Question

Is there a way to test, using Python, how long the system has been idle on Mac? Or, failing that, even if the system is currently idle?

Answer

Using the information from the accepted solution, here is an ugly but functional and fairly efficient function for the job:

from subprocess import *

def idleTime():
    '''Return idle time in seconds'''

    # Get the output from 
    # ioreg -c IOHIDSystem
    s = Popen(["ioreg", "-c", "IOHIDSystem"], stdout=PIPE).communicate()[0]
    lines = s.split('\n')

    raw_line = ''
    for line in lines:
        if line.find('HIDIdleTime') > 0:
            raw_line = line
            break

    nano_seconds = long(raw_line.split('=')[-1])
    seconds = nano_seconds/10**9
    return seconds

Answer 1

Untested (for now), but according to this thread you could parse the output of

ioreg -c IOHIDSystem