pythontimeitdebian-stretch

Why does timeit report slower code as faster one?

I tested this with python 3.5 in Debian Stretch.
I tried benchmark the "Avoiding dots" optimization.
As expected, the "Avoiding dots" optimization is really much faster.
Unexpected, timeit reports the slower code as the faster. What is the reason?

$ time python3 -m timeit -s "s=''" "s.isalpha()"
10000000 loops, best of 3: 0.119 usec per loop

real    0m5.023s
user    0m4.922s
sys 0m0.012s
$ time python3 -m timeit -s "isalpha=str.isalpha;s=''" "isalpha(s)"
1000000 loops, best of 3: 0.212 usec per loop

real    0m0.937s
user    0m0.927s
sys 0m0.000s
Solution

  • timeit did 10 times as many iterations in the “slow” case. It adaptively tries more iterations to find a number that balances statistical quality and waiting time.