On Sat, 25 Jul 2009 07:47:14 +0200, Andre Engels wrote: > On Sat, Jul 25, 2009 at 3:27 AM, Roy Smith<r...@panix.com> wrote: > >> Keep in mind that while a float may have a large apparent precision, >> there's no promise that the actual value returned by the OS has that >> much precision. You should be fine if all you're looking for is ms, >> but I wouldn't count on much more than that. > > Even stronger: I wouldn't count on _anything_ more than that. On my > machine, time.time() changes value once per millisecond. I tested this > by looking at a loop that recorded time.time() 100000 times. The total > time in the loop was 61 ms; out of the 100000 numbers, 61 were higher > than the previous one, with the highest difference being 1.00017 ms, the > lowest 0.999928 ms.
I'm guessing you're running Windows, because for Windows time.time() has a low resolution and time.clock() is the higher resolution timer. I'm running Linux, which is the opposite: >>> from time import time, clock >>> def diffs(alist): ... deltas = [] ... for i in xrange(1, len(alist)): ... deltas.append( alist[i] - alist[i-1] ) ... return deltas ... >>> d = [time() for i in xrange(10000)] # grab raw times >>> dt = diffs(d) # calculate the difference between each call >>> max(dt), min(dt) (0.00060892105102539062, 1.9073486328125e-06) >>> >>> d = [clock() for i in xrange(10000)] # and again using clock() >>> dc = diffs(d) >>> max(dc), min(dc) (0.010000000000000009, 0.0) More important than the maximum and minimum time deltas is the resolution of ticks in each timer. Under Linux, clock() hardly ever gets updated: >>> len(dc) # how many time deltas? 9999 >>> len(filter(None, dc)) # how many non-zero deltas? 2 while time() gets updated frequently: >>> len(dt) 9999 >>> len(filter(None, dt)) 9999 See also the comments in the timeit module. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
