wait until change

[Anand Pillai]

I thought this was fairly straightforward, but when
I tried to write one I figured out that the standard
python Timers cannot be used.

Anyway here is how you would go about doing it.
This piece of code uses a time out as an exit condition,
whereas in the scenario given by the O.P it would be
the file's timestamp verification.

----------------------------------------------------
from threading import Thread
import time

class ModifiedTimer(Thread):
    """ Modified timer with a maximum timeout 
        and repeated calls """

    def __init__(self, interval, maxtime, target):
        self.__interval = interval
        self.__maxtime = maxtime
        self.__tottime = 0.0
        self.__target = target
        self.__flag = 0
        Thread.__init__(self, None, 'mytimer', None)
        
    def run(self):

        while self.__flag==0:
            time.sleep(self.__interval)
            self.__target()
            self.__tottime += self.__interval

            if self.__tottime >= self.__maxtime:
                print 'Timing out...'
                self.end()
            
    def end(self):
        self.__flag=1
        
class MyTimer:

    def __init__(self):
        self.__interval = 5.0
        
    def __timerfunc(self):
        print 'Hello, this is the timer function!'

    def make_timer(self, interval):
        self.__interval = interval
        self.__timer = ModifiedTimer(self.__interval, 60.0, self.__timerfunc)
        self.__timer.start()

if __name__=="__main__":
    t=MyTimer()
    t.make_timer(10.0)
    
----------------------------------------------------------------

The code works as expected. I tested on Windows 98
using python 2.3.

-Anand Pillai




pythonguy at Hotpop.com (Anand Pillai) wrote in message news:<84fc4588.0310210106.6da894c1 at posting.google.com>...
> If you dont want to use sleep(), try this mechanism
> based on 'Timer' class in the threading module. 
> 
> 1. Create a timer thread that calls a function
>    which checks for the time stamp using os.stat().
> 2. Schedule the timer to wake up after 'n' seconds
>    and call this function.
> 3. If the call succeeds all and well, otherwise in
>    the function, create a new timer and set it again
>    to wake itself up after another 'n' seconds.
> 
> A timer can be used only once so you need to make a new timer
> for every wake-up call. Perhaps not very good on memory,
> but it might save you the CPU cycles.
> 
> You can wrap the whole thing in a class with the timer
> bound to a local class variable, and the function as
> another class attribute.
> 
> HTH.
> 
> -Anand
> 
> Tom <llafba_NOSPAM_ at gmx.net> wrote in message news:<bmpcos$2f0$1 at news.uni-kl.de>...
> > Lane LiaBraaten wrote:
> > 
> > >I would use os.stat() which returns all sorts of info about the file including 
> > >modification time.
> > >
> > >More info at: http://web.pydoc.org/1.5.2/os.html
> > >
> > >time=os.stat(file)[8]
> > >
> > ># analyze data
> > >
> > >while 1:
> > >	if os.stat(file)[8]>time:
> > >		#analyze data again
> > >  
> > >
> > Hi Lane,
> > 
> > thanks for your answer it works great and gives me a lot of new ideas 
> > that I can work with.
> > That "while 1" command looks interessting. I never used while that way. 
> > The Library Reference doesn't explain it. But am I right if I assume 
> > that this is  a loop that continues forever? Despite using break of 
> > course. I ask, because your suggestion works, but unfortunately uses 
> > 100% of my CPU power. :-( Well, it works, but is there maybe another way 
> > to do the same without using so much of my resources? :-) That would be 
> > great.
> > 
> > Thank's again.
> > Tom