It does work, but I was stunned at how long it took to switch the outlet on or off: a couple of seconds! I should disclaim that it's running on a rather underpowered machine (the OLPC XO-1 with a Geode x86 CPU @ 430MHz), but this was way too long to be acceptable:
$ time py-usbpower query Power: on real 0m2.690s user 0m1.484s sys 0m0.096sWith some detective work, I discovered that ctypes is doing things like running the compiler, objdump(!) and ldconfig(!), several times (!!), at each invocation of the program. (this is python2.5, but it looks like Python 2.7's ctypes still does essentially the same thing, unfortunately)
I set about to code this in C. For my reward, I got a very fast-executing program:
$ time c-usbpower status ON real 0m0.007s user 0m0.000s sys 0m0.000s
That's something like a 384x speedup. Lesson? ctypes has some very substantial startup costs for loading a library. It may be enough to make it unsuitable for a short-lived program.
In case it's useful to you, I enclose a copy of my usbpower program. It's under the terms of the GNU GPLv2.
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Entry first conceived on 28 February 2012, 3:19 UTC, last modified on 6 March 2012, 1:38 UTC
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