Test Python's random number generation time in edge cases for StackOverflow

random-speed-test.py

#!/user/bin/env python3

# Code written while writing this StackOverflow answer:
# https://stackoverflow.com/a/58126026

from timeit import timeit

def test(bit_lengths, trials=10000, unit=1000, rounding=16):
    """Test how long it takes to find a random n-bit number less than the largest
    and smallest number with exactly that many bits.

    See https://stackoverflow.com/a/58126026 for details.

    bit_lengths = iterable of bit-lengths to test
    trials = number of runs for the highest and lowest number of each bit length
    unit = times will be shown in (1/unit) seconds (e.g. 1000 for milliseconds)
    rounding = how many digits to show
    """
    scale = unit
    r = rounding
    col1 = max(len('bits'), len(str(max(bit_lengths)))) # length of 1st header
    sep = '   '

    h1 = f'{"2 ** (n - 1)":<{r+2}}'
    if len(h1) > r + 2:
        h1 = f'{"low":<{r+2}}'

    h2 = f'{"(2 ** n) - 1":<{r+2}}'
    if len(h2) > r + 2:
        h2 = f'{"high":<{r+2}}'

    print(f'{"bits":>{col1}}', h1, h2, 'ratio', sep=sep)

    for n in bit_lengths:
        low = 2 ** (n - 1)
        high = 2 ** n - 1
        lowtime = timeit(f'randrange({low})',
                         setup='from random import randrange',
                         number=trials) * scale / trials
        hightime = timeit(f'randrange({high})',
                          setup='from random import randrange',
                          number=trials) * scale / trials

        low = f'{lowtime:.{r}f}'.rstrip('0')
        high = f'{hightime:.{r}f}'.rstrip('0')
        ratio = f'{lowtime / hightime :.{r}f}'.rstrip('0')
        print(f'{n:>{col1}}',
              f'{low: <{r+2}}',
              f'{high: <{r+2}}',
              f'{ratio:<{r+2}}', sep=sep)

if __name__ == '__main__':
    test([2 ** n for n in range(6, 12)],
         trials=1_000_000,
         unit=1_000_000, # microseconds
         rounding=10)