How to terminate the function that runs every n seconds

Mark Lawrence breamoreboy at
Wed Jan 14 18:54:00 CET 2015

On 14/01/2015 17:37, Grant Edwards wrote:
> On 2015-01-14, Mark Lawrence <breamoreboy at> wrote:
>> On 14/01/2015 16:33, Dave Angel wrote:
>>> Note that neither Timer nor sleep makes any promises about how
>>> accurately it matches the requested time.
>> Reminds me of working on Telematics S200/300/4000/5000 telecomms kit in
>> the early 90s where the timers were mains based, so a one hour timer
>> would go off at about one hour, 30 seconds.
> I don't understand.  Power line frequencies are _very_ accurate and
> have been relied upon for timekeeping since the 1930s.  We're talking
> a few hundred PPM over a 24 hour period.  A 30 second error over a one
> hour period seems _really_ high.

"National Grid has a licence obligation to control frequency within the 
limits specified in the 'Electricity Supply Regulations', i.e. ±1% of 
nominal system frequency (50.00Hz) save in abnormal or exceptional 
circumstances.".  I wouldn't describe ±1% as very accurate and certainly 
not within a few hundred ppm.  I'm assuming that this kind of limitation 
applies around the world, so could you be getting confused with some 
other more accurate frequency control?

My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

More information about the Python-list mailing list