[Tutor] using Python with time | MindStorms & Python

[rob@jam.rr.com]

Thanks! I did discover the time module right after posting my question,
and went ahead and had a little fun with time.sleep() before seeing your
responses. (The results of this foolishness are up on Useless Python
since I wound up writing a script that makes fun of script kiddie
viruses.

So far, about the only other programming experience I enjoy as much as
Python is my Lego MindStorms, which reminds me.... Has anyone had a
chance to try programming a MindStorms robot with Python? I've seen talk
of such on the web, but not had a chance to really investigate yet. I
definitely want to program my bots with Python!

Rob

Tim Peters wrote:
> 
> [rob@jam.rr.com]
> > I'd like to write a Python app that I can run "in the background" in
> > both Windows and Linux/BSD/*nix, although it's hardly mission-critical
> > that this be cross-platform.
> 
> The good news is that it will be cross-platform without even trying.
> 
> > What I'd like it to do is notify me at certain times of day (say,
> > at 10:32 a.m. and 3:40 p.m.) or after a given interval of time (say,
> > every XYZ minutes from the moment the app is activated).
> >
> > My practical aim for it is to have a way to remind myself to practice
> > mindfulness every so often during the day, but I'm also curious how to
> > handle the timing part of the code. If anyone could recommend where I
> > can look on the timing part, I'll credit helpful folk when I post the
> > code to Useless Python!</bribe>
> 
> Everything you need is in the time module, so read the docs for that.  I'm
> afraid the facilities in the time module are based closely on a horrible old
> Unix interface for dealing with time, so there's not a lot there that will
> make any sort of intuitive sense.  This is where an interactive shell is
> *essential*, so you can play with the time functions until what they really
> do "clicks" for you:
> 
> >>> import time
> >>> time.time()
> >>> print time.time()
> 988084770.06
> >>> # and about 6 seconds later
> >>> print time.time()
> 988084776.32
> >>>
> 
> So that's your first tool:  time.time() returns a number that goes up by one
> each second.  So if you want to wait, say, for 3 minutes "from now", here's
> one (but bad!) way to do that:
> 
>     now = time.time()
>     while time.time() < now + 3*60:
>         pass
> 
> That's a really bad way to do it because it will keep your CPU busy the
> entire time, running time.time() just as fast and often as it can.
> 
> The other tool you need is time.sleep():
> 
> >>> time.sleep(5)
> >>>
> 
> You have to *try* that to get anything useful out of the example <wink>:
> what happens is that, after hitting ENTER, the interactive shell just appears
> to freeze for 5 seconds before you get a prompt back.  Python's time.sleep(x)
> is a portable way to tell the operating system "I don't want to do *anything*
> for the next x seconds -- please just ignore me and do other stuff until x
> seconds have elapsed, then please remember to wake me up again".  This lets
> you wait a long time without interfering with other programs.
> 
> So if you've got N seconds remaining to wait, time.sleep(N) will put your
> program to sleep for *about* N seconds.  It's better to sleep a little less
> than that, because the OS may not wake you up *exactly* when N seconds have
> elapsed, and the longer your program has been sleeping, the more likely that
> the OS has swapped it out of main memory and onto disk.  Then, depending on
> your system, it make take the OS a couple seconds just to read your program
> back into memory again so it can continue running it!
> 
> That's all nasty details, though.  To a reasonably good first approximation,
> if you want your program to wait for an hour, the one-liner
> 
>     time.sleep(60*60)
> 
> will get pretty close.  So start with that, then play around with the
> combination of that and a "busy loop" (the "really bad" method above -- which
> isn't bad at all when waiting for very *short* periods of time) to imporve
> the accuracy.
> 
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