CODEWITHSUNDEEP
pythonpython-3.xtime
Patrik Pyrzanowski
Patrik Pyrzanowski

Reputation: 25

Python most accurate method to measure time (ms)

I need to meassure the time certain parts of my code take. While executing my code on a powerfull server, I get 10 diffrent results

I tried comparing time measured with time.time(), time.perf_counter(), time.perf_counter_ns(), time.process_time() and time.process_time_ns().

import time

for _ in range(10):
    start = time.perf_counter()
    i = 0
    while i < 100000:
        i = i + 1
    time.sleep(1)
    end = time.perf_counter()
    print(end - start)

I'm expecting when executing the same code 10 times, to be the same (the results to have a resolution of at least 1ms) ex. 1.041XX and not 1.030sec - 1.046sec.

When executing my code on a 16 cpu, 32gb memory server I'm receiving this result:

1.045549364
1.030857833
1.0466020120000001
1.0309665050000003
1.0464690349999994
1.046397238
1.0309525370000001
1.0312070380000007
1.0307592159999999
1.046095523

Im expacting the result to be: 

1.041549364
1.041857833
1.0416020120000001
1.0419665050000003
1.0414690349999994
1.041397238
1.0419525370000001
1.0412070380000007
1.0417592159999999
1.041095523

Upvotes: 2

Views: 615

Answers (2)

ludovjb
ludovjb

Reputation: 66

Perfoming a code do not take the same time at each loop iteration because of the scheduling of the system (system puts on hold your process to perform another process then back to it...).

Upvotes: 2

Patrick Artner
Patrick Artner

Reputation: 51623

Your expectations are wrong. If you want to measure code average time consumption use the timeit module. It executes your code multiple times and averages over the times.

The reason your code has different runtimes lies in your code:

time.sleep(1)  # ensures (3.5+) _at least_ 1000ms are waited, won't be less, might be more

You are calling it in a tight loop,resulting in accumulated differences:

Quote from time.sleep(..) documentation:

Suspend execution of the calling thread for the given number of seconds. The argument may be a floating point number to indicate a more precise sleep time. The actual suspension time may be less than that requested because any caught signal will terminate the sleep() following execution of that signal’s catching routine. Also, the suspension time may be longer than requested by an arbitrary amount because of the scheduling of other activity in the system.

Changed in version 3.5: The function now sleeps at least secs even if the sleep is interrupted by a signal, except if the signal handler raises an exception (see PEP 475 for the rationale).

Emphasis mine.

Upvotes: 3

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