Continuously running scripts question

[Ian Kelly]

On Fri, Jun 25, 2010 at 9:49 AM,  <jyoung79 at kc.rr.com> wrote:
> Currently, I have some scripts (in particular, applescript
> 'stay-open' scripts) that run continuously on a Mac through
> the day.  They look in a certain folder every 30 seconds and
> perform the necessary work needed.
>
> I was curious if anyone here on the list does anything similar
> with Python?  If so, do you use launchd, cron, etc in order to
> start up your Python script at the appropriate time(s)?  Or do
> you just let your Python code run continuously?  I'm curious of
> the pros and cons with each of these.  I'm assuming launchd (or
> something similar) is probably the better option since if a
> script broke it would start it back up again the next time
> around.  Launchd also probably doesn't use as much processing
> power?

I use cron.

Pro:  You don't have to worry about an unusual exception crashing your
script and requiring a restart.  You fix the exception when you can,
and in the meantime your script is still being run.

Con:  Most cron implementations have a maximum frequency of once per minute.
Con:  Starting a fresh Python interpreter is expensive, and doing it
once or twice per minute could add significantly if the system is
already under a heavy load.

When I do this, my scripts generally run once every 15 minutes or
thereabouts, so the cons don't really apply.

Cheers,
Ian