calculating system clock resolution

[Steven D'Aprano]

On Sat, 08 Apr 2006 04:16:20 -0700, jUrner wrote:

> def calc_time_res():
>     now = time.time
>     start = now()
>     x = start
>     while start == x:
>         x = now()
>     print x, start  # <--
>     print x - start
> 
> print calc_time_res()
>>> 1.50203704834e-05
> 
> Something is going wrong here.
> If you look at the function ,time.time() returns time in microseconds
> (most oses and so does mine).

>From help(time.time):

    time() -> floating point number
    Return the current time in seconds since the Epoch.
    Fractions of a second may be present if the system clock provides them.

Seconds, not microseconds.


> So the calculation goes, lets say 1.23 - 1.24

How can the time *after* the while loop be less than the time *before* the
while loop?

> How can the result be something like 1.50203704834e-05 ?

Have you looked at the output of time.time()?

>>> time.time()
1144496209.3221531

Of course, Python only prints a certain number of digits; to see the full
amount, use string formatting:

>>> '%40.30f' % time.time()
'1144496642.905987024307250976562500000000'


This brings me to an even simpler method of getting the resolution of
time.time(), without the overhead of a while loop:

>>> abs(time.time() - time.time())
1.0013580322265625e-05

which is approximately 0.01ms, just as you expected.



-- 
Steven.