Using Timer or Scheduler in a Class

[Steven D'Aprano]

Hi Justin,

Does Professor Battersea know you're using his gmail account? *wink*


On Wed, 13 Aug 2008 23:16:12 -0400, Prof. William Battersea wrote:

> I'd like a class method to fire every n seconds.
> 
> I tried this:
> 
> class Timed:
>     def.__init__(self):
>         self.t = Timer(3, self.dothing)
 
>     def.start(self):
>         self.t.start()
> 
>     def.dothing(self):
>         print "Doing Thing"
> 
> s = new Timed()
> s.start()

This can't be your actual code, because "s = new Timed()" gives a 
SyntaxError. So does "def.start(self)" etc.

Also, what's Timer? 


> And:
> 
> class Scheduled:
>     def.__init__(self):
>         self.s = sched.scheduler(time.time, time.sleep) 
>         self.s.enter(3, 1, self.sync, ())
> 
>     def.start(self):
>         self.t.start()
> 
>     def.dothing(self):
>         print "Syncing"
> 
> s = new Scheduled()
> s.start()

When I fix the syntax errors and try to run the above code, I get this:

AttributeError: Scheduled instance has no attribute 'sync'

That's only the first of a number of errors. You waste our time when you 
post code that doesn't run. Very few people will bother spending the time 
and effort to fix your code if you don't respect their time, and those 
that do will rub your nose in the fact that you're wasting their time.


> Both run once and end. I'm obviously missing something here.

Let's start with some code that actually does run:

>>> class Scheduled:
...     def __init__(self):
...         self.s = sched.scheduler(time.time, time.sleep)
...         self.s.enter(3, 1, self.dothing, ())
...     def start(self):
...         self.s.run()
...         self.s.enter(3, 1, self.dothing, ())
...         self.start()
...     def dothing(self):
...         print "Syncing"
...
>>> s = Scheduled()
>>> s.start()
Syncing
Syncing
Syncing
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 8, in start
  File "<stdin>", line 8, in start
  File "<stdin>", line 8, in start
  File "<stdin>", line 6, in start
  File "/usr/lib/python2.5/sched.py", line 108, in run
    delayfunc(time - now)
KeyboardInterrupt

This will run until you interrupt it (as I did) or you run out of space 
on the stack due to recursion. I imagine this is probably not the best 
way to do what you want.

Hint for further explorations: the scheduler keeps a queue of events. If 
the queue becomes empty, it stops. You only need to restart the scheduler 
with run() if it stopped, otherwise it keeps going.



-- 
Steven