state machine and a global variable

[tuom.larsen at gmail.com]

On Dec 14, 11:06 pm, Bruno Desthuilliers
<bdesth.quelquech... at free.quelquepart.fr> wrote:
> tuom.lar... at gmail.com a écrit :
>
> > Dear list,
> > I'm writing very simple state machine library, like this:
>
> > _state = None
>
> > def set_state(state):
> >     global _state
> >     _state = state
>
> > def get_state():
> >     print _surface
>
> NameError here !-)
>
>
>
> > but I hate to use global variable.
>
> <aol />
>
> > So, please, is there a better way
> > of doing this? All I want is that a user has to type as little as
> > possible, like:
>
> > from state_machine import *
> > set_state(3)
> > get_state()
>
> > I.e., nothing like:
> > import state_machine
> > my_machine = state_machine.new_machine()
> > my_machine.set_state(3)
> > my_machine.get_state()
>
> A possible solution:
>
> # state_machine.py
> class _StateMachine(object):
>    def __init__(self):
>      self._state = SomethingHere()
>    def get_state(self):
>      return self._state
>    def set_state(self, xxx):
>      # etc
>
> _s = _StateMachine()
> get_state = _s.get_state()
> set_state = _s.set_state()
>

I guess you meant without the parentheses:
get_state = _s.get_state
set_state = _s.set_state


> You still have a global, but at least it's a machine instance, not it's
> state !-)
>
> Now the question is: why do you think it's so important for your users
> to only see functions ? What's so wrong with:
>
> from state_machine import *
> m = get_state_machine()
> m.set_state(42)

Well, I guess I can see the advantages of using the class instances
but ... um ... the world isn't like that! :)

Consider this: how do you add up some numbers?
- "My sum is zero."
- "I add 3 to my sum."
- "I add 2 to my sum."

Or:
- "Three."
- "plus two."

Implicit context, some people call it. Sometimes it's useful to be as
precise as possible ("explicit is better than implict", right?) but
sometimes, it seems to me, it's just more natural not to repeat the
context all over again.

Thoughts?