I need help building a data structure for a state diagram

[Paul McGuire]

On May 24, 1:16 pm, Matthew Wilson <m... at tplus1.com> wrote:
> I'm working on a really simple workflow for my bug tracker.  I want
> filed bugs to start in an UNSTARTED status.  From there, they can go to
> STARTED.
>

I just wrote an article for the April issue of Python Magazine on how
to add embedded DSL code to your Python scripts using Python's imputil
module, and I used a state pattern for my example.  Two state machine
examples I used to illustrate the work were a traffic light and a
library book checkin/checkout.  The traffic light state machine is
just a simple cycle through the 3 light states.  But the library book
state machine is more complex (your bug tracking example made me think
of it), with different transitions allowed one state into multiple
different states.  Here is how the code looks for these examples:

==============
# trafficLight.pystate
statemachine TrafficLight:
    Red -> Green
    Green -> Yellow
    Yellow -> Red

Red.carsCanGo    = False
Yellow.carsCanGo = True
Green.carsCanGo  = True

# ... other class definitions for state-specific behavior ...

==============
# trafficLightDemo.py

# add support for .pystate files, with
# embedded state machine DSL
import stateMachine

import trafficLight

tlight = trafficLight.Red()
while 1:
    print tlight, "GO" if tlight.carsCanGo else "STOP"
    tlight.delay()
    tlight = tlight.next_state()


==============
# libraryBook.pystate

statemachine BookCheckout:
    New       -(create)->   Available
    Available -(reserve)->  Reserved
    Available -(checkout)-> CheckedOut
    Reserved  -(cancel)->   Available
    Reserved  -(checkout)-> CheckedOut
    CheckedOut -(checkin)->  Available
    CheckedOut -(renew)->   CheckedOut


You don't need to adopt this whole DSL implementation, but the article
might give you some other ideas.

-- Paul