Question

When I run the code below outside of timeit(), it appears to complete instantaneously. However when I run it within the timeit() function, it takes much longer. Why?

>>> import timeit
>>> t = timeit.Timer("3**4**5")
>>> t.timeit()
16.55522028637718

Using:
Python 3.1 (x86) –
AMD Athlon 64 X2 –
WinXP (32 bit)

Answer 1

The timeit() function runs the code many times (default one million) and takes an average of the timings.

To run the code only once, do this:

t.timeit(1)

but that will give you skewed results – it repeats for good reason.

To get the per-loop time having let it repeat, divide the result by the number of loops. Use a smaller value for the number of repeats if one million is too many:

count = 1000
print t.timeit(count) / count