python - time.time vs. timeit.timeit

Question

Sometimes, I like to time how long it takes parts of my code to run. I've checked a lot of online sites and have seen, at large, two main ways to do this. One is using time.time and the other is using timeit.timeit.

So, I wrote a very simple script to compare the two:

from timeit import timeit
from time import time
start = time()
for i in range(100): print('ABC')
print(time()-start, timeit("for i in range(100): print('ABC')", number=1))

Basically, it times how long it takes to print "ABC" 100 times in a for-loop. The number on the left is the results for time.time and the number on the right is for timeit.timeit:

# First run
0.0 0.012654680972022981
# Second run
0.031000137329101562 0.012747430190149865
# Another run
0.0 0.011262325239660349
# Another run
0.016000032424926758 0.012740166697164025
# Another run
0.016000032424926758 0.0440628627381413

As you can see, sometimes, time.time is faster and sometimes it's slower. Which is the better way (more accurate)?

Answer 1

timeit is more accurate, for three reasons:

• it repeats the tests many times to eliminate the influence of other tasks on your machine, such as disk flushing and OS scheduling.
• it disables the garbage collector to prevent that process from skewing the results by scheduling a collection run at an inopportune moment.
• it picks the most accurate timer for your OS, time.time or time.clock in Python 2 and time.perf_counter() on Python 3. See timeit.default_timer.