed with simple assignement.

from enum import Enum
from viewflow.fsm import State

class Stage(Enum):
   NEW = 1
   DONE = 2
   HIDDEN = 3

class MyFlow(object):
   stage = State(Stage, default=Stage.NEW)

   @stage.transition(source=Stage.NEW, target=Stage.DONE)
   def complete():

   @stage.transition(source=State.ANY, target=Stage.HIDDEN)
   def hide():

flow = MyFlow()
flow.stage == Stage.NEW  # True
flow.stage = Stage.DONE  # Raises AttributeError

flow.stage == Stage.DONE  # True

flow.complete()  # Now raises TransitionNotAllowed

Finite state machine could be seen as sort of dynamic typing. The transition() decorator augments the code with runtime checks to prevent methods to be executed in a wrong order.