On 19/03/2015 01:07, Alan Gauld wrote:
On 18/03/15 23:55, Steven D'Aprano wrote:
You don't say what your environment is but you should be aware
that Python is not really a suitable tool for real time
programming, especially if it safety critical.
I wouldn't want to use Python to control the critical parts of a nuclear
reactor or a plane's autopilot, but people use it to control mechanical
devices in near-real-time.
Yes, and that's the crux. Near real-time is fine, especially if
nobody will die.
comp.lang.python newsgroup who (I think) uses Python to drive some sort
of circuit board mechanical etching machine.
Using Python to control (say) an Arduino is pretty popular too.
Yes, I use Python on my Raspberry Pi and on an Arduino, it's fine for
that kind of thing. (Actually the Arduino can do real real-time stuff,
but the Pi can't.)
My concern was the OPs comment that:
" I must turn off that relay or harm may occur."
Now if the 'harm' is just a mucked up circuit board it's not such
a big deal.
But, if its a flooded field, a damaged machine costing $100Ks or even a
person's life then it's important to point out that python may not
be the tool of choice!
Similarly, if the time to turn it off is more than a second, say,
its not an issue. But if its less than a couple of milliseconds
then I'd be worried.
Maybe I spent too many years designing hard-real-time safety
critical systems. But a little bell always goes off in my head
when I read stuff like "...or harm may occur"
All depends on your definition of real time. Most systems we usually
mean pretty darn fast, but the control system for the rudder on a super
tanker is real time but takes minutes for the command to change course
to take effect.
--
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.
Mark Lawrence
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